1.
Mid-ocean ridge
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A mid-ocean ridge is an underwater mountain system formed by plate tectonics. It consists of various mountains linked in chains, typically having a known as a rift running along its spine. This type of mountain ridge is characteristic of what is known as an oceanic spreading center. The production of new results from mantle upwelling in response to plate spreading. The buoyant melt rises as magma at a linear weakness in the oceanic crust, a mid-ocean ridge demarcates the boundary between two tectonic plates, and consequently is termed a divergent plate boundary. Mid-ocean ridges are geologically active, with new magma constantly emerging onto the floor and into the crust at. The crystallized magma forms new crust of basalt and gabbro and they are formed by two oceanic plates moving away from each other. The rocks making up the crust below the seafloor are youngest along the axis of the ridge and age with increasing distance from that axis, new magma of basalt composition emerges at and near the axis because of decompression melting in the underlying Earths mantle. The oceanic crust is made up of much younger than the Earth itself. Most oceanic crust in the basins is less than 200 million years old. The crust is in a constant state of renewal at the ocean ridges, moving away from the mid-ocean ridge, ocean depth progressively increases, the greatest depths are in ocean trenches. As the oceanic crust moves away from the axis, the peridotite in the underlying mantle cools. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere, by contrast, fast spreading ridges like the East Pacific Rise are narrow, sharp incisions surrounded by generally flat topography that slopes away from the ridge over many hundreds of miles. The overall shape of ridges results from Pratt isostacy, close to the ridge there is hot. As the oceanic plates cool, away from the axes, the oceanic mantle lithosphere thickens. Thus older seafloor is underlain by denser material and sits lower, there are two processes, ridge-push and slab pull, thought to be responsible for the spreading seen at mid-ocean ridges, and there is some uncertainty as to which is dominant. Ridge-push occurs when the bulk of the ridge pushes the rest of the tectonic plate away from the ridge. At the subduction zone, slab-pull comes into effect and this is simply the weight of the tectonic plate being subducted below the overlying plate dragging the rest of the plate along behind it
2.
Oceanic crust
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Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. The crust overlies the solidified and uppermost layer of the mantle, the crust and the solid mantle layer together constitute oceanic lithosphere. Oceanic crust is the result of erupted mantle material originating from below the plate, cooled and in most instances and this occurs mostly at mid-ocean ridges, but also at scattered hotspots, and also in rare but powerful occurrences known as flood basalt eruptions. It is primarily composed of rocks, or sima, which is rich in iron. Although a complete section of oceanic crust has not yet been drilled, Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. Layer 1 is on an average 0.4 km thick and it consists of unconsolidated or semiconsolidated sediments, usually thin or even not present near the mid-ocean ridges but thickens farther away from the ridge. Layer 3 is formed by slow cooling of magma beneath the surface and consists of coarse grained gabbros and it constitutes over two-thirds of oceanic crust volume with almost 5 km thickness. The most voluminous volcanic rocks of the floor are the mid-oceanic ridge basalts. These rocks have low concentrations of large ion lithophile elements, light rare earth elements, volatile elements, there can be found basalts enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands, the Azores and Iceland. Oceanic crust is continuously being created at mid-ocean ridges, as plates diverge at these ridges, magma rises into the upper mantle and crust. As it moves away from the ridge, the lithosphere becomes cooler and denser, the youngest oceanic lithosphere is at the oceanic ridges, and it gets progressively older away from the ridges. As the mantle rises it cools and melts, as the pressure decreases, the amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness, an example of this is the Gakkel Ridge under the Arctic Ocean. Thicker than average crust is found above plumes as the mantle is hotter and hence it crosses the solidus and melts at a depth, creating more melt. An example of this is Iceland which has crust of thickness ~20 km, the oceanic lithosphere subducts at what are known as convergent boundaries. These boundaries can exist between oceanic lithosphere on one plate and oceanic lithosphere on another, or between oceanic lithosphere on one plate and continental lithosphere on another, in the second situation, the oceanic lithosphere always subducts because the continental lithosphere is less dense. The subduction process consumes older oceanic lithosphere, so oceanic crust is more than 200 million years old. The process of super-continent formation and destruction via repeated cycles of creation and destruction of oceanic crust is known as the Wilson cycle, the oldest large scale oceanic crust is in the west Pacific and north-west Atlantic - both are about up to 180-200 million years old
3.
Volcano
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A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Earths volcanoes occur because its crust is broken into 17 major, therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. This type of volcanism falls under the umbrella of plate hypothesis volcanism, Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called hotspots, for example Hawaii, are postulated to arise from upwelling diapirs with magma from the boundary,3,000 km deep in the Earth. Volcanoes are usually not created where two plates slide past one another. Erupting volcanoes can pose hazards, not only in the immediate vicinity of the eruption. Historically, so-called volcanic winters have caused catastrophic famines, the word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology. The study of volcanoes is called volcanology, sometimes spelled vulcanology, at the mid-oceanic ridges, two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock. Most divergent plate boundaries are at the bottom of the oceans, therefore, most volcanic activity is submarine, black smokers are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the temperature of the overlying mantle wedge. This magma tends to be very viscous due to its high content, so it often does not reach the surface. When it does reach the surface, a volcano is formed, typical examples of this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire. Because tectonic plates move across them, each volcano becomes dormant and is eventually re-formed as the plate advances over the postulated plume and this theory is currently under criticism, however. The most common perception of a volcano is of a mountain, spewing lava and poisonous gases from a crater at its summit, however. The features of volcanoes are more complicated and their structure. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have features such as massive plateaus
4.
Alfred Wegener
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Alfred Lothar Wegener was a German polar researcher, geophysicist and meteorologist. Wegener was involved in expeditions to Greenland to study polar air circulation before the existence of the jet stream was accepted. Alfred Wegener was born in Berlin on 1 November 1880 as the youngest of five children in a clergymans family and his father, Richard Wegener, was a theologian and teacher of classical languages at the Berlinisches Gymnasium zum Grauen Kloster. In 1886 his family purchased a manor house near Rheinsberg. Today there is an Alfred Wegener Memorial site and tourist information office in a building that was once the local schoolhouse. He was cousin to movie pioneer Paul Wegener, Wegener attended school at the Köllnisches Gymnasium on Wallstrasse in Berlin, graduating as the best in his class. Afterward he studied Physics, meteorology and Astronomy in Berlin, Heidelberg, from 1902 to 1903 during his studies he was an assistant at the Urania astronomical observatory. He obtained a doctorate in astronomy in 1905 based on a dissertation written under the supervision of Julius Bauschinger at Friedrich Wilhelms University, Wegener had always maintained a strong interest in the developing fields of meteorology and climatology and his studies afterwards focused on these disciplines. In 1905 Wegener became an assistant at the Aeronautisches Observatorium Lindenberg near Beeskow and he worked there with his brother Kurt, two years his senior, who was likewise a scientist with an interest in meteorology and polar research. The two pioneered the use of balloons to track air masses.5 hours from April 5–7,1906. In that same year 1906, Wegener participated in the first of his four Greenland expeditions, the expedition was led by the Dane Ludvig Mylius-Erichsen and charged with studying the last unknown portion of the northeastern coast of Greenland. Here Wegener also made his first acquaintance with death in a wilderness of ice when the expedition leader, after his return in 1908 and until World War I, Wegener was a lecturer in meteorology, applied astronomy and cosmic physics at the University of Marburg. His students and colleagues in Marburg particularly valued his ability to clearly and understandably explain even complex topics, after a stopover in Iceland to purchase and test ponies as pack animals, the expedition arrived in Danmarkshavn. Even before the trip to the ice began the expedition was almost annihilated by a calving glacier. The Danish expedition leader, Johan Peter Koch, broke his leg when he fell into a glacier crevasse, Wegener and Koch were the first to winter on the inland ice in northeast Greenland. Inside their hut they drilled to a depth of 25 m with an auger, in summer 1913 the team crossed the inland ice, the four expedition participants covering a distance twice as long as Fridtjof Nansens southern Greenland crossing in 1888. Only a few kilometers from the western Greenland settlement of Kangersuatsiaq the small team ran out of food while struggling to find their way through difficult glacial breakup terrain. But at the last moment, after the last pony and dog had eaten, they were picked up at a fjord by the clergyman of Upernavik
5.
Continent
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A continent is one of several very large landmasses on Earth. Generally identified by convention rather than any strict criteria, up to seven regions are regarded as continents. Ordered from largest in size to smallest, they are, Asia, Africa, North America, South America, Antarctica, Europe, in geology, areas of continental crust include regions covered with water. Islands are frequently grouped with a continent to divide all the worlds land into geopolitical regions. Under this scheme, most of the countries and territories in the Pacific Ocean are grouped together with the continent of Australia to form a geopolitical region called Oceania. By convention, continents are understood to be large, continuous, discrete masses of land, many of the seven most commonly recognized continents identified by convention are not discrete landmasses separated completely by water. Earths major landmasses all have coasts on a single, continuous World Ocean, the most restricted meaning of continent is that of a continuous area of land or mainland, with the coastline and any land boundaries forming the edge of the continent. From this perspective the edge of the shelf is the true edge of the continent. In this sense the islands of Great Britain and Ireland are part of Europe, while Australia, as a cultural construct, the concept of a continent may go beyond the continental shelf to include oceanic islands and continental fragments. In this way, Iceland is considered part of Europe and Madagascar part of Africa, extrapolating the concept to its extreme, some geographers group the Australasian continental plate with other islands in the Pacific into one continent called Oceania. This divides the land surface of Earth into continents or quasi-continents. The ideal criterion that each continent be a discrete landmass is commonly relaxed due to historical conventions, of the seven most globally recognized continents, only Antarctica and Australia are completely separated from other continents by ocean. Several continents are defined not as absolutely distinct bodies but as more or less discrete masses of land, Asia and Africa are joined by the Isthmus of Suez, and North and South America by the Isthmus of Panama. In both cases, there is no separation of these landmasses by water. Both these isthmuses are very narrow compared to the bulk off the landmasses they unite, North America and South America are treated as separate continents in the seven-continent model. However, they may also be viewed as a continent known as America or the Americas. This viewpoint was common in the United States until World War II and this remains the more common vision in Latin American countries, Spain, Portugal, France, Italy and Greece, where they are taught as a single continent. The criterion of a landmass is completely disregarded if the continuous landmass of Eurasia is classified as two separate continents, Europe and Asia
6.
Princeton University
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Princeton University is a private Ivy League research university in Princeton, New Jersey, United States. The institution moved to Newark in 1747, then to the current site nine years later, Princeton provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences, and engineering. The university has ties with the Institute for Advanced Study, Princeton Theological Seminary, Princeton has the largest endowment per student in the United States. The university has graduated many notable alumni, two U. S. Presidents,12 U. S. Supreme Court Justices, and numerous living billionaires and foreign heads of state are all counted among Princetons alumni body. New Light Presbyterians founded the College of New Jersey in 1746 in order to train ministers, the college was the educational and religious capital of Scots-Irish America. In 1754, trustees of the College of New Jersey suggested that, in recognition of Governors interest, gov. Jonathan Belcher replied, What a name that would be. In 1756, the moved to Princeton, New Jersey. Its home in Princeton was Nassau Hall, named for the royal House of Orange-Nassau of William III of England, following the untimely deaths of Princetons first five presidents, John Witherspoon became president in 1768 and remained in that office until his death in 1794. During his presidency, Witherspoon shifted the focus from training ministers to preparing a new generation for leadership in the new American nation. To this end, he tightened academic standards and solicited investment in the college, in 1812, the eighth president the College of New Jersey, Ashbel Green, helped establish the Princeton Theological Seminary next door. The plan to extend the theological curriculum met with approval on the part of the authorities at the College of New Jersey. Today, Princeton University and Princeton Theological Seminary maintain separate institutions with ties that include such as cross-registration. Before the construction of Stanhope Hall in 1803, Nassau Hall was the sole building. The cornerstone of the building was laid on September 17,1754, during the summer of 1783, the Continental Congress met in Nassau Hall, making Princeton the countrys capital for four months. The class of 1879 donated twin lion sculptures that flanked the entrance until 1911, Nassau Halls bell rang after the halls construction, however, the fire of 1802 melted it. The bell was then recast and melted again in the fire of 1855, James McCosh took office as the colleges president in 1868 and lifted the institution out of a low period that had been brought about by the American Civil War. McCosh Hall is named in his honor, in 1879, the first thesis for a Doctor of Philosophy Ph. D. was submitted by James F. Williamson, Class of 1877. In 1896, the officially changed its name from the College of New Jersey to Princeton University to honor the town in which it resides
7.
Convection
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Convection is the movement of groups of molecules within fluids such as liquids or gases, and within rheids. Convection takes place through advection, diffusion or both, convection cannot take place in solids because neither bulk current flows nor significant diffusion can take place in solids. Diffusion of heat can take place in solids, but that is called heat conduction, convective heat transfer is one of the major types of heat transfer, and convection is also a major mode of mass transfer in fluids. In the context of heat and mass transfer, the convection is used to refer to the sum of advective and diffusive transfer. In common use the term convection may refer loosely to heat transfer by convection, as opposed to mass transfer by convection, sometimes convection is even used to refer specifically to free heat convection as opposed to forced heat convection. However, in mechanics the correct use of the word is the general sense, convection can be qualified in terms of being natural, forced, gravitational, granular, or thermomagnetic. It may also be said to be due to combustion, capillary action, or Marangoni, heat transfer by natural convection plays a role in the structure of Earths atmosphere, its oceans, and its mantle. Discrete convective cells in the atmosphere can be seen as clouds, natural convection also plays a role in stellar physics. The word convection may have different but related usages in different scientific or engineering contexts or applications. The broader sense is in fluid mechanics, where convection refers to the motion of fluid regardless of cause, however, in thermodynamics convection often refers specifically to heat transfer by convection. Additionally, convection includes fluid movement both by bulk motion and by the motion of individual particles, however, in some cases, convection is taken to mean only advective phenomena. Convection occurs on a scale in atmospheres, oceans, planetary mantles. Fluid movement during convection may be slow, or it may be obvious and rapid. On astronomical scales, convection of gas and dust is thought to occur in the disks of black holes. Convective heat transfer is a mechanism of heat transfer occurring because of bulk motion of fluids, heat is the entity of interest being advected, and diffused. Heat is transferred by convection in numerous examples of naturally occurring fluid flow, such as, wind, oceanic currents, convection is also used in engineering practices of homes, industrial processes, cooling of equipment, etc. The rate of heat transfer may be improved by the use of a heat sink. For instance, a typical computer CPU will have a fan to ensure its operating temperature is kept within tolerable limits
8.
Asthenosphere
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The asthenosphere is the highly viscous, mechanically weak and ductilely deforming region of the upper mantle of the Earth. It lies below the lithosphere, at depths between approximately 80 and 200 km below the surface, the Lithosphere-Asthenosphere boundary is usually referred to as LAB. The asthenosphere is generally solid, although some of its regions could be melted, the lower boundary of the asthenosphere is not well defined. The thickness of the asthenosphere depends mainly on the temperature, in some regions the asthenosphere could extend as deep as 700 km. It is considered the region of mid-ocean ridge basalt. The asthenosphere is a part of the mantle just below the lithosphere that is involved in plate tectonic movement. The lithosphere-asthenosphere boundary is taken at the 1300 °C isotherm, above which the mantle behaves in a rigid fashion. Seismic waves pass relatively slowly through the asthenosphere compared to the lithospheric mantle, thus it has been called the low-velocity zone. This decreasing in seismic waves velocity from lithosphere to asthenosphere could be caused by the presence of a small percentage of melt in the asthenosphere. The lower boundary of the LVZ lies at a depth of 180–220 km, in the old oceanic mantle the transition from the lithosphere to the asthenosphere, the so-called lithosphere-asthenosphere boundary is shallow with a sharp and large velocity drop. At the mid-ocean ridges the LAB rises to within a few kilometers of the ocean floor, the upper part of the asthenosphere is believed to be the zone upon which the great rigid and brittle lithospheric plates of the Earths crust move about. In this way, it flows like a current, radiating heat outward from the Earths interior. Above the asthenosphere, at the rate of deformation, rock behaves elastically and, being brittle, can break. The rigid lithosphere is thought to float or move about on the slowly flowing asthenosphere, an Introduction to the Solar System. San Diego State University, The Earths internal heat energy and interior structure
9.
Plasticity (physics)
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In physics and materials science, plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces. For example, a piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself. In engineering, the transition from elastic behavior to plastic behavior is called yield, plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, foams, bone and skin. However, the mechanisms that cause plastic deformation can vary widely. At a crystalline scale, plasticity in metals is usually a consequence of dislocations, such defects are relatively rare in most crystalline materials, but are numerous in some and part of their crystal structure, in such cases, plastic crystallinity can result. In brittle materials such as rock, concrete and bone, plasticity is caused predominantly by slip at microcracks, for many ductile metals, tensile loading applied to a sample will cause it to behave in an elastic manner. Each increment of load is accompanied by an increment in extension. When the load is removed, the returns to its original size. However, once the load exceeds a threshold – the yield strength – the extension increases more rapidly than in the region, now when the load is removed. Elastic deformation, however, is an approximation and its quality depends on the time frame considered, if, as indicated in the graph opposite, the deformation includes elastic deformation, it is also often referred to as elasto-plastic deformation or elastic-plastic deformation. Perfect plasticity is a property of materials to undergo irreversible deformation without any increase in stresses or loads, plastic materials with hardening necessitate increasingly higher stresses to result in further plastic deformation. Generally, plastic deformation is dependent on the deformation speed. Such materials are said to deform visco-plastically, the plasticity of a material is directly proportional to the ductility and malleability of the material. Plasticity in a crystal of pure metal is primarily caused by two modes of deformation in the lattice, slip and twinning. Slip is a deformation which moves the atoms through many interatomic distances relative to their initial positions. Twinning is the plastic deformation takes place along two planes due to a set of forces applied to a given metal piece. Most metals show more plasticity when hot than when cold, lead shows sufficient plasticity at room temperature, while cast iron does not possess sufficient plasticity for any forging operation even when hot. This property is of importance in forming, shaping and extruding operations on metals, most metals are rendered plastic by heating and hence shaped hot
10.
Continental drift
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Continental drift is the movement of the Earths continents relative to each other, thus appearing to drift across the ocean bed. The speculation that continents might have drifted was first put forward by Abraham Ortelius in 1596, the concept was independently and more fully developed by Alfred Wegener in 1912, but his theory was rejected by some for lack of a mechanism and others because of prior theoretical commitments. The idea of continental drift has been subsumed by the theory of plate tectonics, W. J. Kious described Ortelius thoughts in this way, Abraham Ortelius in his work Thesaurus Geographicus. Suggested that the Americas were torn away from Europe and Africa, by earthquakes and floods and went on to say, The vestiges of the rupture reveal themselves, if someone brings forward a map of the world and considers carefully the coasts of the three. In his Manual of Geology,1863, Dana says The continents, Dana was enormously influential in America – his Manual of Mineralogy is still in print in revised form – and the theory became known as Permanence theory. This suggested that the oceans were a permanent feature of the earths surface and this led Mantovani to propose an Expanding Earth theory which has since been shown to be incorrect. Continental drift without expansion was proposed by Frank Bursley Taylor, who suggested in 1908 that the continents were moved into their present positions by a process of continental creep. Wegener said that of all theories, Taylors, although not fully developed, had the most similarities to his own. In the mid-20th century, the theory of drift was referred to as the Taylor-Wegener hypothesis. Alfred Wegener first presented his hypothesis to the German Geological Society on January 6,1912 and his hypothesis was that the continents had once formed a single landmass, called Pangea, before breaking apart and drifting to their present locations. Wegener was the first to use the continental drift and formally publish the hypothesis that the continents had somehow drifted apart. Although he presented evidence for continental drift, he was unable to provide a convincing explanation for the physical processes which might have caused this drift. The Polflucht hypothesis was studied by Paul Sophus Epstein in 1920. The theory of drift was not accepted for many years. One problem was that a driving force was missing. A second problem was that Wegeners estimate of the velocity of continental motion,250 cm/year, was implausibly high, and it did not help that Wegener was not a geologist. Other geologists also believed that the evidence that Wegener had provided was not sufficient, the British geologist Arthur Holmes championed the theory of continental drift at a time when it was deeply unfashionable. He proposed in 1931 that the Earths mantle contained convection cells that dissipated radioactive heat and his Principles of Physical Geology, ending with a chapter on continental drift, was published in 1944
11.
Plate tectonics
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The theoretical model builds on the concept of continental drift developed during the first few decades of the 20th century. The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s, the lithosphere, which is the rigid outermost shell of a planet, is broken up into tectonic plates. The Earths lithosphere is composed of seven or eight major plates, where the plates meet, their relative motion determines the type of boundary, convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries. The relative movement of the plates typically ranges from zero to 100 mm annually, tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction carries plates into the mantle, the material lost is balanced by the formation of new crust along divergent margins by seafloor spreading. In this way, the surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle, earlier theories, since disproven, proposed gradual shrinking or gradual expansion of the globe. Tectonic plates are able to move because the Earths lithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from the ridge and drag, with downward suction. Another explanation lies in the different forces generated by forces of the Sun. The relative importance of each of these factors and their relationship to other is unclear. The outer layers of the Earth are divided into the lithosphere and asthenosphere and this is based on differences in mechanical properties and in the method for the transfer of heat. Mechanically, the lithosphere is cooler and more rigid, while the asthenosphere is hotter, in terms of heat transfer, the lithosphere loses heat by conduction, whereas the asthenosphere also transfers heat by convection and has a nearly adiabatic temperature gradient. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, Plate motions range up to a typical 10–40 mm/year, to about 160 mm/year. The driving mechanism behind this movement is described below, tectonic lithosphere plates consist of lithospheric mantle overlain by either or both of two types of crustal material, oceanic crust and continental crust. Average oceanic lithosphere is typically 100 km thick, its thickness is a function of its age, as passes, it conductively cools
12.
Divergent boundary
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In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which eventually become rift valleys, most active divergent plate boundaries occur between oceanic plates and exist as mid-oceanic ridges. Divergent boundaries also form volcanic islands which occur when the plates apart to produce gaps which molten lava rises to fill. Current research indicates that complex convection within the Earths mantle allows material to rise to the base of the lithosphere beneath each divergent plate boundary. This supplies the area with vast amounts of heat and a reduction in pressure that melts rock from the asthenosphere beneath the area forming large flood basalt or lava flows. Each eruption occurs in only a part of the boundary at any one time. Over millions of years, tectonic plates may move many hundreds of kilometers away from both sides of a divergent plate boundary, because of this, rocks closest to a boundary are younger than rocks further away on the same plate. At divergent boundaries, two plates move apart from other and the space that this creates is filled with new crustal material sourced from molten magma that forms below. The origin of new divergent boundaries at triple junctions is thought to be associated with the phenomenon known as hotspots. Here, exceedingly large convective cells bring very large quantities of hot asthenospheric material near the surface, the hot spot which may have initiated the Mid-Atlantic Ridge system currently underlies Iceland which is widening at a rate of a few centimeters per year. Divergent boundaries can create massive fault zones in the ridge system. Spreading is generally not uniform, so where spreading rates of adjacent ridge blocks are different and these are the fracture zones, many bearing names, that are a major source of submarine earthquakes. A sea floor map will show a strange pattern of blocky structures that are separated by linear features perpendicular to the ridge axis. If one views the sea floor between the zones as conveyor belts carrying the ridge on each side of the rift away from the spreading center the action becomes clear. Crest depths of the old ridges, parallel to the current spreading center and it is at mid-ocean ridges that one of the key pieces of evidence forcing acceptance of the seafloor spreading hypothesis was found. Airborne geomagnetic surveys showed a pattern of symmetrical magnetic reversals on opposite sides of ridge centers. The pattern was far too regular to be coincidental as the widths of the bands were too closely matched. Scientists had been studying polar reversals and the link was made by Lawrence W. Morley, Frederick John Vine, the magnetic banding directly corresponds with the Earths polar reversals
13.
Lithosphere
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A lithosphere is the rigid, outermost shell of a terrestrial-type planet or natural satellite that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a planet, the crust, is defined on the basis of its chemistry. Earths lithosphere includes the crust and the uppermost mantle, which constitute the hard, the lithosphere is subdivided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the forming process is called the pedosphere. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, the study of past and current formations of landscapes is called geomorphology. The concept of the lithosphere as Earth’s strong outer layer was described by A. E. H, love in his 1911 monograph Some problems of Geodynamics and further developed by Joseph Barrell, who wrote a series of papers about the concept and introduced the term lithosphere. The concept was based on the presence of significant gravity anomalies over continental crust and these ideas were expanded by Reginald Aldworth Daly in 1940 with his seminal work Strength and Structure of the Earth and have been broadly accepted by geologists and geophysicists. The temperature at which olivine begins to deform viscously is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle, the mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the mantle by the change in chemical composition that takes place at the Moho discontinuity. Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle and is denser than continental lithosphere, oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick, the thickness of the mantle part of the oceanic lithosphere can be approximated as a thermal boundary layer that thickens as the square root of time. H ∼2 κ t Here, h is the thickness of the mantle lithosphere, κ is the thermal diffusivity for silicate rocks. The age is equal to L/V, where L is the distance from the spreading centre of mid-oceanic ridge. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years and this is because the chemically differentiated oceanic crust is lighter than asthenosphere, but thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones, geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths brought up in kimberlite, lamproite, and other volcanic pipes. The histories of these xenoliths have been investigated by many methods, such studies have confirmed that mantle lithospheres below some cratons have persisted for periods in excess of 3 billion years, despite the mantle flow that accompanies plate tectonics. Cryosphere Geosphere Kola Superdeep Borehole Plate tectonics Solid Earth Chernicoff, Stanley, Whitney, earths Crust, Lithosphere and Asthenosphere Crust and Lithosphere
14.
Basalt
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Basalt is a common extrusive igneous rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of basalt flows. By definition, basalt is an igneous rock with generally 45-55% silica and less than 10% feldspathoid by volume. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains, the average density is 3.0 gm/cm3. Basalt is defined by its content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic minerals into hematite, although usually characterized as dark, basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured and these phenocrysts usually are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt. Basalt with a texture is called vesicular basalt, when the bulk of the rock is mostly solid. Gabbro is often marketed commercially as black granite and these ultramafic volcanic rocks, with silica contents below 45% are usually classified as komatiites. Agricola applied basalt to the black rock of the Schloßberg at Stolpen. Tholeiitic basalt is relatively rich in silica and poor in sodium, included in this category are most basalts of the ocean floor, most large oceanic islands, and continental flood basalts such as the Columbia River Plateau. Basalt rocks are in some cases classified after their content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalts have been distinguished in the Paraná and Etendeka traps and it has greater than 17% alumina and is intermediate in composition between tholeiite and alkali basalt, the relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. Alkali basalt is relatively poor in silica and rich in sodium and it is silica-undersaturated and may contain feldspathoids, alkali feldspar and phlogopite. Boninite is a form of basalt that is erupted generally in back-arc basins. Ocean island basalt Lunar basalt On Earth, most basalt magmas have formed by melting of the mantle. Basalt commonly erupts on Io, the third largest moon of Jupiter, and has formed on the Moon, Mars, Venus. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below, the mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene
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Seabed
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The seabed is the bottom of the ocean. Most of the oceans have a structure, created by common physical phenomena, mainly from tectonic movement. The mid-ocean ridge, as its name implies, is a rise through the middle of all the oceans. Typically a rift runs along the edge of this ridge, along tectonic plate edges there are typically oceanic trenches – deep valleys, created by the mantle circulation movement from the mid-ocean mountain ridge to the oceanic trench. Hotspot volcanic island ridges are created by volcanic activity, erupting periodically, in areas with volcanic activity and in the oceanic trenches there are hydrothermal vents – releasing high pressure and extremely hot water and chemicals into the typically freezing water around it. Deep ocean water is divided into layers or zones, each with features of salinity, pressure, temperature and marine life. Lying along the top of the plain is the abyssal zone. The hadal zone – which includes the oceanic trenches, lies between 6, 000–11,000 metres and is the deepest oceanic zone, the acronym mbsf meaning meters below the seafloor is a convention used for depths below the seafloor. Benthos is the community of organisms which live on, in, or near the seabed and this community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths. The benthic zone is the region on, in and immediately above the seabed, including the sediment surface. Benthos generally live in relationship with the substrate bottom. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, each area of the seabed has typical features such as common soil composition, typical topography, salinity of water layers above it, marine life, magnetic direction of rocks, and sedimentation. Seabed topography is flat where sedimentation is heavy and covers the tectonic features, marine life is abundant in the deep sea, especially around hydrothermal vents. Large deep sea communities of life have been discovered around black and white smokers—vents emitting chemicals toxic to humans. This marine life receives its energy both from the temperature difference and from chemosynthesis by bacteria. Brine pools are another seabed feature, usually connected to cold seeps, the seabed has been explored by submersibles such as Alvin and, to some extent, scuba divers with special equipment. The process that adds new material to the ocean floor is seafloor spreading. In recent years satellite images show a very clear mapping of the seabed, some childrens play songs include elements such as Theres a hole at the bottom of the sea, or A sailor went to sea
16.
Hydrothermal vent
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A hydrothermal vent is a fissure in a planets surface from which geothermally heated water issues. Hydrothermal vents are found near volcanically active places, areas where tectonic plates are moving apart, ocean basins. Hydrothermal vents exist because the earth is both active and has large amounts of water on its surface and within its crust. Common land types include hot springs, fumaroles and geysers, under the sea, hydrothermal vents may form features called black smokers. Chemosynthetic bacteria and archaea form the base of the chain, supporting diverse organisms, including giant tube worms, clams, limpets. Active hydrothermal vents are believed to exist on Jupiters moon Europa, and Saturns moon Enceladus, Hydrothermal vents in the deep ocean typically form along the mid-ocean ridges, such as the East Pacific Rise and the Mid-Atlantic Ridge. These are locations where two plates are diverging and new crust is being formed. The proportion of each varies from location to location, in contrast to the approximately 2 °C ambient water temperature at these depths, water emerges from these vents at temperatures ranging from 60 to as high as 464 °C. Due to the hydrostatic pressure at these depths, water may exist in either its liquid form or as a supercritical fluid at such temperatures. The critical point of water is 375 °C at a pressure of 218 atmospheres, however, introducing salinity into the fluid raises the critical point to higher temperatures and pressures. The critical point of seawater is 407 °C and 298.5 bars, accordingly, if a hydrothermal fluid with a salinity of 3.2 wt. % NaCl vents above 407 °C and 298.5 bars, furthermore, the salinity of vent fluids have been shown to vary widely due to phase separation in the crust. The critical point for lower salinity fluids is at lower temperature and pressure conditions than that for seawater, for example, a vent fluid with a 2.24 wt. % NaCl salinity has the point at 400 °C and 280.5 bars. Thus, water emerging from the hottest parts of some hydrothermal vents can be a supercritical fluid, examples of supercritical venting are found at several sites. Sister Peak vents low salinity phase-separated, vapor-type fluids, sustained venting was not found to be supercritical but a brief injection of 464 °C was well above supercritical conditions. A nearby site, Turtle Pits, was found to vent low salinity fluid at 407 °C, which is above the critical point of the fluid at that salinity. A vent site in the Cayman Trough named Beebe, which is the worlds deepest known hydrothermal site at ~5000 m below sea level, has shown sustained supercritical venting at 401 °C and 2.3 wt% NaCl
17.
Transform fault
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A transform fault or transform boundary, is a type of fault whose relative motion is predominantly horizontal, in either a sinistral or dextral direction. Furthermore, transform faults end abruptly and are connected on both ends to other faults, ridges, or subduction zones, Transform faults are the only type of strike-slip fault that can be classified as a plate boundary. The new class of faults, called transform faults, produce slip in the direction from what one would surmise from the standard interpretation of an offset geological feature. Slip along transform faults does not increase the distance between the ridges it separates, the distance remains constant in earthquakes because the ridges are spreading centers. This hypothesis was confirmed in a study of the fault plane solutions that showed the slip on transform faults points in the opposite direction than classical interpretation would suggest, Transform faults are closely related to transcurrent faults, and are commonly confused. In addition, transform faults have equal deformation across the fault line, while transcurrent faults have greater displacement in the middle of the fault zone. Finally, transform faults can form a plate boundary, while transcurrent faults cannot. The effect of a fault is to strain, which can be caused by compression, extension. Transform faults specifically relieve strain by transporting the strain between ridges or subduction zones, Transform faults also act as the plane of weakness allowing for the splitting in rift zones. Transform faults are commonly found linking segments of mid-oceanic ridges or spreading centres and these mid-oceanic ridges are where new seafloor is constantly created through the upwelling of new basaltic magma. With new seafloor being pushed and pulled out, the older seafloor slowly slides away from the mid-oceanic ridges toward the continents, although separated only by tens of kilometers, this separation between segments of the ridges causes portions of the seafloor to push past each other in opposing directions. This lateral movement of seafloors past each other is where transform faults are currently active, Transform faults move differently than a strike-slip fault at the mid-oceanic ridge. Evidence of this can be found in paleomagnetic striping on the seafloor, a paper written by Gerya theorizes that the creation of the transform faults between the ridges of the mid-oceanic ridge is attributed to rotated and stretched sections of the mid-oceanic ridge. This occurs over a period of time with the spreading center or ridge slowly deforming from a straight line to a curved line. Finally, fracturing along these planes forms transform faults, as this takes place, the fault changes from a normal fault with extensional stress to a strike slip fault with lateral stress. In the study done by Bonatti & Crane, peridotite and gabbro rocks were discovered in the edges of the transform ridges and these rocks are created deep inside the Earth’s mantle and then rapidly exhumed to the surface. This evidence helps to prove that new seafloor is being created at the mid-oceanic ridges, as previously stated, active transform faults are between two tectonic structures or faults. Fracture zones represent the active transform fault lines, which have since passed the active transform zone and are being pushed toward the continents
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Rift
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In geology, a rift is a linear zone where the Earths crust and lithosphere are being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben with normal faulting, where rifts remain above sea level they form a rift valley, which may be filled by water forming a rift lake. The axis of the area may contain volcanic rocks, and active volcanism is a part of many. Major rifts occur along the axis of most mid-ocean ridges. Failed rifts are the result of rifting that failed to continue to the point of break-up. Typically the transition from rifting to spreading develops at a junction where three converging rifts meet over a hotspot. Two of these evolve to the point of spreading, while the third ultimately fails. Most rifts consist of a series of segments that together form the linear zone characteristic of rifts. The individual rift segments have a dominantly half-graben geometry, controlled by a single basin-bounding fault, segment lengths vary between rifts, depending on the elastic thickness of the lithosphere. Areas of thick colder lithosphere, such as the Baikal Rift have segment lengths in excess of 80 km, while in areas of warmer thin lithosphere, segment lengths may be less than 30 km. Along the axis of the rift the position, and in cases the polarity. Segment boundaries often have a complex structure and generally cross the rift axis at a high angle. These segment boundary zones accommodate the differences in fault displacement between the segments and are known as accommodation zones. Accommodation zones may be located where older crustal structures intersect the rift axis, in the Gulf of Suez rift, the Zaafarana accommodation zone is located where a shear zone in the Arabian-Nubian Shield meets the rift. At the onset of rifting, the part of the lithosphere starts to extend on a series of initially unconnected normal faults. In subaerial rifts, drainage at this stage is generally internal, as the rift evolves, some of the individual fault segments grow, eventually becoming linked together to form the larger bounding faults. Subsequent extension becomes concentrated on these faults, the longer faults and wider fault spacing leads to more continuous areas of fault-related subsidence along the rift axis. Significant uplift of the rift shoulders develops at this stage, strongly influencing drainage, during rifting, as the crust is thinned, the Earths surface subsides and the Moho becomes correspondingly raised
19.
East African Rift
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The East African Rift is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago, in the past, it was considered to be part of a larger Great Rift Valley that extended north to Asia Minor. As extension continues, lithospheric rupture will occur within 10 million years, the Somalian plate will break off, a series of distinct rift basins, the East African Rift System extends over thousands of kilometers. The EAR consists of two main branches, the Eastern Rift Valley includes the Main Ethiopian Rift, running eastward from the Afar Triple Junction, which continues south as the Kenyan Rift Valley. The Western Rift Valley includes the Albertine Rift, and farther south, to the north of the Afar Triple Junction, the rift follows one of two paths, west to the Red Sea Rift or east to the Aden Ridge in the Gulf of Aden. The EAR runs from the Afar Triple Junction in the Afar Triangle of Ethiopia through eastern Africa, the EAR transects through Ethiopia, Kenya, Uganda, Rwanda, Burundi, Zambia, Tanzania, Malawi and Mozambique. The Davie Ridge ranges between 30–120 km wide, with a west facing scarp along the half of its length that rises up to 2300 m above the sea floor. Its movement is concurrent with the EAR, over time, many theories have tried to clarify the evolution of the East African Rift. In 1972 it was proposed that the EAR was not caused by tectonic activity, others proposed an African superplume causing mantle deformation. However, the varying geochemical signatures of a suite of Ethiopian lavas suggest multiple plume sources, at least one of deep mantle origin, additionally, the subject of deep-rooted mantle plumes is still a matter of controversy, and therefore cannot be confirmed. The most recent and accepted view is the theory put forth in 2009, at that time it was suggested that lithospheric thinning generated volcanic activity, further increasing the magmatic processes at play such as intrusions and numerous small plumes. These processes further thin the lithosphere in saturated areas, forcing the thinning lithosphere to behave like a mid-ocean ridge, prior to rifting, enormous continental flood basalts erupted on the surface and uplift of the Ethiopian, Somalian, and East African plateaus occurred. The first stage of rifting of the EAR is characterized by rift localization, periods of extension alternated with times of relative inactivity. There was also the reactivation of a weakness in the crust, a suture zone of multiple cratons, displacement along large boundary faults. The second stage of rifting is characterized by the deactivation of large boundary faults, the development of internal fault segments, today, the narrow rift segments of the East African Rift system form zones of localized strain. These rifts are the result of the actions of numerous faults which are typical of all tectonic rift zones. The African continental crust is generally cool and strong, many cratons are found throughout the EAR, such as the Tanzania and Kaapvaal cratons. The cratons are thick, and have survived for billions of years with little tectonic activity and they are characterized by greenstone belts, tonalites, and other high-grade metamorphic lithologies
20.
Isostasy
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Isostasy is the state of gravitational equilibrium between Earths crust and mantle such that the crust floats at an elevation that depends on its thickness and density. This concept is invoked to explain how different topographic heights can exist at Earths surface, when a certain area of Earths crust reaches the state of isostasy, it is said to be in isostatic equilibrium. Isostasy does not upset equilibrium but instead restores it and it is generally accepted that Earth is a dynamic system that responds to loads in many different ways. However, isostasy provides an important view of the processes that are happening in areas that are experiencing vertical movement. In the simplest example, isostasy is the principle of buoyancy wherein an object immersed in a fluid is buoyed with a equal to the weight of the displaced fluid. The general term isostasy was coined in the year 1889 by the American geologist Clarence Dutton, the Vening Meinesz, or flexural isostasy model – where the lithosphere acts as an elastic plate and its inherent rigidity distributes local topographic loads over a broad region by bending. Airy and Pratt isostasy are statements of buoyancy, whereas flexural isostasy is a statement of buoyancy when deflecting a sheet of finite elastic strength. The basis of the model is Pascals law, and particularly its consequence that, within a fluid in static equilibrium, in other words, h1⋅ρ1 = h2⋅ρ2 = h3⋅ρ3 =. This hypothesis was suggested to explain how large topographic loads such as seamounts could be compensated by regional rather than local displacement of the lithosphere. When large amounts of sediment are deposited on a particular region, similarly, when large amounts of material are eroded away from a region, the land may rise to compensate. Therefore, as a range is eroded, the range rebounds upwards to be eroded further. An analogy may be made with an iceberg—it always floats with a proportion of its mass below the surface of the water. If more ice is added to the top of the iceberg, if a layer of ice is somehow sliced off the top of the iceberg, the remaining iceberg will rise. Similarly, Earths lithosphere floats in the asthenosphere, when continents collide, the continental crust may thicken at their edges in the collision. If this happens, much of the thickened crust may move downwards rather than up as with the iceberg analogy, the idea of continental collisions building mountains up is therefore rather a simplification. Instead, the crust thickens and the part of the thickened crust may become a mountain range. However, some continental collisions are far more complex than this, the formation of ice sheets can cause Earths surface to sink. Conversely, isostatic rebound is observed in areas once covered by ice sheets that have now melted, such as around the Baltic Sea
21.
Triple junction
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A triple junction is the point where the boundaries of three tectonic plates meet. Of the many types of triple junction only a few are stable through time. The first scientific paper detailing the triple junction concept was published in 1969 by W. Jason Morgan, Dan McKenzie, the term had traditionally been used for the intersection of three divergent boundaries or spreading ridges. These three divergent boundaries ideally meet at near 120° angles, in plate tectonics theory during the breakup of a continent, three divergent boundaries form, radiating out from a central point. One of these divergent plate boundaries fails and the two continue spreading to form an ocean. The NE-trending Benue Trough is the arm of this junction. In the years since, the term triple-junction has come to refer to any point where three tectonic plates meet, the junction of the Red Sea, the Gulf of Aden and the East African Rift centered in the Afar Triangle is the only Ridge-Ridge-Ridge triple junction above sea level. The Rodrigues Triple Point is a R-R-R triple junction in the southern Indian Ocean, where the African, the Indo-Australian, the Galapagos Triple Junction is an R-R-R triple junction where the Nazca, the Cocos, and the Pacific Plates meet. The East Pacific Rise extends north and south from this junction and this example is made more complex by the Galapagos Microplate which is a small separate plate on the rise just to the southeast of the triple junction. Chiapas coast off Tapachula where Guatemala, North America and Pacific join and this is pushed eastward by the Cocos plate. On the west coast of North America is another triple junction offshore of Cape Mendocino. To the south, the San Andreas Fault, a fault and transform plate boundary, separates the Pacific Plate. To the north lies the Cascadia subduction zone, where a section of the Juan de Fuca Plate called the Gorda Plate is being subducted under the North American Plate, another transform fault, the Mendocino Fault, runs along the boundary between the Pacific Plate and the Gorda Plate. Where the three intersect is the active, F-F-T Mendocino Triple Junction. The Amurian Plate, the Okhotsk Plate, and the Philippine Sea Plate meet in Japan near Mt. Fuji. The Azores Triple Junction is a triple junction where the boundaries of three tectonic plates intersect, the North American Plate, the Eurasian Plate and the African Plate. The Boso Triple Junction offshore Japan is a T-T-T triple junction between the Okhotsk Plate, Pacific Plate and Philippine Sea Plate, the North Sea is located at the extinct triple junction of three former continental plates of the Palaeozoic era, Avalonia, Laurentia and Baltica. The properties of triple junctions are most easily understood from the purely kinematic point of view where the plates are rigid, no knowledge of the Earths interior or the geological details of the crust are then needed
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Passive margin
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A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere, Continental rifting creates new ocean basins. Eventually the continental rift forms a ridge and the locus of extension moves away from the continent-ocean boundary. The transition between the continental and oceanic lithosphere that was created by rifting is known as a passive margin. Passive margins are found at every ocean and continent boundary that is not marked by a fault or a subduction zone. Passive margins define the region around the Atlantic Ocean, Arctic Ocean, and western Indian Ocean and they are also found on the east coast of North America and South America, in western Europe and most of Antarctica. East Asia also contains some passive margins and this refers to whether a crustal boundary between oceanic lithosphere and continental lithosphere is a plate boundary or not. Active margins are found on the edge of a continent where subduction occurs and these are often marked by uplift and volcanic mountain belts on the continental plate. Less often there is a fault, as defines the southern coastline of W. Africa. Most of the eastern Indian Ocean and nearly all of the Pacific Ocean margin are examples of active margins, while a weld between oceanic and continental lithosphere is called a passive margin, it is not an inactive margin. Active subsidence, sedimentation, growth faulting, pore formation and migration are all active processes on passive margins. Passive margins are only passive in that they are not active plate boundaries, Passive margins consist of both onshore coastal plain and offshore continental shelf-slope-rise triads. Coastal plains are dominated by fluvial processes, while the continental shelf is dominated by deltaic. The great rivers drain across passive margins, extensive estuaries are common on mature passive margins. Although there are kinds of passive margins, the morphologies of most passive margins are remarkably similar. Typically they consist of a shelf, continental slope, continental rise. The morphological expression of features are largely defined by the underlying transitional crust. Passive margins defined by a fluvial sediment budget and those dominated by coral
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Red Sea
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The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait, to the north lie the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez. The Red Sea is a Global 200 ecoregion, the sea is underlain by the Red Sea Rift which is part of the Great Rift Valley. The Red Sea has an area of roughly 438,000 km2, is about 2250 km long and. It has a depth of 2211 m in the central median trench. However, there are also extensive shallow shelves, noted for their marine life, the sea is the habitat of over 1,000 invertebrate species, and 200 soft and hard corals. It is the worlds northernmost tropical sea, the International Hydrographic Organization defines the limits of the Red Sea as follows, On the North. The Southern limits of the Gulfs of Suez and Aqaba, a line joining Husn Murad and Ras Siyyan. Red Sea is a translation of the Greek Erythra Thalassa, Latin Mare Rubrum, Arabic, البحر الأحمر. Al-Baḥr Al-Aḥmar, Somali Badda Cas and Tigrinya Qeyyiḥ bāḥrī, the name of the sea may signify the seasonal blooms of the red-coloured Trichodesmium erythraeum near the waters surface. A theory favored by modern scholars is that the name red is referring to the direction south. The basis of this theory is that some Asiatic languages used color words to refer to the cardinal directions, herodotus on one occasion uses Red Sea and Southern Sea interchangeably. Historically, it was known to western geographers as Mare Mecca. Some ancient geographers called the Red Sea the Arabian Gulf or Gulf of Arabia. C, in that version, the Yam Suph is translated as Erythra Thalassa. The Red Sea is one of four seas named in English after common color terms — the others being the Black Sea, the White Sea and the Yellow Sea. The direct rendition of the Greek Erythra thalassa in Latin as Mare Erythraeum refers to the part of the Indian Ocean. The earliest known exploration of the Red Sea was conducted by ancient Egyptians, one such expedition took place around 2500 BC, and another around 1500 BC. Both involved long voyages down the Red Sea, historically, scholars argued whether these trips were possible
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Ethiopia
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Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It shares borders with Eritrea to the north and northeast, Djibouti and Somalia to the east, Sudan and South Sudan to the west, and Kenya to the south. With nearly 100 million inhabitants, Ethiopia is the most populous landlocked country in the world and it occupies a total area of 1,100,000 square kilometres, and its capital and largest city is Addis Ababa. Some of the oldest evidence for modern humans has been found in Ethiopia. It is widely considered as the region from modern humans first set out for the Middle East. According to linguists, the first Afroasiatic-speaking populations settled in the Horn region during the ensuing Neolithic era, tracing its roots to the 2nd millennium BC, Ethiopia was a monarchy for most of its history. During the first centuries AD, the Kingdom of Aksum maintained a unified civilization in the region, subsequently, many African nations adopted the colors of Ethiopias flag following their independence. It was the first independent African member of the 20th-century League of Nations, Ethiopias ancient Geez script, also known as Ethiopic, is one of the oldest alphabets still in use in the world. The Ethiopian calendar, which is seven years and three months behind the Gregorian calendar, co-exists alongside the Borana calendar. A slight majority of the population adheres to Christianity, while around a third follows Islam, the country is the site of the Migration to Abyssinia and the oldest Muslim settlement in Africa at Negash. A substantial population of Ethiopian Jews, known as Bete Israel, resided in Ethiopia until the 1980s, Ethiopia is a multilingual nation with around 80 ethnolinguistic groups, the four largest of which are the Oromiffa, Amhara, Somali, and Tigrayans. Most people in the country speak Afroasiatic languages of the Cushitic or Semitic branches, additionally, Omotic languages are spoken by ethnic minority groups inhabiting the southern regions. Nilo-Saharan languages are spoken by the nations Nilotic ethnic minorities. Ethiopia is the place of origin for the coffee bean which originated from the place called Kefa and it is a land of natural contrasts, with its vast fertile West, jungles, and numerous rivers, and the worlds hottest settlement of Dallol in its north. The Ethiopian Highlands are Africas largest continuous mountain ranges, and Sof Omar Caves contain Africas largest cave, Ethiopia has the most UNESCO World Heritage Sites in Africa. Ethiopia is one of the members of the UN, the Group of 24, the Non-Aligned Movement, G-77. In the 1970s and 1980s, Ethiopia suffered from civil wars, the country has begun to recover recently however, and now has the largest economy in East Africa and Central Africa. According to Global Fire Power, Ethiopia has the 42nd most powerful military in the world, the origin of the word Ethiopia is uncertain
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Afar Region
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The Afar Regional State is one of the nine regional states of Ethiopia, and is the homeland of the Afar people. Formerly known as Region 2, its new capital as of 2007 is the recently constructed city of Semera, which lies on the paved Awash–Assab highway. The Afar Triangle, the part of which is the Danakil Depression, is part of the Great Rift Valley of Ethiopia. It has the lowest point in Ethiopia and one of the lowest in Africa, the southern part of the region consists of the valley of the Awash River, which empties into a string of lakes along the Ethiopian-Djibouti border. Other notable landmarks include the Awash and Yangudi Rassa National Parks. 32% of the population, with an estimated area of 96,707 square kilometers, this region has an estimated density of 14.38 people per square kilometer. Ethnic groups include Afar, Amhara, Argobba Tigrinya people, Oromo, Welayta,95. 3% of the population is Muslim and 4. 7% is Christian. In the previous census, conducted in 1994, the population was reported to be 1,106,383 of whom 626,839 were men and 479,544 women. The major ethnic compositions were the Afar, Amhara, Argobba, Tigrayans, Oromo, Welayta, in the urban areas, the Amhara ethnicity were the most numerous, placing the Afar in second place, followed by Tigrinnya, Oromo, Argobba, and Welayta. 95. 6% of the population were Muslim,3. 9% Orthodox Christians,0. 4% Protestants, Afar is predominantly spoken in the region and is the working language of the state. Other languages with a significant number of speakers in the state include Amharic, Tigrinnya, Argobba, Wolaitigna, and Oromifa. According to the CSA, as of 2004,48. 57% of the population had access to safe drinking water. Afar Depression, Erta Ale active volcano, Awash National Park, Yangudi Rassa National Park, Hadar, the hot springs, Afar culture and cultural games are other attraction areas. In 2005, a giant rift was formed in just a few days, the rift opened when the Dabbahu Volcano, situated in the north of the region, erupted. The crack forming is thought to be part of the process in which the Arabian Plate and African plates are moving apart. This new crack,500 metres long, and 60 metres deep, opened when the lava from the volcano flowed underground. The Afar Depression, a tectonic triple junction is found in the Afar Regional State. This geologic feature is one of great active volcanic areas. Due to this activity the floor of the depression is composed of lava
26.
Sea level
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Mean sea level is an average level of the surface of one or more of Earths oceans from which heights such as elevations may be measured. A common and relatively straightforward mean sea-level standard is the midpoint between a low and mean high tide at a particular location. Sea levels can be affected by factors and are known to have varied greatly over geological time scales. The careful measurement of variations in MSL can offer insights into ongoing climate change, the term above sea level generally refers to above mean sea level. Precise determination of a sea level is a difficult problem because of the many factors that affect sea level. Sea level varies quite a lot on several scales of time and this is because the sea is in constant motion, affected by the tides, wind, atmospheric pressure, local gravitational differences, temperature, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point, for example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point. One measures the values of MSL in respect to the land, hence a change in MSL can result from a real change in sea level, or from a change in the height of the land on which the tide gauge operates. In the UK, the Ordnance Datum is the sea level measured at Newlyn in Cornwall between 1915 and 1921. Prior to 1921, the datum was MSL at the Victoria Dock, in Hong Kong, mPD is a surveying term meaning metres above Principal Datum and refers to height of 1. 230m below the average sea level. In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and it is used for a part of continental Europe and main part of Africa as official sea level. Elsewhere in Europe vertical elevation references are made to the Amsterdam Peil elevation, satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES, TOPEX/Poseidon was followed by Jason-1 in 2001, height above mean sea level is the elevation or altitude of an object, relative to the average sea level datum. It is also used in aviation, where some heights are recorded and reported with respect to sea level, and in the atmospheric sciences. An alternative is to base height measurements on an ellipsoid of the entire Earth, in aviation, the ellipsoid known as World Geodetic System 84 is increasingly used to define heights, however, differences up to 100 metres exist between this ellipsoid height and mean tidal height. The alternative is to use a vertical datum such as NAVD88. When referring to geographic features such as mountains on a topographic map, the elevation of a mountain denotes the highest point or summit and is typically illustrated as a small circle on a topographic map with the AMSL height shown in metres, feet or both. In the rare case that a location is below sea level, for one such case, see Amsterdam Airport Schiphol
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Petroleum
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Petroleum is a naturally occurring, yellow-to-black liquid found in geological formations beneath the Earths surface, which is commonly refined into various types of fuels. Components of petroleum are separated using a technique called fractional distillation and it consists of hydrocarbons of various molecular weights and other organic compounds. The name petroleum covers both naturally occurring unprocessed crude oil and petroleum products that are made up of refined crude oil. A fossil fuel, petroleum is formed when large quantities of dead organisms, usually zooplankton and algae, are buried underneath sedimentary rock, Petroleum has mostly been recovered by oil drilling. Drilling is carried out studies of structural geology, sedimentary basin analysis. Petroleum is used in manufacturing a variety of materials. Concern over the depletion of the earths finite reserves of oil, the burning of fossil fuels plays the major role in the current episode of global warming. The word petroleum comes from Greek, πέτρα for rocks and Greek, the term was found in 10th-century Old English sources. It was used in the treatise De Natura Fossilium, published in 1546 by the German mineralogist Georg Bauer, Petroleum, in one form or another, has been used since ancient times, and is now important across society, including in economy, politics and technology. Great quantities of it were found on the banks of the river Issus, ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper levels of their society. By 347 AD, oil was produced from bamboo-drilled wells in China, early British explorers to Myanmar documented a flourishing oil extraction industry based in Yenangyaung that, in 1795, had hundreds of hand-dug wells under production. The mythological origins of the oil fields at Yenangyaung, and its hereditary monopoly control by 24 families, Pechelbronn is said to be the first European site where petroleum has been explored and used. The still active Erdpechquelle, a spring where petroleum appears mixed with water has been used since 1498, Oil sands have been mined since the 18th century. In Wietze in lower Saxony, natural asphalt/bitumen has been explored since the 18th century, both in Pechelbronn as in Wietze, the coal industry dominated the petroleum technologies. In 1848 Young set up a small business refining the crude oil, Young eventually succeeded, by distilling cannel coal at a low heat, in creating a fluid resembling petroleum, which when treated in the same way as the seep oil gave similar products. The production of oils and solid paraffin wax from coal formed the subject of his patent dated 17 October 1850. In 1850 Young & Meldrum and Edward William Binney entered into partnership under the title of E. W. Binney & Co. at Bathgate in West Lothian, the worlds first oil refinery was built in 1856 by Ignacy Łukasiewicz. The demand for petroleum as a fuel for lighting in North America, edwin Drakes 1859 well near Titusville, Pennsylvania, is popularly considered the first modern well
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Oceanic basin
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In hydrology, an oceanic basin may be anywhere on Earth that is covered by seawater, but geologically ocean basins are large geologic basins that are below sea level. Older references consider the oceanic basins to be the complement to the continents, with dominating the latter. Earth is the known planet in the solar system where hypsography is characterized by different kinds of crust, oceanic crust. Oceans cover 70% of the Earths surface, because oceans lie lower than continents, the former serve as sedimentary basins that collect sediment eroded from the continents, known as clastic sediments, as well as precipitation sediments. Ocean basins also serve as repositories for the skeletons of carbonate- and silica-secreting organisms such as reefs, diatoms, radiolarians. Geologically, a basin may be actively changing size or may be relatively, tectonically inactive. The elements of an active - and growing - oceanic basin include an elevated mid-ocean ridge, the elements of an active oceanic basin often include the oceanic trench associated with a subduction zone. The Atlantic ocean and the Arctic ocean are good examples of active, growing oceanic basins, the Pacific Ocean is also an active, shrinking oceanic basin, even though it has both spreading ridge and oceanic trenches. Perhaps the best example of an oceanic basin is the Gulf of Mexico. The Aleutian Basin is another example of an inactive oceanic basin. The Japan Basin in the Sea of Japan which formed in the Miocene, is still active although recent changes have been relatively mild. List of abyssal plains and oceanic basins List of oceanic landforms Solid Earth Wright, John et al
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Niger Delta
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The Niger Delta is the delta of the Niger River sitting directly on the Gulf of Guinea on the Atlantic Ocean in Nigeria. Of all the states that the covers, only Cross River is not an oil-producing state. Niger Delta is a densely populated region sometimes called the Oil Rivers because it was once a major producer of palm oil. The area was the British Oil Rivers Protectorate from 1885 until 1893, the delta is a petroleum-rich region, and has been the centre of international controversy over pollution, corruption, and human rights violations. The Niger Delta, as now defined officially by the Nigerian government, extends over about 70,000 km2, historically and cartographically, it consists of present-day Bayelsa, Delta, and Rivers States. In 2000, however, Obasanjos regime included Abia, Akwa-Ibom, Cross River State, Edo, Imo, the Niger Delta, and the South South geopolitical zone are two different entities. The Niger Delta separates the Bight of Benin from the Bight of Biafra within the larger Gulf of Guinea, the area was the British Oil Rivers Protectorate from 1885 until 1893, when it was expanded and became the Niger Coast Protectorate. The core Niger Delta later became a part of the region of Nigeria. The majority of the people were those from the colonial Calabar and Ogoja divisions, the present-day Ogoja, Annang, Ibibio, Oron, Efik, the National Council of Nigeria and Cameroon was the ruling political party of the region. The NCNC later became the National Convention of Nigerian Citizens, after western Cameroon decided to separate from Nigeria, the ruling party of eastern Nigeria did not seek to preclude the separation and even encouraged it. The then Eastern Region had the second, fourth and fifth largest ethnic groups in the country the Igbo, the Ijaw and the Ibibio after the Hausa-Fulani and the Yoruba. In 1953, the old eastern region had a crisis due to the expulsion of professor Eyo Ita from office by the majority Igbo tribe of the old eastern region. Ita, an Efik man from Calabar, was one of the nationalists for Nigerian independence. The struggle for the creation of the COR state continued and was an issue concerning the status of minorities in Nigeria during debates in Europe on Nigerian independence. The aftermath of the 1961 plebiscite has led to a dispute between Cameroon and Nigeria over the territory of Bakassi. A new phase of the saw the declaration of an Independent Niger Delta Republic by Isaac Adaka Boro during Nigerian president Ironsis administration. Also just before the Nigerian civil war, Southeastern State of Nigeria was created, which had the colonial Calabar division, and colonial Ogoja division. Southeastern state and River state became two states for the minorities of the old eastern region, and the majority Igbo of the old eastern region had a state called East Central state
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Subduction
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Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced or sinks due to gravity into the mantle. Regions where this occurs are known as subduction zones. Rates of subduction are typically in centimeters per year, with the rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Plates include both oceanic crust and continental crust, stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere. That is, the lithosphere is always oceanic while the overriding lithosphere may or may not be oceanic. Subduction zones are sites that have a rate of volcanism, earthquakes. Subduction zones are sites of convective downwelling of Earths lithosphere, subduction zones exist at convergent plate boundaries where one plate of oceanic lithosphere converges with another plate. The descending slab, the plate, is over-ridden by the leading edge of the other plate. The slab sinks at an angle of approximately twenty-five to forty-five degrees to Earths surface and this sinking is driven by the temperature difference between the subducting oceanic lithosphere and the surrounding mantle asthenosphere, as the colder oceanic lithosphere is, on average, denser. At a depth of approximately 80–120 kilometers, the basalt of the oceanic crust is converted to a rock called eclogite. At that point, the density of the oceanic crust increases and provides additional negative buoyancy and it is at subduction zones that Earths lithosphere, oceanic crust, sedimentary layers and some trapped water are recycled into the deep mantle. Earth is so far the only planet where subduction is known to occur, subduction is the driving force behind plate tectonics, and without it, plate tectonics could not occur. Subduction zones dive down into the mantle beneath 55,000 kilometers of convergent plate margins, subduction zones burrow deeply but are imperfectly camouflaged, and geophysics and geochemistry can be used to study them. Not surprisingly, the shallowest portions of subduction zones are known best, subduction zones are strongly asymmetric for the first several hundred kilometers of their descent. They start to go down at oceanic trenches and their descents are marked by inclined zones of earthquakes that dip away from the trench beneath the volcanoes and extend down to the 660-kilometer discontinuity. Subduction zones are defined by the array of earthquakes known as the Wadati–Benioff zone after the two scientists who first identified this distinctive aspect. Subduction zone earthquakes occur at greater depths than elsewhere on Earth, such deep earthquakes may be driven by deep phase transformations, thermal runaway, the subducting basalt and sediment are normally rich in hydrous minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as the slab bends downward
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Ring of Fire
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The Ring of Fire is a major area in the basin of the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur. In a 40,000 km horseshoe shape, it is associated with a continuous series of oceanic trenches, volcanic arcs. The Ring of Fire is sometimes called the circum-Pacific belt, about 90% of the worlds earthquakes and 81% of the worlds largest earthquakes occur along the Ring of Fire. The next most seismically active region is the Alpide belt, which extends from Java to the northern Atlantic Ocean via the Himalayas, all but three of the worlds 25 largest volcanic eruptions of the last 11,700 years occurred at volcanoes in the Ring of Fire. The Ring of Fire is a result of plate tectonics. The eastern section of the ring is the result of the Nazca Plate, the Cocos Plate is being subducted beneath the Caribbean Plate, in Central America. A portion of the Pacific Plate and the small Juan de Fuca Plate are being subducted beneath the North American Plate, along the northern portion, the northwestward-moving Pacific plate is being subducted beneath the Aleutian Islands arc. Farther west, the Pacific plate is being subducted along the Kamchatka Peninsula arcs on south past Japan. Indonesia lies between the Ring of Fire along the islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Flores. The famous and very active San Andreas Fault zone of California is a fault which offsets a portion of the East Pacific Rise under southwestern United States. The motion of the fault generates numerous small earthquakes, at times a day. Bolivia hosts numerous active and extinct volcanoes across its territory, the active volcanoes are located in western Bolivia where they make up the Cordillera Occidental, the western limit of the Altiplano plateau. Many of the volcanoes are international mountains shared with Chile. The Central Volcanic Zone is a major upper Cenozoic volcanic province, apart from Andean volcanoes, the geology of Bolivia hosts the remnants of ancient volcanoes around the Precambrian Guaporé Shield in the eastern part of the country. The volcanoes in Chile are monitored by the National Geology and Mining Service Earthquake activity in Chile is related to subduction of the Nazca Plate to the east, Chile notably holds the record for the largest earthquake ever recorded, the 1960 Valdivia earthquake. Villarrica, one of Chiles most active volcanoes, rises above Villarrica Lake and it is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene, more than 0.9 million years ago, a 2-km-wide postglacial caldera is located at the base of the presently active, dominantly basaltic-to-andesitic cone at the northwest margin of the Pleistocene caldera. About 25 scoria cones dot Villaricas flanks, lahars from the glacier-covered volcanoes have damaged towns on its flanks
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East Pacific Rise
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The East Pacific Rise is a mid-oceanic ridge, a divergent tectonic plate boundary located along the floor of the Pacific Ocean. It separates the Pacific Plate to the west from the North American Plate, the Rivera Plate, the Cocos Plate, the Nazca Plate, and the Antarctic Plate. Much of the lies about 3200 km off the South American coast and rises about 1. The oceanic crust is moving away from the East Pacific Rise to either side, near Easter Island the rate is over 15 cm per year which is the fastest in the world but it is lower at about 6 cm at the north end. On the eastern side of the rise the eastward moving Cocos and Nazca plates meet the westward moving South American Plate, the belt of volcanoes along the Andes and the arc of volcanoes through Central America and Mexico are the direct results of this collision. Due east of the Baja California Peninsula, the Rise is sometimes referred to as the Gulf of California Rift Zone, in this area, newly formed oceanic crust is intermingled with rifted continental crust originating from the North American Plate. The southern extension of the East Pacific Rise merges with the Southeast Indian Ridge at the Macquarie Triple Junction south of New Zealand, along the East Pacific Rise the hydrothermal vents called black smokers were first discovered and have been extensively studied. These vents are forming volcanogenic massive sulfide ore deposits on the ocean floor, many strange deep-water creatures have been found here. The southern stretch of the East Pacific Rise is one of the sections of the Earths mid-ocean ridge system. East Pacific Rise 2004 – Scripps Institution of Oceanography Columbia University Researchers Find Key to the Formation of New Seafloor Spreading Centers – Columbia University
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Atlantic Ocean
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The Atlantic Ocean is the second largest of the worlds oceans with a total area of about 106,460,000 square kilometres. It covers approximately 20 percent of the Earths surface and about 29 percent of its surface area. It separates the Old World from the New World, the Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Eurasia and Africa to the east, and the Americas to the west. The Equatorial Counter Current subdivides it into the North Atlantic Ocean, in contrast, the term Atlantic originally referred specifically to the Atlas Mountains in Morocco and the sea off the Strait of Gibraltar and the North African coast. The Greek word thalassa has been reused by scientists for the huge Panthalassa ocean that surrounded the supercontinent Pangaea hundreds of years ago. The term Aethiopian Ocean, derived from Ancient Ethiopia, was applied to the Southern Atlantic as late as the mid-19th century, many Irish or British people refer to the United States and Canada as across the pond, and vice versa. The Black Atlantic refers to the role of ocean in shaping black peoples history. Irish migration to the US is meant when the term The Green Atlantic is used, the term Red Atlantic has been used in reference to the Marxian concept of an Atlantic working class, as well as to the Atlantic experience of indigenous Americans. Correspondingly, the extent and number of oceans and seas varies, the Atlantic Ocean is bounded on the west by North and South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea, to the east, the boundaries of the ocean proper are Europe, the Strait of Gibraltar and Africa. In the southeast, the Atlantic merges into the Indian Ocean, the 20° East meridian, running south from Cape Agulhas to Antarctica defines its border. In the 1953 definition it extends south to Antarctica, while in later maps it is bounded at the 60° parallel by the Southern Ocean, the Atlantic has irregular coasts indented by numerous bays, gulfs, and seas. Including these marginal seas the coast line of the Atlantic measures 111,866 km compared to 135,663 km for the Pacific. Including its marginal seas, the Atlantic covers an area of 106,460,000 km2 or 23. 5% of the ocean and has a volume of 310,410,900 km3 or 23. 3%. Excluding its marginal seas, the Atlantic covers 81,760,000 km2 and has a volume of 305,811,900 km3, the North Atlantic covers 41,490,000 km2 and the South Atlantic 40,270,000 km2. The average depth is 3,646 m and the maximum depth, the bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge. It runs from 87°N or 300 km south of the North Pole to the subantarctic Bouvet Island at 42°S, the MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above 2000 m along most of its length, the MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the other
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Western Interior Seaway
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The ancient sea stretched from the Gulf of Mexico and through the middle of the modern-day countries of the United States and Canada, meeting with the Arctic Ocean to the north. At its largest, it was 2,500 feet deep,600 miles wide, the Seaway was created as the Farallon tectonic plate subducted under the North American Plate during the Cretaceous. As plate convergence proceeded, the younger and more buoyant lithosphere of the Farallon Plate subducted at a shallow angle, in what is known as a flat slab. This shallowly subducting slab exerted traction on the base of the lithosphere, pulling it down, in the south, the Gulf of Mexico was an extension of the Tethys Sea, which met with the Mowry Sea in the late Cretaceous, forming the complete Seaway. At its largest, the Western Interior Seaway stretched from the Rockies east to the Appalachians, at its deepest, it may have been only 800 or 900 metres deep, shallow in terms of seas. Two great continental watersheds drained into it from east and west, diluting its waters, there was little sedimentation on the eastern shores of the Seaway, the western boundary, however, consisted of a thick clastic wedge eroded eastward from the Sevier orogenic belt. The western shore was thus highly variable, depending on variations in sea level, widespread carbonate deposition suggests that the Seaway was warm and tropical, with abundant calcareous algae. Remnants of these deposits are found throughout the state of Kansas, one prominent example is Monument Rocks, an exposed chalk formation towering 70 feet over the surrounding range land. It is designated a National Natural Landmark and one of the Eight Wonders of Kansas and it is located 25 miles south of Oakley, Kansas. At a few times during the late Cretaceous the Western Interior Seaway went through periods of anoxia, where the water was devoid of oxygen. The Western Interior Seaway divided across the Dakotas and retreated south towards the Gulf of Mexico and this shrunken, regressive phase of the Western Interior Seaway is sometimes called the Pierre Seaway. During the early Paleocene, parts of the Western Interior Seaway still occupied areas of the Mississippi Embayment, later transgression, however, was associated with the Cenozoic Tejas sequence, rather than with the previous event responsible for the Seaway. The Western Interior Seaway was a sea, filled with abundant marine life. Interior Seaway denizens included predatory marine reptiles such as plesiosaurs, icthyornis shared the sky with large pterosaurs such as Nyctosaurus and Pteranodon. Pteranodon fossils are common and it was probably a major component of the surface ecosystem. On the bottom, the giant clam Inoceramus left common fossilized shells in the Pierre Shale and this clam had a thick shell paved with prisms of calcite deposited perpendicular to the surface, giving it a pearly luster in life
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North America
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North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be considered a subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16. 5% of the land area. North America is the third largest continent by area, following Asia and Africa, and the fourth by population after Asia, Africa, and Europe. In 2013, its population was estimated at nearly 565 million people in 23 independent states, or about 7. 5% of the worlds population, North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge. The so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago, the Classic stage spans roughly the 6th to 13th centuries. The Pre-Columbian era ended with the migrations and the arrival of European settlers during the Age of Discovery. Present-day cultural and ethnic patterns reflect different kind of interactions between European colonists, indigenous peoples, African slaves and their descendants, European influences are strongest in the northern parts of the continent while indigenous and African influences are relatively stronger in the south. Because of the history of colonialism, most North Americans speak English, Spanish or French, the Americas are usually accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass previously unknown by Europeans. In 1507, Waldseemüller produced a map, in which he placed the word America on the continent of South America. He explained the rationale for the name in the accompanying book Cosmographiae Introductio, for Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespuccis name, but in its feminine form America, following the examples of Europa, Asia and Africa. Later, other mapmakers extended the name America to the continent, In 1538. Some argue that the convention is to use the surname for naming discoveries except in the case of royalty, a minutely explored belief that has been advanced is that America was named for a Spanish sailor bearing the ancient Visigothic name of Amairick. Another is that the name is rooted in a Native American language, the term North America maintains various definitions in accordance with location and context. In Canadian English, North America may be used to refer to the United States, alternatively, usage sometimes includes Greenland and Mexico, as well as offshore islands
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Gulf of Mexico
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The Gulf of Mexico is an ocean basin largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. The U. S. states of Alabama, Florida, Louisiana, Mississippi and Texas border the Gulf on the north, Atlantic and Pacific coasts, or sometimes the south coast, in juxtaposition to the Great Lakes region being the north coast. One of the seven main areas is the Gulf of Mexico basin. The Gulf of Mexico formed approximately 300 million years ago as a result of plate tectonics, the Gulfs basin is roughly oval and is approximately 810 nautical miles wide and floored by sedimentary rocks and recent sediments. It is connected to part of the Atlantic Ocean through the Florida Straits between the U. S. and Cuba, and with the Caribbean Sea via the Yucatan Channel between Mexico and Cuba, with the narrow connection to the Atlantic, the Gulf experiences very small tidal ranges. The size of the Gulf basin is approximately 1.6 million km2, almost half of the basin is shallow continental shelf waters. The basin contains a volume of roughly 2,500 quadrillion liters, the consensus among geologists who have studied the geology of the Gulf of Mexico, is that prior to the Late Triassic, the Gulf of Mexico did not exist. It was created by the collision of plates that formed Pangea. As interpreted by Roy Van Arsdale and Randel T. Cox, geologists and other Earth scientists agree in general that the present Gulf of Mexico basin originated in Late Triassic time as the result of rifting within Pangea. The rifting was associated with zones of weakness within Pangea, including sutures where the Laurentia, South American, first, there was a Late Triassic-Early Jurassic phase of rifting during which rift valleys formed and filled with continental red beds. Second, as rifting progressed through Early and Middle Jurassic time and it was at this time that tectonics first created a connection to the Pacific Ocean across central Mexico and later eastward to the Atlantic Ocean. This flooded the basin created by rifting and crustal thinning to create the Gulf of Mexico. While the Gulf of Mexico was a basin, the subsiding transitional crust was blanketed by the widespread deposition of Louann Salt. Initially, during the Late Jurassic, continued rifting widened the Gulf of Mexico and progressed to the point that sea-floor spreading, at this point, sufficient circulation with the Atlantic Ocean was established that the deposition of Louann Salt ceased. During the Late Jurassic through Early Cretaceous, the occupied by the Gulf of Mexico experienced a period of cooling. The subsidence was the result of a combination of stretching, cooling. Initially, the combination of stretching and cooling caused about 5–7 km of tectonic subsidence of the central thin transitional
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Arctic Ocean
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The Arctic Ocean is the smallest and shallowest of the worlds five major oceans. Alternatively, the Arctic Ocean can be seen as the northernmost part of the all-encompassing World Ocean, located mostly in the Arctic north polar region in the middle of the Northern Hemisphere, the Arctic Ocean is almost completely surrounded by Eurasia and North America. It is partly covered by sea ice throughout the year and almost completely in winter, the summer shrinking of the ice has been quoted at 50%. The US National Snow and Ice Data Center uses satellite data to provide a record of Arctic sea ice cover. The Arctic may become ice free for the first time in human history within a few years or by 2040, for much of European history, the north polar regions remained largely unexplored and their geography conjectural. He was probably describing loose sea ice known today as growlers or bergy bits, his Thule was probably Norway, early cartographers were unsure whether to draw the region around the North Pole as land or water. The makers of navigational charts, more conservative than some of the more fanciful cartographers, tended to leave the region blank and this lack of knowledge of what lay north of the shifting barrier of ice gave rise to a number of conjectures. In England and other European nations, the myth of an Open Polar Sea was persistent, john Barrow, longtime Second Secretary of the British Admiralty, promoted exploration of the region from 1818 to 1845 in search of this. In the United States in the 1850s and 1860s, the explorers Elisha Kane, even quite late in the century, the eminent authority Matthew Fontaine Maury included a description of the Open Polar Sea in his textbook The Physical Geography of the Sea. Nevertheless, as all the explorers who travelled closer and closer to the reported, the polar ice cap is quite thick. Fridtjof Nansen was the first to make a crossing of the Arctic Ocean. The first surface crossing of the ocean was led by Wally Herbert in 1969, in a dog sled expedition from Alaska to Svalbard, with air support. The first nautical transit of the pole was made in 1958 by the submarine USS Nautilus. Since 1937, Soviet and Russian manned drifting ice stations have extensively monitored the Arctic Ocean, scientific settlements were established on the drift ice and carried thousands of kilometres by ice floes. In World War II, the European region of the Arctic Ocean was heavily contested, the Arctic Ocean occupies a roughly circular basin and covers an area of about 14,056,000 km2, almost the size of Antarctica. The coastline is 45,390 km long and it is surrounded by the land masses of Eurasia, North America, Greenland, and by several islands. It is connected to the Pacific Ocean by the Bering Strait and to the Atlantic Ocean through the Greenland Sea, countries bordering the Arctic Ocean are, Russia, Norway, Iceland, Greenland, Canada and the United States. There are several ports and harbours around the Arctic Ocean In Alaska, in Canada, ships may anchor at Churchill in Manitoba, Nanisivik in Nunavut, Tuktoyaktuk or Inuvik in the Northwest territories
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Mid-Atlantic Ridge
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In the North Atlantic, it separates the Eurasian and North American Plates, whereas in the South Atlantic it separates the African and South American Plates. The ridge extends from a junction with the Gakkel Ridge northeast of Greenland southward to the Bouvet Triple Junction in the South Atlantic, although the Mid-Atlantic Ridge is mostly an underwater feature, portions of it have enough elevation to extend above sea level. The section of the ridge that includes the island of Iceland is also known as the Reykjanes Ridge, the ridge has an average spreading rate of about 2.5 cm per year. A ridge under the Atlantic Ocean was first inferred by Matthew Fontaine Maury in 1850, the ridge was discovered during the expedition of HMS Challenger in 1872. A team of scientists on board, led by Charles Wyville Thomson, the existence of such a ridge was confirmed by sonar in 1925 and was found to extend around the Cape of Good Hope into the Indian Ocean by the German Meteor expedition. Ewing, Heezen and Tharp discovered that the ridge is part of a 40, the ridge is central to the breakup of the hypothetical supercontinent of Pangaea that began some 180 million years ago. The Mid-Atlantic Ridge includes a deep valley that runs along the axis of the ridge along nearly its entire length. This rift marks the boundary between adjacent tectonic plates, where magma from the mantle reaches the seafloor, erupting as lava. This trench, however, is not regarded as the boundary between the North and South American Plates, nor the Eurasian and African Plates and this bulge is thought to be caused by upward convective forces in the asthenosphere pushing the oceanic crust and lithosphere. This divergent boundary first formed in the Triassic period, when a series of three-armed grabens coalesced on the supercontinent Pangaea to form the ridge, usually, only two arms of any given three-armed graben become part of a divergent plate boundary. The failed arms are called aulacogens, and the aulacogens of the Mid-Atlantic Ridge eventually became many of the river valleys seen along the Americas. The Fundy Basin on the Atlantic coast of North America between New Brunswick and Nova Scotia in Canada is evidence of the ancestral Mid-Atlantic Ridge, atlantis Massif Central Atlantic Magmatic Province Fifteen-Twenty Fracture Zone Evans, Rachel. Plumbing Depths to Reach New Heights, Marie Tharp Explains Marine Geological Maps, the Library of Congress Information Bulletin. MAR-ECO, a Census of Marine Life project on life along the Mid-Atlantic Ridge
39.
Mantle (geology)
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The mantle is a layer inside a terrestrial planet and some other rocky planetary bodies. For a mantle to form, the body must be large enough to have undergone the process of planetary differentiation by density. The mantle surrounds the planetary core, the mantle is surrounded by the crust. The terrestrial planets, the Moon, two of Jupiters moons and the asteroid Vesta each have a made of silicate rock. Interpretation of spacecraft data suggests that at least two moons of Jupiter, as well as Titan and Triton each have a mantle made of ice or other solid volatile substances. The interior of Earth, similar to the terrestrial planets, is divided into layers of different composition. The mantle is a layer between the crust and the outer core, Earths mantle is a silicate rocky shell with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earths volume and it is predominantly solid but in geological time it behaves as a very viscous fluid. The mantle encloses the hot core rich in iron and nickel, past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface. A thin crust, the part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. In some places under the ocean the mantle is exposed on the surface of Earth. The mantle is divided into sections which are based upon results from seismology and these layers are the following, the upper mantle, the transition zone, the lower mantle, and anomalous core–mantle boundary with a variable thickness. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, below the lithosphere the upper mantle becomes notably more plastic. In some regions below the lithosphere, the shear velocity is reduced. Inge Lehmann discovered a seismic discontinuity at about 220 km depth, although this discontinuity has been found in other studies, the transition zone is an area of great complexity, it physically separates the upper and lower mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous, the D layer at the core–mantle boundary separates the mantle from the core. A principal source of the heat that drives plate tectonics is the decay of uranium, thorium. The mantle differs substantially from the crust in its properties as the direct consequence of the difference in composition
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Crust (geology)
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In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crust of the Earth is composed of a variety of igneous, metamorphic. The crust is underlain by the mantle, the upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity, the crust occupies less than 1% of Earths volume. The crust of the Earth is of two types, oceanic and continental. The oceanic crust is 5 km to 10 km thick and is composed primarily of basalt, diabase, the continental crust is typically from 30 km to 50 km thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust, both the continental and oceanic crust float on the mantle. Because the continental crust is thicker, it both to greater elevations and greater depth than the oceanic crust. The slightly lower density of continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, the temperature of the crust increases with depth, reaching values typically in the range from about 200 °C to 400 °C at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere, because of convection in the underlying plastic upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C for every kilometer locally in the part of the crust. Earth has probably always had some form of basaltic crust, in contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4, some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane. The average age of the current Earths continental crust has been estimated to be about 2.0 billion years, most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth, formation of new continental crust is linked to periods of intense orogeny, these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The continental crust has a composition similar to that of andesite. The most abundant minerals in Earths continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle
41.
Geomagnetic reversal
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The time spans of chrons are randomly distributed with most being between 0.1 and 1 million years with an average of 450,000 years. Most reversals are estimated to take between 1,000 and 10,000 years, the latest one, the Brunhes–Matuyama reversal, occurred 780,000 years ago, and may have happened very quickly, within a human lifetime. A brief complete reversal, known as the Laschamp event, occurred only 41,000 years ago during the last glacial period and that reversal lasted only about 440 years with the actual change of polarity lasting around 250 years. During this change the strength of the magnetic field weakened to 5% of its present strength, brief disruptions that do not result in reversal are called geomagnetic excursions. In the early 20th century, geologists first noticed that some rocks were magnetized opposite to the direction of the local Earths field. The first estimate of the timing of magnetic reversals was made by Motonori Matuyama in the 1920s, at the time, the Earths polarity was poorly understood, and the possibility of reversal aroused little interest. Three decades later, when Earths magnetic field was better understood, most paleomagnetic research in the late 1950s included an examination of the wandering of the poles and continental drift. In the absence of reliable methods for obtaining absolute ages for rocks, the next major advance in understanding reversals came when techniques for radiometric dating were developed in the 1950s. They produced the first magnetic-polarity time scale in 1959, as they accumulated data, they continued to refine this scale in competition with Don Tarling and Ian McDougall at the Australian National University. A group led by Neil Opdyke at the Lamont-Doherty Geological Observatory showed that the pattern of reversals was recorded in sediments from deep-sea cores. During the 1950s and 1960s information about variations in the Earths magnetic field was gathered largely by means of research vessels, but the complex routes of ocean cruises rendered the association of navigational data with magnetometer readings difficult. Only when data were plotted on a map did it become apparent that remarkably regular, thus, sea floor spreading from a central ridge will produce pairs of magnetic stripes parallel to the ridge. The Morley–Vine–Matthews hypothesis was the first key scientific test of the spreading theory of continental drift. The same magnetic anomalies were found over most of the worlds oceans, past field reversals can be and have been recorded in the frozen ferromagnetic minerals of consolidated sedimentary deposits or cooled volcanic flows on land. The past record of geomagnetic reversals was first noticed by observing the magnetic anomalies on the ocean floor. Because no existing unsubducted sea floor is more than about 180 million years old, most sedimentary rocks incorporate tiny amounts of iron rich minerals, whose orientation is influenced by the ambient magnetic field at the time at which they formed. These rocks can preserve a record of the if it is not later erased by chemical, physical or biological change. Because the magnetic field is global, similar patterns of magnetic variations at different sites may be used to age in different locations
42.
Convergent boundary
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As a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent boundaries. When two plates move towards one another, they form either a subduction zone or a continental collision and this depends on the nature of the plates involved. In a subduction zone, the plate, which is normally a plate with oceanic crust, moves beneath the other plate. During collisions between two plates, large mountain ranges, such as the Himalayas are formed. The nature of a convergent boundary depends on the type of plates that are colliding, at an oceanic-continental convergent boundary, the oceanic lithosphere will always subduct below the continental lithosphere. This is caused by the density difference between the oceanic and continental lithosphere. This type of boundary is called a subduction zone. At the surface, the expression is commonly an oceanic trench which forms on the oceanic side. On the continental side, a chain of volcanoes forms above the location of the subducting plate, an example of a continental-oceanic subduction zone is the area along the western coast of South America where the oceanic Nazca Plate is being subducted beneath the continental South American Plate. A volcanic arc is formed on the plate, above the location of the downgoing oceanic slab. The volcanic arc is the expression of the magma that is generated by hydrous melting of the mantle above the downgoing slab. The buoyant fluids then rise into the asthenosphere, where they lower the temperature of the mantle. Either action will create extensive mountain ranges and it may have also pushed nearby parts of the Asian continent aside to the east. When two plates with oceanic crust converge, they create an island arc as one plate is subducted below the other. The arc is formed from volcanoes which erupt through the plate as the descending plate melts below it. The arc shape occurs because of the surface of the earth. A deep oceanic trench is located in front of such arcs where the descending slab dips downward, plates may collide at an oblique angle rather than head-on to each other, and this may cause strike-slip faulting along the collision zone, in addition to subduction or compression. Not all plate boundaries are easily defined, some are broad belts whose movements are unclear to scientists
43.
Heaviside step function
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The Heaviside step function, or the unit step function, usually denoted by H or θ, is a discontinuous function whose value is zero for negative argument and one for positive argument. It is an example of the class of step functions. Oliver Heaviside, who developed the operational calculus as a tool in the analysis of telegraphic communications, represented the function as 1. This is sometimes written as H, = ∫ − ∞ x δ d s although this expansion may not hold for x =0, in this context, the Heaviside function is the cumulative distribution function of a random variable which is almost surely 0. In operational calculus, useful answers seldom depend on which value is used for H, however, the choice may have some important consequences in functional analysis and game theory, where more general forms of continuity are considered. Some common choices can be seen below, unlike the usual case, the definition of H is significant. The discrete-time unit impulse is the first difference of the discrete-time step δ = H − H and this function is the cumulative summation of the Kronecker delta, H = ∑ k = − ∞ n δ where δ = δ k,0 is the discrete unit impulse function. If we take H = 1/2, equality holds in the limit, there are many other smooth, analytic approximations to the step function. Among the possibilities are, H = lim k → ∞ H = lim k → ∞ These limits hold pointwise, in general, however, pointwise convergence need not imply distributional convergence, and vice versa distributional convergence need not imply pointwise convergence. For example, all three of the approximations are cumulative distribution functions of common probability distributions, The logistic, Cauchy and normal distributions. Since H is usually used in integration, and the value of a function at a point does not affect its integral. Indeed when H is considered as a distribution or an element of L∞ it does not even make sense to talk of a value at zero, if using some analytic approximation then often whatever happens to be the relevant limit at zero is used. There exist various reasons for choosing a particular value, H = 1/2 is often used since the graph then has rotational symmetry, put another way, H − 1/2 is then an odd function. In this case the relation with the sign function holds for all x, H =12 +12 sgn . H =1 is used when H needs to be right-continuous, for instance cumulative distribution functions are usually taken to be right continuous, as are functions integrated against in Lebesgue–Stieltjes integration. In this case H is the function of a closed semi-infinite interval. The corresponding probability distribution is the degenerate distribution, H =0 is used when H needs to be left-continuous. In this case H is a function of an open semi-infinite interval
44.
Heat equation
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The heat equation is a parabolic partial differential equation that describes the distribution of heat in a given region over time. In the physical problem of variation, u is the temperature. For the mathematical treatment it is sufficient to consider the case α =1, note that the state equation, given by the first law of thermodynamics, is written in the following form. This form is general and particularly useful to recognize which property influences which term. ρ c p ∂ T ∂ t − ∇ ⋅ = q ˙ V where q ˙ V is the heat flux. The heat equation is of importance in diverse scientific fields. In mathematics, it is the prototypical parabolic partial differential equation, in probability theory, the heat equation is connected with the study of Brownian motion via the Fokker–Planck equation. In financial mathematics it is used to solve the Black–Scholes partial differential equation, the diffusion equation, a more general version of the heat equation, arises in connection with the study of chemical diffusion and other related processes. Suppose one has a function u that describes the temperature at a given location and this function will change over time as heat spreads throughout space. The heat equation is used to determine the change in the function u over time, the rate of change of u is proportional to the curvature of u. Thus, the sharper the corner, the faster it is rounded off. Over time, the tendency is for peaks to be eroded, if u is linear in space at a given point, then u has reached steady-state and is unchanging at this point. The image to the right is animated and describes the way changes in time along a metal bar. This is essentially saying that temperature comes either from some source or from earlier in time because heat permeates but is not created from nothingness and this is a property of parabolic partial differential equations and is not difficult to prove mathematically. Another interesting property is that if u has a discontinuity at an initial time t = t0. The heat equation is used in probability and describes random walks and it is also applied in financial mathematics for this reason. The heat equation is derived from Fouriers law and conservation of energy and that is, Δ Q = c p ρ Δ u where cp is the specific heat capacity and ρ is the mass density of the material. Choosing zero energy at zero temperature, this can be rewritten as Q = c p ρ u. If no work is done and there are neither heat sources nor sinks, by conservation of energy, ∫ t − Δ t t + Δ t ∫ x − Δ x x + Δ x d ξ d τ =0
45.
Error function
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In mathematics, the error function is a special function of sigmoid shape that occurs in probability, statistics, and partial differential equations describing diffusion. It is defined as, erf =1 π ∫ − x x e − t 2 d t =2 π ∫0 x e − t 2 d t. The error function is used in measurement theory, and its use in branches of mathematics is typically unrelated to the characterization of measurement errors. In statistics, it is common to have a variable Y, the error is then defined as ε = Y ^ − Y. This makes the error a normally distributed random variable with mean 0 and some variance σ2 and this is true for any random variable with distribution N, but the application to error variables is how the error function got its name. The previous paragraph can be generalized to any variance, given a variable ε ∼ N and this is used in statistics to predict behavior of any sample with respect to the population mean. This usage is similar to the Q-function, which in fact can be written in terms of the error function, another form of erfc for non-negative x is known as Craigs formula, erfc =2 π ∫0 π /2 exp d θ. The imaginary error function, denoted erfi, is defined as erfi = − i erf =2 π ∫0 x e t 2 d t =2 π e x 2 D, where D is the Dawson function. Despite the name imaginary error function, erfi is real when x is real, the error function is related to the cumulative distribution Φ, the integral of the standard normal distribution, by Φ =12 +12 erf =12 erfc . The property erf = − erf means that the function is an odd function. This directly results from the fact that the integrand e − t 2 is an even function, for any complex number z, erf = erf ¯ where z ¯ is the complex conjugate of z. The integrand ƒ = exp and ƒ = erf are shown in the complex z-plane in figures 2 and 3, level of Im =0 is shown with a thick green line. Negative integer values of Im are shown with red lines. Positive integer values of Im are shown with blue lines. Intermediate levels of Im = constant are shown with thin green lines, intermediate levels of Re = constant are shown with thin red lines for negative values and with thin blue lines for positive values. The error function at +∞ is exactly 1, at the real axis, erf approaches unity at z → +∞ and −1 at z → −∞. At the imaginary axis, it tends to ±i∞, the error function is an entire function, it has no singularities and its Taylor expansion always converges. =2 π which holds for complex number z
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