1.
Granite
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Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be white, pink, or gray in color. The word granite comes from the Latin granum, a grain, in reference to the structure of such a holocrystalline rock. By definition, granite is a rock with at least 20% quartz. The term granitic means granite-like and is applied to granite and a group of igneous rocks with similar textures and slight variations in composition. Occasionally some individual crystals are larger than the groundmass, in case the texture is known as porphyritic. A granitic rock with a texture is known as a granite porphyry. Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks, petrographic examination is required for identification of specific types of granitoids. The extrusive igneous rock equivalent of granite is rhyolite, Granite is nearly always massive, hard and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 •1019 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C, it is reduced in the presence of water. Granite has poor primary permeability, but strong secondary permeability, true granite according to modern petrologic convention contains both plagioclase and alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite, when a granitoid contains less than 10% orthoclase, it is called tonalite, pyroxene and amphibole are common in tonalite. A granite containing both muscovite and biotite micas is called a binary or two-mica granite, two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites. A worldwide average of the composition of granite, by weight percent, based on 2485 analyses. Much of it was intruded during the Precambrian age, it is the most abundant basement rock that underlies the relatively thin veneer of the continents. Outcrops of granite tend to form tors and rounded massifs, granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite often occurs as small, less than 100 km² stock masses
2.
Russian language
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Russian is an East Slavic language and an official language in Russia, Belarus, Kazakhstan, Kyrgyzstan and many minor or unrecognised territories. Russian belongs to the family of Indo-European languages and is one of the four living members of the East Slavic languages, written examples of Old East Slavonic are attested from the 10th century and beyond. It is the most geographically widespread language of Eurasia and the most widely spoken of the Slavic languages and it is also the largest native language in Europe, with 144 million native speakers in Russia, Ukraine and Belarus. Russian is the eighth most spoken language in the world by number of native speakers, the language is one of the six official languages of the United Nations. Russian is also the second most widespread language on the Internet after English, Russian distinguishes between consonant phonemes with palatal secondary articulation and those without, the so-called soft and hard sounds. This distinction is found between pairs of almost all consonants and is one of the most distinguishing features of the language, another important aspect is the reduction of unstressed vowels. Russian is a Slavic language of the Indo-European family and it is a lineal descendant of the language used in Kievan Rus. From the point of view of the language, its closest relatives are Ukrainian, Belarusian, and Rusyn. An East Slavic Old Novgorod dialect, although vanished during the 15th or 16th century, is considered to have played a significant role in the formation of modern Russian. In the 19th century, the language was often called Great Russian to distinguish it from Belarusian, then called White Russian and Ukrainian, however, the East Slavic forms have tended to be used exclusively in the various dialects that are experiencing a rapid decline. In some cases, both the East Slavic and the Church Slavonic forms are in use, with different meanings. For details, see Russian phonology and History of the Russian language and it is also regarded by the United States Intelligence Community as a hard target language, due to both its difficulty to master for English speakers and its critical role in American world policy. The standard form of Russian is generally regarded as the modern Russian literary language, mikhail Lomonosov first compiled a normalizing grammar book in 1755, in 1783 the Russian Academys first explanatory Russian dictionary appeared. By the mid-20th century, such dialects were forced out with the introduction of the education system that was established by the Soviet government. Despite the formalization of Standard Russian, some nonstandard dialectal features are observed in colloquial speech. Thus, the Russian language is the 6th largest in the world by number of speakers, after English, Mandarin, Hindi/Urdu, Spanish, Russian is one of the six official languages of the United Nations. Education in Russian is still a choice for both Russian as a second language and native speakers in Russia as well as many of the former Soviet republics. Russian is still seen as an important language for children to learn in most of the former Soviet republics, samuel P. Huntington wrote in the Clash of Civilizations, During the heyday of the Soviet Union, Russian was the lingua franca from Prague to Hanoi
3.
Supercontinent
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In geology, a supercontinent is the assembly of most or all of Earths continental blocks or cratons to form a single large landmass. However, the definition of a supercontinent can be ambiguous, Many earth scientists, such as P. F. Hoffman, use the term supercontinent to mean a clustering of all continents. This definition leaves room for interpretation when labeling a continental body and is easier to apply to Precambrian times, the landmass of Pangaea is the collective name describing all of these continental masses when they were most recently in proximity to one another. This would classify Pangaea as a supercontinent, according to the definition by Rogers and Santosh, a supercontinent does not exist today. Supercontinents have assembled and dispersed multiple times in the geologic past, the positions of continents have been accurately determined back to the early Jurassic. However, beyond 200 Ma, continental positions are less certain. The following table displays historical supercontinents, using a general definition, there are two contrasting models for supercontinent evolution through geological time. The first model theorizes that at least two separate supercontinents existed comprising Vaalbara and Kenorland, the Neoarchean supercontinent consisted of Superia and Sclavia. These parts of Neoarchean age broke off at ~2300 and 2090 Ma, Nuna continued to develop during the Mesoproterozoic, primarily by lateral accretion of juvenile arcs, and in ~1000 Ma Nuna collided with other land masses, forming Rodinia. Between ~800 and 700 Ma Rodinia broke apart, however, before completely breaking up, some fragments of Rodinia had already come together to form Gondwana by ~530 Ma. Pangaea formed by ~300 Ma through the collision of Gondwana, Laurentia, Baltica, during the intervening periods, the poles conform to a unified apparent polar wander path. The explanation for the duration of the Protopangea-Paleopangea supercontinent appears to be that Lid Tectonics prevailed during Precambrian times. Plate Tectonics as seen on the contemporary Earth became dominant only during the part of geological times. The Phanerozoic supercontinent Pangaea began to break up 180 Ma and is doing so today. Because Pangaea is the most recent of Earths supercontinents, it is the most well known, contributing to Pangaeas popularity in the classroom is the fact that its reconstruction is almost as simple as fitting the present continents bordering the Atlantic-type oceans like puzzle pieces. A supercontinent cycle is the break-up of one supercontinent and the development of another, supercontinent cycles are not the same as the Wilson cycle, which is the opening and closing of an individual oceanic basin. The Wilson cycle rarely synchronizes with the timing of a supercontinent cycle, however, supercontinent cycles and Wilson cycles were both involved in the creation of Pangaea and Rodinia
4.
Precambrian
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The Precambrian is the earliest period of Earths history, set before the current Phanerozoic Eon. The Precambrian is a supereon that is subdivided into three eons of the time scale. It spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 541 million years ago, the Precambrian accounts for 89% of geologic time. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earths history, the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from that time are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion. A stable crust was apparently in place by 4,412 Ma, the term Precambrian is recognized by the International Commission on Stratigraphy as a general term including the Archean and Proterozoic eons. It is still used by geologists and paleontologists for general discussions not requiring the more specific eon names and it was briefly called the Cryptozoic eon. A specific date for the origin of life has not been determined, carbon found in 3.8 billion year old rocks from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have found in Western Australia. Probable fossils 100 million years older have been found in the same area, there is a fairly solid record of bacterial life throughout the remainder of the Precambrian. The oldest fossil evidence from that era of such complex life comes from the Lantian formation of the Ediacarian period, a very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota, hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic era. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale. The explosion in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life, while land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic mats that covered terrestrial areas. Evidence of the details of plate motions and other activity in the Precambrian has been poorly preserved. It is generally believed that small proto-continents existed prior to 4280 Ma, the supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, one of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a Snowball Earth. The atmosphere of the early Earth is not well understood, most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and was lacking in free oxygen
5.
Plate reconstruction
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This article describes techniques, for a history of the movement of tectonic plates, see Geological history of Earth. This helps determine the shape and make-up of ancient supercontinents and provides a basis for paleogeographic reconstructions, an important part of reconstructing past plate configurations is to define the edges of areas of the lithosphere that have acted independently at some time in the past. Most present plate boundaries are easily identifiable from the pattern of recent seismicity and this is now backed up by the use of GPS data, to confirm the presence of significant relative movement between plates. Identifying past plate boundaries within current plates is based on evidence for an ocean that has now closed up. The line where the used to be is normally marked by pieces of the crust from that ocean, included in the collision zone. The line across which two plates became joined to form a larger plate, is known as a suture. In many orogenic belts, the collision is not just between two plates, but involves the sequential accretion of smaller terranes, terranes are smaller pieces of continental crust that have been caught up in an orogeny, such as continental fragments or island arcs. Plate motions, both those observable now and in the past, are referred ideally to a frame that allows other plate motions to be calculated. For example, a plate, such as the African plate. By composition of reconstructions, additional plates can be reconstructed to the central plate, a global hotspot reference frame has been postulated but there is now evidence that not all hotspots are necessarily fixed in their locations relative to one another or the earths spin axis. However, there are groups of such hotspots that appear to be fixed within the constraints of available data, the movement of a rigid body, such as a plate, on the surface of a sphere can be described as rotation about a fixed axis. This pole of rotation is known as an Euler pole, the movement of a plate is completely specified in terms of its Euler pole and the angular rate of rotation about the pole. Euler poles defined for current plate motions can be used to reconstruct plates in the recent past, at earlier stages of earths history, new Euler poles need to be defined. It was suggested recently that paleomagnetic Euler poles derived from apparent polar wander path could potentially extend the age limit of marine geophysical observations. In order to move backward in time it is necessary to provide information on either relative or absolute positions of the plates being reconstructed such that an Euler pole can be calculated. These are quantitative methods of reconstruction, certain fits between continents, particularly that between South America and Africa, were known long before the development of a theory that could adequately explain them. Plate reconstructions in the recent geological past mainly use the pattern of stripes in oceanic crust to remove the effects of seafloor spreading. The individual stripes are dated from magnetostratigraphy so that their time of formation is known, each stripe represents a plate boundary at a particular time in the past, allowing the two plates to be repositioned relative to one another
6.
Gigaannus
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A year is the orbital period of the Earth moving in its orbit around the Sun. Due to the Earths axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the globe, four seasons are recognized, spring, summer, autumn. In tropical and subtropical regions several geographical sectors do not present defined seasons, but in the seasonal tropics, a calendar year is an approximation of the number of days of the Earths orbital period as counted in a given calendar. The Gregorian, or modern, calendar, presents its calendar year to be either a common year of 365 days or a year of 366 days, as do the Julian calendars. For the Gregorian calendar the average length of the year across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol a to represent a year of either 365 or 366 days, in English, the abbreviations y and yr are commonly used. In astronomy, the Julian year is a unit of time, it is defined as 365.25 days of exactly 86400 seconds, totalling exactly 31557600 seconds in the Julian astronomical year. The word year is used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year. Similarly, year can mean the period of any planet, for example. The term can also be used in reference to any long period or cycle, west Saxon ġēar, Anglian ġēr continues Proto-Germanic *jǣran. Cognates are German Jahr, Old High German jār, Old Norse ár and Gothic jer, all the descendants of the Proto-Indo-European noun *yeh₁rom year, season. Cognates also descended from the same Proto-Indo-European noun are Avestan yārǝ year, Greek ὥρα year, season, period of time, Old Church Slavonic jarŭ, Latin annus is from a PIE noun *h₂et-no-, which also yielded Gothic aþn year. Both *yeh₁-ro- and *h₂et-no- are based on verbal roots expressing movement, *h₁ey- and *h₂et- respectively, the Greek word for year, ἔτος, is cognate with Latin vetus old, from the PIE word *wetos- year, also preserved in this meaning in Sanskrit vat-sa- yearling and vat-sa-ras year. Derived from Latin annus are a number of English words, such as annual, annuity, anniversary, etc. per annum means each year, anno Domini means in the year of the Lord. No astronomical year has an number of days or lunar months. Financial and scientific calculations often use a 365-day calendar to simplify daily rates, in the Julian calendar, the average length of a year is 365.25 days. In a non-leap year, there are 365 days, in a year there are 366 days
7.
Pannotia
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Pannotia formed when Laurentia was located adjacent to the two major South American cratons, Amazonia and Río de la Plata. The opening of the Iapetus Ocean separated Laurentia from Baltica, Amazonia, piper 1976 was probably the first to propose a Proterozoic supercontinent preceding Pangaea, today known as Rodinia. The reconstruction of Bond et al. is virtually identical to that of Dalziel 1997, another term for the supercontinent that is thought to have existed at the end of Neoproterozoic time is Greater Gondwanaland, suggested by Stern 1994. This term recognizes that the supercontinent of Gondwana, which formed at the end of the Neoproterozoic, was part of the much larger end-Neoproterozoic supercontinent. Powell, however, objected to this renaming and instead proposed Stumps term for the latter supercontinent, the formation of Pannotia began during the Pan-African orogeny when the Congo continent got caught between the northern and southern halves of the previous supercontinent Rodinia some 750 Ma. The peak in this mountain building event was around 640–610 Ma, the formation of Pannotia was the result of Rodinia turning itself inside out. When Pannotia had formed Africa was located at the centre surrounded by the rest of Gondwana, South America, Arabia, Madagascar, India, Antarctica, Laurentia, who escaped out of Rodinia, Baltica, and Siberia kept the relative positions they had in Rodinia. The Cathaysian and Cimmerian terranes were located along the margins of east Gondwana. The Avalonian-Cadomian terranes were located along the northern margins of western Gondwana. This orogeny probably extended north into the Uralian margin of Baltica, Pannotia formed by subduction of exterior oceans over a geoid low, whereas Pangaea formed by subduction of interior oceans over a geoid high perhaps caused by superplumes and slab avalanche events. One of the major of these orogenies was the collision between East and West Gondwana or the East African Orogeny, 600-500 Ma two Brazilian interior orogenies got highly deformed and metamorphosed between a series of colliding cratons, Amazonia, West Africa-São Luís, and São Francisco-Congo-Kasai. The material that was accreted included 950-850 Ma mafic meta-igneous complexes, the break-up of Pannotia was accompanied by sea level rise, dramatic changes in climate and ocean water chemistry, and rapid metazoan diversification. Bond, Nickeson & Kominz 1984 found Neoproterozoic passive margin sequences worldwide — the first indication of a Late Neoproterozoic supercontinent, the Iapetus Ocean started to open while Pannotia was being assembled,200 m. y. after the break-up of Rodinia. Plate tectonics Supercontinent cycle Pan-African orogeny An image showing Pannotia according to Christopher Scotese, stampfli, G. M. von Raumer, J. F. Borel, G. D. Paleozoic evolution of pre-Variscan terranes, from Gondwana to the Variscan collision
8.
Geodynamics
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Geodynamics is a subfield of geophysics dealing with dynamics of the Earth. It also attempts to probe the internal activity by measuring magnetic fields, gravity, methods of geodynamics are also applied to exploration of other planets. Geodynamics is generally concerned with processes that move throughout the Earth. In the Earth’s interior, movement happens when rocks melt or deform and this deformation may be brittle, elastic, or plastic, depending on the magnitude of the stress and the material’s physical properties, especially the stress relaxation time scale. Rocks are structurally and compositionally heterogeneous and are subjected to variable stresses, when working with geological timescales and lengths, it is convenient to use the continuous medium approximation and equilibrium stress fields to consider the average response to average stress. Experts in geodynamics commonly use data from geodetic GPS, InSAR, rocks and other geological materials experience strain according three distinct modes, elastic, plastic, and brittle depending on the properties of the material and the magnitude of the stress field. Stress is defined as the force per unit area exerted on each part of the rock. Pressure is the part of stress changes the volume of a solid. If there is no shear, the fluid is in hydrostatic equilibrium, since, over long periods, rocks readily deform under pressure, the Earth is in hydrostatic equilibrium to a good approximation. The pressure on rock depends only on the weight of the rock above, and this depends on gravity, in a body like the Moon, the density is almost constant, so a pressure profile is readily calculated. In the Earth, the compression of rocks with depth is significant, elastic deformation is always reversible, which means that if the stress field associated with elastic deformation is removed, the material will return to its previous state. Materials only behave elastically when the arrangement along the axis being considered of material components remains unchanged. This means that the magnitude of the stress cannot exceed the strength of a material. If stress exceeds the strength of a material, bonds begin to break. During ductile deformation, this process of atomic rearrangement redistributes stress, examples include bending of the lithosphere under volcanic islands or sedimentary basins, and bending at oceanic trenches. Ductile deformation happens when transport processes such as diffusion and advection that rely on chemical bonds to be broken, when strain localizes faster than these relaxation processes can redistribute it, brittle deformation occurs. In other words, any fracture, however small, tends to focus strain at its leading edge, in general, the mode of deformation is controlled not only by the amount of stress, but also by the distribution of strain and strain associated features. Structural geologists study the results of deformation, using observations of rock, especially the mode, structural geology is an important complement to geodynamics because it provides the most direct source of data about the movements of the Earth
9.
Paleomagnetism
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This term is also sometimes used for natural remanent magnetization. Paleomagnetism is the study of the record of the Earths magnetic field in rocks, sediment, certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earths magnetic field, the record of geomagnetic reversals preserved in volcanic and sedimentary rock sequences provides a time-scale that is used as a geochronologic tool. Geophysicists who specialize in paleomagnetism are called paleomagnetists, paleomagnetists led the revival of the continental drift hypothesis and its transformation into plate tectonics. Apparent polar wander paths provided the first clear evidence for continental drift. Paleomagnetism continues to extend the history of plate tectonics back in time and are applied to the movement of continental fragments, paleomagnetism relied heavily on new developments in rock magnetism, which in turn has provided the foundation for new applications of magnetism. These include biomagnetism, magnetic fabrics, and environmental magnetism, as early as the 18th century, it was noticed that compass needles deviated near strongly magnetized outcrops. In 1797, Von Humboldt attributed this magnetization to lightning strikes, in the 19th century studies of the direction of magnetization in rocks showed that some recent lavas were magnetized parallel to the Earths magnetic field. Early in the 20th century, work by David, Brunhes, japanese geophysicist Motonori Matuyama showed that the Earths magnetic field reversed in the mid-Quaternary, a reversal now known as the Brunhes-Matuyama reversal. Blackett provided an impetus to paleomagnetism by inventing a sensitive astatic magnetometer in 1956. Alfred Wegener first proposed in 1915 that continents had once been joined together and had moved apart. Keith Runcorn and Edward A. Irving constructed apparent polar wander paths for Europe and these curves diverged, but could be reconciled if it was assumed that the continents had been in contact up to 200 million years ago. This provided the first clear evidence for continental drift. Then in 1963, Morley, Vine and Matthews showed that marine magnetic anomalies provided evidence for seafloor spreading, paleomagnetism is studied on a number of scales, Secular variation studies look at small-scale changes in the direction and intensity of the Earths magnetic field. The magnetic north pole is constantly shifting relative to the axis of rotation of the Earth, magnetism is a vector and so magnetic field variation is made up of palaeodirectional measurements of magnetic declination and magnetic inclination and palaeointensity measurements. Magnetostratigraphy uses the polarity reversal history of the Earths magnetic field recorded in rocks to determine the age of those rocks, reversals have occurred at irregular intervals throughout Earth history. The age and pattern of reversals is known from the study of sea floor spreading zones. The study of paleomagnetism is possible because iron-bearing minerals such as magnetite may record past directions of the Earths magnetic field, magnetic signatures in rocks can be recorded by several different mechanisms
10.
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
11.
Snowball Earth
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The Snowball Earth hypothesis proposes that Earths surface became entirely or nearly entirely frozen at least once, sometime earlier than 650 Mya. A number of unanswered questions remain, including whether the Earth was a full snowball, the snowball Earth episodes occurred before the sudden radiation of multicellular bioforms, known as the Cambrian explosion. The most recent snowball episode may have triggered the evolution of multicellularity, in the 1960s, Mikhail Budyko, a Russian climatologist, developed a simple energy-balance climate model to investigate the effect of ice cover on global climate. While Budykos model showed that this ice-albedo stability could happen, he concluded that it had in fact never happened, in 1971, Aron Faegre, an American physicist, showed that a similar energy-balance model predicted three stable global climates, one of which was snowball earth. This model introduced Edward Norton Lorenzs concept of intransitivity indicating that there could be a jump from one climate to another. The term snowball Earth was coined by Joseph Kirschvink in a paper published in 1992 within a lengthy volume concerning the biology of the Proterozoic eon. Franklyn Van Houtens discovery of a consistent geological pattern in which lake levels rose, interest in the notion of a snowball Earth increased dramatically after Paul F. The snowball Earth hypothesis was originally devised to explain geological evidence for the apparent presence of glaciers at tropical latitudes, according to modelling, an ice-albedo feedback would result in glacial ice rapidly advancing to the equator once the glaciers spread to within 25° to 30° of the equator. Therefore, the presence of deposits within the tropics suggests global ice cover. Critical to an assessment of the validity of the theory, therefore, is an understanding of the reliability and significance of the evidence that led to the belief that ice ever reached the tropics. This evidence must prove two things, that a bed contains sedimentary structures that could have been created only by glacial activity and this last point is very difficult to prove. The best that can be done is to estimate the age of the rocks using radiometric methods, the first two points are often the source of contention on a case-to-case basis. Many glacial features can also be created by means. The snowball Earth hypothesis was first posited to explain what were considered to be glacial deposits near the equator. Since tectonic plates move slowly over time, ascertaining their position at a point in Earths long history is not easy. In addition to considerations of how the recognizable landmasses could have fit together, when sedimentary rocks form, magnetic minerals within them tend to align themselves with the Earths magnetic field. Through the precise measurement of this palaeomagnetism, it is possible to estimate the latitude where the matrix was formed. This palaeomagnetic location of glacial sediments has been taken to suggest that glaciers extended from land to sea level in tropical latitudes at the time the sediments were deposited
12.
Cryogenian
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The Cryogenian is a geologic period that lasted from 720 to 635 million years ago. It forms the geologic period of the Neoproterozoic Era, preceded by the Tonian Period. The Sturtian and Marinoan glaciations during the Cryogenian period, which are the greatest ice ages known to have occurred on Earth and these events are the subject of much scientific controversy. The main debate contests whether these glaciations covered the planet or if a band of open sea survived near the equator. The Cryogenian period was ratified in 1990 by the International Commission on Stratigraphy, in contrast to most other time periods, the beginning of the Cryogenian is not linked to a globally observable and documented event. Instead, the base of the period is defined by a fixed age, that was set at 850 million years, until 2015. This is problematic as estimates of rock ages are variable and are subject to laboratory error, for instance, the time scale of the Cambrian Period is not reckoned by rock younger than a given age, but by the appearance of the worldwide Treptichnus pedum diagnostic trace fossil assemblages. This means that rocks can be recognized as Cambrian when examined in the field, currently, there is no consensus on what global event is a suitable candidate to mark the start of the Cryogenian Period, but a global glaciation would be a likely candidate. The name of the geologic period refers to the very cold climate of the Cryogenian. Characteristic glacial deposits indicate that Earth suffered the most severe ice ages in its history during this period, according to Eyles and Young, Late Proterozoic glaciogenic deposits are known from all the continents. They provide evidence of the most widespread and long-ranging glaciation on Earth, several glacial periods are evident, interspersed with periods of relatively warm climate, with glaciers reaching sea level in low paleolatitudes. Glaciers extended and contracted in a series of pulses, possibly reaching as far as the equator. The Cryogenian is generally considered to be divisible into at least two major worldwide glaciations, the Sturtian glaciation persisted from 720 to 660 million years ago, and the Marinoan glaciation which ended approximately 635 Ma, at the end of the Cryogenian. Before the start of the Cryogenian, around 750 Ma, the cratons that made up the supercontinent Rodinia started to rift apart, the superocean Mirovia began to close while the superocean Panthalassa began to form. The cratons later assembled into another supercontinent called Pannotia, in the Ediacaran, Eyles and Young state, Most Neoproterozoic glacial deposits accumulated as glacially influenced marine strata along rifted continental margins or interiors. Worldwide deposition of dolomite might have reduced carbon dioxide. The break up along the margins of Laurentia at about 750 Ma occurs at about the time as the deposition of the Rapitan Group in North America. A similar period of rifting at about 650 Ma occurred with the deposition of the Ice Brook Formation in North America, the Sturtian and Marinoan are local divisions within the Adelaide Rift Complex
13.
Evolution
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Evolution is change in the heritable characteristics of biological populations over successive generations. Evolutionary processes give rise to biodiversity at every level of organisation, including the levels of species, individual organisms. In July 2016, scientists reported identifying a set of 355 genes from the LUCA of all living on Earth. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, existing patterns of biodiversity have been shaped both by speciation and by extinction. More than 99 percent of all species that lived on Earth are estimated to be extinct. Estimates of Earths current species range from 10 to 14 million, more recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. In the mid-19th century, Charles Darwin formulated the theory of evolution by natural selection. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are fitted for the functional roles they perform. The processes by which the changes occur, from one generation to another, are called evolutionary processes or mechanisms, the four most widely recognized evolutionary processes are natural selection, genetic drift, mutation and gene migration. Natural selection and genetic drift sort variation, mutation and gene migration create variation, consequences of selection can include meiotic drive, nonrandom mating and genetic hitchhiking. In the early 20th century the modern evolutionary synthesis integrated classical genetics with Darwins theory of evolution by natural selection through the discipline of population genetics, the importance of natural selection as a cause of evolution was accepted into other branches of biology. Moreover, previously held notions about evolution, such as orthogenesis, evolutionism, evolutionary computation, a sub-field of artificial intelligence, involves the application of Darwinian principles to problems in computer science. The proposal that one type of organism could descend from another type goes back to some of the first pre-Socratic Greek philosophers, such as Anaximander, such proposals survived into Roman times. The poet and philosopher Lucretius followed Empedocles in his masterwork De rerum natura, in contrast to these materialistic views, Aristotelianism considered all natural things as actualisations of fixed natural possibilities, known as forms. This was part of a teleological understanding of nature in which all things have an intended role to play in a divine cosmic order. In the 17th century, the new method of modern science rejected the Aristotelian approach, however, this new approach was slow to take root in the biological sciences, the last bastion of the concept of fixed natural types. The biological classification introduced by Carl Linnaeus in 1735 explicitly recognized the nature of species relationships. Other naturalists of this time speculated on the change of species over time according to natural laws
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Cambrian
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The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya and its subdivisions, and its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, as a result, our understanding of the Cambrian biology surpasses that of some later periods. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia, the seas were relatively warm, and polar ice was absent for much of the period. The United States Federal Geographic Data Committee uses a barred capital C ⟨Є⟩ character similar to the capital letter Ukrainian Ye ⟨Є⟩ to represent the Cambrian Period, the proper Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR. Despite the long recognition of its distinction from younger Ordovician Period rocks and older Supereon Precambrian rocks, the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. Pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA, the stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain. The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period, the Cambrian is divided into four epochs and ten ages. Currently only two series and five stages are named and have a GSSP, because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian, Middle Cambrian and Furongian, rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian, each of the local epochs is divided into several stages. The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago, the lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier and this formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour, though the used to obtain this number are now considered to be unsuitable. A more precise date using modern radiometric dating yield a date of 541 ±0.3 million years ago, most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian, the sea levels fluctuated somewhat, suggesting there were ice ages, associated with pulses of expansion and contraction of a south polar ice cap. In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into a epicontinental sea, the Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents
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Timeline of the evolutionary history of life
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This timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. In biology, evolution is any change across generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of organization, from kingdoms to species. The similarities between all present day organisms indicate the presence of an ancestor from which all known species, living. More than 99 percent of all species, amounting to five billion species. Estimates on the number of Earths current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. Species go extinct constantly as environments change, organisms compete for environmental niches, occasionally biodiversity on the planet takes a hit in the form of a mass extinction in which the extinction rate is much higher than usual. A large extinction event often represents an accumulation of smaller extinction events that take place in a brief period of time. The first known mass extinction in earths history was the Great Oxygenation Event 2.4 billion years ago, the event led to the loss of most of the planets obligate anaerobes. The Holocene extinction event is currently under way, in this timeline, Ma means million years ago, ka means thousand years ago, and ya means years ago. 4000 Ma –2500 Ma 2500 Ma –542 Ma, contains the Palaeoproterozoic, Mesoproterozoic and Neoproterozoic eras. 542 Ma – present The Phanerozoic Eon, literally the period of well-displayed life, marks the appearance in the record of abundant. It is subdivided into three eras, the Paleozoic, Mesozoic and Cenozoic, which are divided by mass extinctions. 542 Ma –251.0 Ma and contains the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, from 251.4 Ma to 66 Ma and containing the Triassic, Jurassic and Cretaceous periods. 66 Ma – present Dawkins, Richard, the Ancestors Tale, A Pilgrimage to the Dawn of Life. Understanding Evolution, your one-stop resource for information on evolution, explore complete phylogenetic tree interactively Brandt, Niel. Houston, TX, The TalkOrigins Foundation, Inc, interactive timeline from Big Bang to present Plant Evolution. Sequence of Plant Evolution The History of Animal Evolution, sequence of Animal Evolution Yeo, Dannel, Drage, Thomas
16.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
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Unicellular organism
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A unicellular organism, also known as a single-celled organism, is an organism that consists of only one cell, unlike a multicellular organism that consists of more than one cell. Historically, simple unicellular organisms have been referred to as monads, though this term is used more specifically to describe organisms of the genus Monas. The main groups of organisms are bacteria, archaea, protozoa, unicellular algae. Unicellular organisms fall into two categories, prokaryotic organisms and eukaryotic organisms. Unicellular organisms are thought to be the oldest form of life, prokaryotes, most Protista, and some fungi are unicellular. Although some of these live in colonies, they dont exhibit specialization. These organisms live together, and each cell in the colony is the same, however, each individual cell must carry out all life processes to survive. In contrast, even the simplest multicellular organisms have cells that depend on each other to survive, most multicellular organisms have a unicellular life-cycle stage. Gametes, for example, are reproductive unicells for multicellular organisms, additionally, multicellularity appears to have evolved independently many times in the history of life. Some organisms are partially uni- and multicellular, like Dictyostelium discoideum, additionally, unicellular organisms can be multinucleate, like Myxogastria and Plasmodium. Candidatus Magnetoglobus multicellular, related to Deltaproteobacteria, is a multicellular prokaryote and it is neither unicellular, nor a colony. Primitive cells, often referred to as protocells, are the precursors to todays unicellular organisms, the RNA world hypothesis assumes that RNA molecules could form in abiotic conditions, which would require nucleic acids and ribose to be present. Theoretical and experimental findings show that nucleic acids and sugars could have been synthesized in early prebiotic conditions, compartmentalization was necessary for chemical reactions to be more likely as well as to differentiate reactions with the external environment. For example, an early RNA replicator ribozyme may have replicated other replicator ribozymes of different RNA sequences if not kept separate, when amphiphiles like lipids are placed in water, the hydrophobic tails aggregate to form micelles and vesicles, with the hydrophilic ends facing outwards. Primitive cells likely used self-assembling fatty-acid vesicles to separate chemical reactions, because of their simplicity and ability to self-assemble in water, its likely that these simple membranes predated other forms of early biological molecules. Prokaryotes lack membrane-bound organelles, such as mitochondria or a nucleus, instead, most prokaryotes have an irregular region that contains DNA, known as the nucleoid. Most prokaryotes have a single, circular chromosome, which is in contrast to eukaryotes, nutritionally, prokaryotes have the ability to utilize a wide range of organic and inorganic material for use in metabolism, including sulfur, cellulose, ammonia, or nitrite. Prokaryotes as a whole are ubiquitous in the environment and exist in extreme environments as well, bacteria are one of the world’s oldest forms of life, and are found virtually everywhere in nature
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Evolution of photosynthesis
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The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or electrons, rather than water. There are three major metabolic pathways by which photosynthesis is carried out, C3 photosynthesis, C4 photosynthesis, C3 photosynthesis is the oldest and most common form. The biochemical capacity to use water as the source for electrons in photosynthesis evolved in an ancestor of extant cyanobacteria. The geological record indicates that this event took place early in Earths history, at least 2450–2320 million years ago. Available evidence from studies of Archean sedimentary rocks indicates that life existed 3500 Ma. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, cyanobacteria remained principal primary producers throughout the Proterozoic Eon, in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae. Early photosynthetic systems, such as those from green and purple sulfur and green and purple bacteria, are thought to have been anoxygenic. Green and purple sulfur bacteria are thought to have used hydrogen, green nonsulfur bacteria used various amino and other organic acids. Purple nonsulfur bacteria used a variety of organic molecules. Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old, the main source of oxygen in the atmosphere is oxygenic photosynthesis, and its first appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as a donor, which is oxidized to molecular oxygen in the photosynthetic reaction center. Several groups of animals have formed relationships with photosynthetic algae. These are most common in corals, sponges and sea anemones and it is presumed that this is due to the particularly simple body plans and large surface areas of these animals compared to their volumes. This allows the mollusks to survive solely by photosynthesis for several months at a time, some of the genes from the plant cell nucleus have even been transferred to the slugs, so that the chloroplasts can be supplied with proteins that they need to survive. An even closer form of symbiosis may explain the origin of chloroplasts, chloroplasts have many similarities with photosynthetic bacteria, including a circular chromosome, prokaryotic-type ribosomes, and similar proteins in the photosynthetic reaction center. The endosymbiotic theory suggests that bacteria were acquired by early eukaryotic cells to form the first plant cells
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Eukaryote
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A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, secondly, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts
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Multicellular organism
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Multicellular organisms are organisms that consist of more than one cell, in contrast to unicellular organisms. Multicellular organisms arise in different ways, for example by cell division or by aggregation of many single cells. Colonial organisms are the result of identical individuals joining together to form a colony. Multicellularity has evolved independently at least 46 times, including in some prokaryotes, like cyanobacteria, myxobacteria, actinomycetes, however, complex multicellular organisms evolved only in six eukaryotic groups, animals, fungi, brown algae, red algae, green algae, and land plants. It evolved repeatedly for Chloroplastida, once or twice for animals, once for brown algae, the first evidence of multicellularity is from cyanobacteria-like organisms that lived 3–3.5 billion years ago. To reproduce, true multicellular organisms must solve the problem of regenerating a whole organism from germ cells, animals have evolved a considerable diversity of cell types in a multicellular body, compared with 10–20 in plants and fungi. Loss of multicellularity occurred in some groups, fungi are predominantly multicellular, though early diverging lineages are largely unicellular and there have been numerous reversions to unicellularity across fungi. It may also have occurred in some red algae, but it is possible that they are primitively unicellular), loss of multicellularity is also considered probable in some green algae. In other groups, generally parasites, a reduction of multicellularity occurred, multicellular organisms, especially long-living animals, face the challenge of cancer, which occurs when cells fail to regulate their growth within the normal program of development. Changes in tissue morphology can be observed during this process, cancer in animals has often been described as a loss of multicellularity. There is a discussion about the possibility of existence of cancer in other organisms or even in protozoa. For example, plant galls have been characterized as tumors but some argue that plants do not develop cancer. In some multicellular groups, which are called Weismannists, a separation between a sterile somatic cell line and a cell line evolved. However, Weismannist development is relatively rare, as part of species have the capacity for somatic embryogenesis. One hypothesis for the origin of multicellularity is that a group of function-specific cells aggregated into a mass called a grex. This is essentially what slime molds do, another hypothesis is that a primitive cell underwent nucleus division, thereby becoming a coenocyte. A membrane would then form around each nucleus, thereby resulting in a group of connected cells in one organism and this is what plant and animal embryos do as well as colonial choanoflagellates. Because the first multicellular organisms were simple, soft organisms lacking bone, shell or other body parts
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Arthropod
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An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages. Arthropods form the phylum Arthropoda, which includes the insects, arachnids, myriapods, arthropods are characterized by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages, the rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Their versatility has enabled them to become the most species-rich members of all guilds in most environments. They have over a million described species, making up more than 80% of all described living species, some of which. Arthropods range in size from the microscopic crustacean Stygotantulus up to the Japanese spider crab, arthropods primary internal cavity is a hemocoel, which accommodates their internal organs, and through which their haemolymph – analogue of blood – circulates, they have open circulatory systems. Like their exteriors, the organs of arthropods are generally built of repeated segments. Their nervous system is ladder-like, with paired ventral nerve cords running through all segments and their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong, arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many setae that project through their cuticles. Aquatic species use internal or external fertilization. Almost all arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother, arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form. The level of care for hatchlings varies from nonexistent to the prolonged care provided by scorpions. The evolutionary ancestry of arthropods dates back to the Cambrian period, the group is generally regarded as monophyletic, and many analyses support the placement of arthropods with cycloneuralians in a superphylum Ecdysozoa. Overall however, the relationships of Metazoa are not yet well resolved. Likewise, the relationships between various groups are still actively debated. Arthropods contribute to the food supply both directly as food, and more importantly indirectly as pollinators of crops. Some species are known to spread disease to humans, livestock. The word arthropod comes from the Greek ἄρθρον árthron, joint, and πούς pous, i. e. foot or leg, arthropods are invertebrates with segmented bodies and jointed limbs
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Mollusca
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The molluscs compose the large phylum Mollusca of invertebrate animals. Around 85,000 extant species of molluscs are recognized, molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats and they are highly diverse, not just in size and in anatomical structure, but also in behaviour and in habitat. The phylum is divided into 9 or 10 taxonomic classes. The gastropods are by far the most numerous molluscs in terms of classified species, the three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula, and the structure of the nervous system. Other than these things, molluscs express great morphological diversity, so many textbooks base their descriptions on an ancestral mollusc. This has a single, limpet-like shell on top, which is made of proteins and chitin reinforced with calcium carbonate, the underside of the animal consists of a single muscular foot. Although molluscs are coelomates, the coelom tends to be small, the main body cavity is a hemocoel through which blood circulates, their circulatory systems are mainly open. The generalized mollusc has two paired nerve cords, or three in bivalves, the brain, in species that have one, encircles the esophagus. Most molluscs have eyes, and all have sensors to detect chemicals, vibrations, the simplest type of molluscan reproductive system relies on external fertilization, but more complex variations occur. All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, good evidence exists for the appearance of gastropods, cephalopods and bivalves in the Cambrian period 541 to 485.4 million years ago. Molluscs have, for centuries, also been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye and their shells have also been used as money in some preindustrial societies. Mollusc species can also represent hazards or pests for human activities, the bite of the blue-ringed octopus is often fatal, and that of Octopus apollyon causes inflammation that can last for over a month. Stings from a few species of large tropical cone shells can also kill, schistosomiasis is transmitted to humans via water snail hosts, and affects about 200 million people. Snails and slugs can also be serious pests, and accidental or deliberate introduction of some snail species into new environments has seriously damaged some ecosystems. The words mollusc and mollusk are both derived from the French mollusque, which originated from the Latin molluscus, from mollis, molluscus was itself an adaptation of Aristotles τα μαλακά, the soft things, which he applied to cuttlefish. The scientific study of molluscs is accordingly called malacology, as it is now known these groups have no relation to molluscs, and very little to one another, the name Molluscoida has been abandoned. The most universal features of the structure of molluscs are a mantle with a significant cavity used for breathing and excretion
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Evolutionary history of plants
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The ascendance of flowering plants over gymnosperms in terrestrial environments. Evidence for the appearance of the first land plants occurs in the Ordovician, around 450 million years ago and this chert, formed in volcanic hot springs, preserved several species of early plants in cellular detail by petrification. By the middle of the Devonian, many of the features recognised in plants today were present, including roots, Late Devonian free-sporing plants such as Archaeopteris had secondary vascular tissue that produced wood and had formed forests of tall trees. Also by late Devonian, Elkinsia, an early seed fern, had evolved seeds, evolutionary innovation continued into the Carboniferous and is still ongoing today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event and this may have set the scene for the appearance of the flowering plants in the Triassic, and their later diversification in the Cretaceous and Paleogene. The latest major group of plants to evolve were the grasses, the grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low CO2 and warm, dry conditions of the tropics over the last 10 million years. Land plants evolved from a group of algae, perhaps as early as 510 million years ago, some molecular estimates place their origin even earlier. Co-operative interactions with fungi may have helped early plants adapt to the stresses of the terrestrial realm and these organisms, although phylogenetically diverse, were probably small and simple, forming little more than an algal scum. The first evidence of plants on land comes from spores of mid-Ordovician age and their walls contain sporopollenin – further evidence of an embryophytic affinity. It could be that atmospheric poisoning prevented eukaryotes from colonising the land prior to this, trilete spores similar to those of vascular plants appear soon afterwards, in Upper Ordovician rocks. Depending exactly when the tetrad splits, each of the four spores may bear a trilete mark, however, this requires that the spore walls be sturdy and resistant at an early stage. This resistance is associated with having a desiccation-resistant outer wall—a trait only of use when spores must survive out of water. Indeed, even those embryophytes that have returned to the lack a resistant wall. The earliest megafossils of land plants were thalloid organisms, which dwelt in fluvial wetlands and are found to have covered most of an early Silurian flood plain and they could only survive when the land was waterlogged. Once plants had reached the land, there were two approaches to dealing with desiccation, the bryophytes avoid it or give in to it, restricting their ranges to moist settings, or drying out and putting their metabolism on hold until more water arrives. Tracheophytes also developed vascular tissue to aid in the movement of water within the organisms, vascular tissue also facilitated upright growth without the support of water and paved the way for the evolution of larger plants on land. The establishment of a land-based flora caused increased accumulation of oxygen in the atmosphere, when this concentration rose above 13%, wildfires became possible. This is first recorded in the early Silurian fossil record by charcoalified plant fossils, apart from a controversial gap in the Late Devonian, charcoal is present ever since
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Dinosaur
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Dinosaurs are a diverse group of reptiles of the clade Dinosauria that first appeared during the Triassic. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research and they became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago, until the late 20th century, all groups of dinosaurs were believed to be extinct. As such, birds were the dinosaur lineage to survive the mass extinction event. This article deals primarily with non-avian dinosaurs, Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish, using fossil evidence, paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species and fossil remains, while dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, evidence suggests that egg laying and nest building are additional traits shared by all dinosaurs.7 meters and heights of 18 meters and were the largest land animals of all time. Still, the idea that dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large. Many dinosaurs were small, Xixianykus, for example, was only about 50 cm long. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the community believed dinosaurs to have been sluggish. Most research conducted since the 1970s, however, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. The large sizes of some groups, as well as their seemingly monstrous and fantastic nature, have ensured dinosaurs regular appearance in best-selling books and films. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, the term is derived from the Greek words δεινός and σαῦρος. Though the taxonomic name has often interpreted as a reference to dinosaurs teeth, claws. Instead, dinosaurs, like many forms of reptile sub-groups, did not exhibit characteristics which were traditionally regarded as reptilian. Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of Triceratops, Neornithes, their most recent common ancestor, Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a class that had evolved from dinosaurs
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Mammal
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Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles by the possession of a neocortex, hair, three middle ear bones and mammary glands. All female mammals nurse their young with milk, secreted from the mammary glands, Mammals include the largest animals on the planet, the great whales. The basic body type is a quadruped, but some mammals are adapted for life at sea, in the air, in trees. The largest group of mammals, the placentals, have a placenta, Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale. With the exception of the five species of monotreme, all modern mammals give birth to live young, most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents, bats and Soricomorpha, the next three biggest orders, depending on the biological classification scheme used, are the Primates, the Cetartiodactyla, and the Carnivora. Living mammals are divided into the Yinotheria and Theriiformes There are around 5450 species of mammal, in some classifications, extant mammals are divided into two subclasses, the Prototheria, that is, the order Monotremata, and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the group of the Metatheria, and include all living metatherians as well as many extinct ones. Much of the changes reflect the advances of cladistic analysis and molecular genetics, findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora. The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade, the early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the line that led to todays reptiles. Some mammals are intelligent, with some possessing large brains, self-awareness, Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, most mammals are polygynous, but some can be monogamous or polyandrous. They provided, and continue to provide, power for transport and agriculture, as well as commodities such as meat, dairy products, wool. Mammals are hunted or raced for sport, and are used as model organisms in science, Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is accepted, McKenna & Bell and Wilson & Reader provide useful recent compendiums. Though field work gradually made Simpsons classification outdated, it remains the closest thing to a classification of mammals
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Flowering plant
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The flowering plants, also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 416 families, approx. 13,164 known genera and a total of c.295,383 known species, etymologically, angiosperm means a plant that produces seeds within an enclosure, in other words, a fruiting plant. The term angiosperm comes from the Greek composite word meaning enclosed seeds, the ancestors of flowering plants diverged from gymnosperms in the Triassic Period, during the range 245 to 202 million years ago, and the first flowering plants are known from 160 mya. They diversified extensively during the Lower Cretaceous, became widespread by 120 mya, angiosperms differ from other seed plants in several ways, described in the table. These distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants, the amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms. The vascular bundles of the stem are arranged such that the xylem and phloem form concentric rings, in the dicotyledons, the bundles in the very young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium, the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Among the monocotyledons, the bundles are more numerous in the stem and are scattered through the ground tissue. They contain no cambium and once formed the stem increases in diameter only in exceptional cases, the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, and provide the most trustworthy external characteristics for establishing relationships among angiosperm species, the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally on a shoot or from the axil of a leaf, occasionally, as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. There are two kinds of cells produced by flowers. Microspores, which divide to become pollen grains, are the male cells and are borne in the stamens. The female cells called megaspores, which divide to become the egg cell, are contained in the ovule. The flower may consist only of parts, as in willow. Usually, other structures are present and serve to protect the sporophylls, the individual members of these surrounding structures are known as sepals and petals. The outer series is usually green and leaf-like, and functions to protect the rest of the flower, the inner series is, in general, white or brightly colored, and is more delicate in structure. It functions to attract insect or bird pollinators, attraction is effected by color, scent, and nectar, which may be secreted in some part of the flower
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Bird
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Birds, a subgroup of Reptiles, are the last living examples of Dinosaurs. Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the class of tetrapods with the most living species, at ten thousand. Birds are the closest living relatives of crocodilians, the fossil record indicates that birds evolved from feathered ancestors within the theropod group of saurischian dinosaurs. True birds first appeared during the Cretaceous period, around 100 million years ago, Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world while diversifying during periods of global cooling. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago. Birds have wings which are more or less developed depending on the species, the digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have evolved for swimming. Many species annually migrate great distances, Birds are social, communicating with visual signals, calls, and bird songs, and participating in such social behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of species are socially monogamous, usually for one breeding season at a time, sometimes for years. Other species have breeding systems that are polygynous or, rarely, Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents, most birds have an extended period of parental care after hatching. Some birds, such as hens, lay eggs even when not fertilised, songbirds, parrots, and other species are popular as pets. Guano is harvested for use as a fertiliser, Birds prominently figure throughout human culture. About 120–130 species have become extinct due to human activity since the 17th century, human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry, the first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae. Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use, Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda, Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria
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Primate
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A primate is a mammal of the order Primates. In taxonomy, primates include two distinct lineages, strepsirrhines and haplorhines, Primates arose from ancestors that lived in the trees of tropical forests, many primate characteristics represent adaptations to life in this challenging three-dimensional environment. Most primate species remain at least partly arboreal, with the exception of humans, who inhabit every continent except for Antarctica, most primates live in tropical or subtropical regions of the Americas, Africa and Asia. Based on fossil evidence, the earliest known true primates, represented by the genus Teilhardina, an early close primate relative known from abundant remains is the Late Paleocene Plesiadapis, c. Molecular clock studies suggest that the branch may be even older. The order Primates was traditionally divided into two groupings, prosimians and anthropoids. Prosimians have characteristics more like those of the earliest primates, and include the lemurs of Madagascar, lorisoids, simians include monkeys, apes and hominins. Simians are divided into two groups, catarrhine monkeys and apes of Africa and Southeast Asia and platyrrhine or New World monkeys of South, catarrhines consist of Old World monkeys, gibbons and great apes, New World monkeys include the capuchin, howler and squirrel monkeys. Humans are the only extant catarrhines to have spread successfully outside of Africa, South Asia, New primate species are still being discovered. More than 25 species were described in the decade of the 2000s. Considered generalist mammals, primates exhibit a range of characteristics. Some primates are primarily terrestrial rather than arboreal, but all species possess adaptations for climbing trees, locomotion techniques used include leaping from tree to tree, walking on two or four limbs, knuckle-walking, and swinging between branches of trees. Primates are characterized by large brains relative to other mammals, as well as a reliance on stereoscopic vision at the expense of smell. These features are developed in monkeys and apes and noticeably less so in lorises. Three-color vision has developed in some primates, most also have opposable thumbs and some have prehensile tails. Many species are dimorphic, differences include body mass, canine tooth size. Primates have slower rates of development than other similarly sized mammals and reach maturity later, depending on the species, adults may live in solitude, in mated pairs, or in groups of up to hundreds of members. The relationships among the different groups of primates were not clearly understood until relatively recently, for example, ape has been used either as an alternative for monkey or for any tailless, relatively human-like primate
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History of Earth
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The history of Earth concerns the development of the planet Earth from its formation to the present day. Nearly all branches of science have contributed to the understanding of the main events of the Earths past. The age of Earth is approximately one-third of the age of the universe, an immense amount of geological change has occurred in that timespan, accompanied by the emergence of life and its subsequent evolution. Earth formed around 4.54 billion years ago by accretion from the solar nebula, volcanic outgassing probably created the primordial atmosphere and then the ocean, but the atmosphere contained almost no oxygen and so would have been toxic to most modern life including humans. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. A giant impact collision with a body named Theia while Earth was in its earliest stage. Over time, the Earth cooled, causing the formation of a solid crust, the geological time scale clock depicts the larger spans of time from the beginning of the Earth as well as a chronology of some definitive events of Earth history. The Archean and Proterozoic eons follow, they produced the abiogenesis of life on Earth, there are microbial mat fossils such as stromatolites found in 3.48 billion-year-old sandstone discovered in Western Australia. According to one of the researchers, If life arose relatively quickly on Earth … then it could be common in the universe, living forms derived from photosynthesis appeared between 3.2 and 2.4 billion years ago and began enriching the atmosphere with oxygen. More than 99 percent of all species, amounting to five billion species. Estimates on the number of Earths current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. Geological change has been a constant of Earths crust since the time of its formation, species continue to evolve, taking on new forms, splitting into daughter species or going extinct in the process of adapting or dying in response to ever-changing physical environments. The process of plate tectonics continues to play a dominant role in the shaping of Earths oceans and continents, in geochronology, time is generally measured in mya, each unit representing the period of approximately 1,000,000 years in the past. The history of Earth is divided into four great eons, starting 4,540 mya with the formation of the planet, each eon saw the most significant changes in Earths composition, climate and life. Each eon is divided into eras, which in turn are divided into periods. The history of the Earth can be organized according to the geologic time scale. The following four timelines show the time scale
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Age of the Earth
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The age of the Earth is 4.54 ±0.05 billion years. This dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the ages of the oldest-known terrestrial. Following the development of radiometric age-dating in the early 20th century, the oldest such minerals analyzed to date—small crystals of zircon from the Jack Hills of Western Australia—are at least 4.404 billion years old. Comparing the mass and luminosity of the Sun to those of other stars and it is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites. It is also difficult to determine the age of the oldest rocks on Earth, exposed at the surface. Studies of strata, the layering of rocks and earth, gave naturalists an appreciation that Earth may have been many changes during its existence. These layers often contained fossilized remains of creatures, leading some to interpret a progression of organisms from layer to layer. Nicolas Steno in the 17th century was one of the first naturalists to appreciate the connection between fossil remains and strata and his observations led him to formulate important stratigraphic concepts. In the 1790s, William Smith hypothesized that if two layers of rock at widely differing locations contained similar fossils, then it was plausible that the layers were the same age. William Smiths nephew and student, John Phillips, later calculated by means that Earth was about 96 million years old. In the mid-18th century, the naturalist Mikhail Lomonosov suggested that Earth had been created separately from, and several hundred years before. In 1779 the Comte du Buffon tried to obtain a value for the age of Earth using an experiment, He created a globe that resembled Earth in composition. This led him to estimate that Earth was about 75,000 years old, other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers. This was a challenge to the view, which saw the history of Earth as static. Many naturalists were influenced by Lyell to become uniformitarians who believed that changes were constant, in 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years. He assumed that Earth had formed as a completely molten object, geologists such as Charles Lyell had trouble accepting such a short age for Earth. For biologists, even 100 million years seemed much too short to be plausible, in Darwins theory of evolution, the process of random heritable variation with cumulative selection requires great durations of time. In a lecture in 1869, Darwins great advocate, Thomas H. Huxley, attacked Thomsons calculations and their values were consistent with Thomsons calculations
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Origin of water on Earth
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The origin of water on Earth, or the reason that there is clearly more liquid water on Earth than on the other rocky planets of the Solar System, is not completely understood. There exist numerous more or less mutually compatible hypotheses as to how water may have accumulated on Earths surface over the past 4.5 billion years in sufficient quantity to form oceans. Comets, trans-Neptunian objects or water-rich meteoroids from the reaches of the asteroid belt colliding with Earth may have brought water to the worlds oceans. Large enough Planetesimals were heated by the decay of aluminium isotope and this could cause water to rise to the surface. What is however unclear is whether these comets are representative of those from the Kuiper Belt, the water in carbon-rich chondrites point to a similar D/H ratio as oceanic water. Nevertheless, mechanisms have been proposed to suggest that the D/H-ratio of oceanic water may have increased significantly throughout Earths history, such a proposal is consistent with the possibility that a significant amount of the water on Earth was already present during the planets early evolution. Recent measurements of the composition of Moon rocks suggest that Earth was born with its water already present. Investigating lunar samples carried to Earth by the Apollo 15 and 17 missions found a ratio that matched the isotopic ratio in carbonaceous chondrites. The ratio is similar to that found in water on Earth. The findings suggest a common source of water for both objects and this supports a theory that Jupiter temporarily migrated into the inner Solar System, destabilizing the orbits of water-rich carbonaceous chondrites. As a result, some of the bodies could have fallen inwards and become part of the raw material for making Earth, the discovery of water vapor out-gassing from Ceres provides related information on water-ice content of the asteroid belt. Gradual leakage of stored in hydrate minerals of Earths rocks could have formed a portion of its water. Water may also have come from volcanism, water vapor in the atmosphere that originated in volcanic eruptions may have condensed to form rain, a sizeable quantity of water would have been in the material that formed Earth. Water molecules would have escaped Earths gravity more easily when it was less massive during its formation, part of the young planet is theorized to have been disrupted by the impact which created the Moon, which should have caused melting of one or two large areas. Present composition does not match complete melting and it is hard to melt, however, a fair fraction of material should have been vaporized by this impact, creating a rock-vapor atmosphere around the young planet. The rock-vapor would have condensed within two years, leaving behind hot volatiles which probably resulted in a heavy carbon dioxide atmosphere with hydrogen. Liquid water oceans existed despite the temperature of 230°C because of the atmospheric pressure of the heavy CO2 atmosphere. As cooling continued, subduction and dissolving in ocean water removed most CO2 from the atmosphere but levels oscillated wildly as new surface and mantle cycles appeared
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Earliest known life forms
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The earliest known life forms on Earth are putative fossilized microorganisms. The earliest time that life forms first appeared on Earth is unknown, a life form, or lifeform, is an entity or being that is living. Earth remains the place in the universe known to harbor life forms. More than 99% of all species of life forms, amounting to five billion species. Estimates on the number of Earths current species of life forms range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described, the total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes. In comparison, the mass of the biosphere has been estimated to be as much as 4 TtC. In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor of all living on Earth. Under certain test conditions, life forms have been observed to thrive in the vacuum of outer space, Life forms appear to thrive in the Mariana Trench, the deepest spot in the Earths oceans. In August 2014, scientists confirmed the existence of life forms living 800 m below the ice of Antarctica, fossil evidence from the Earth informs most studies of the origin of life. Microbial mat fossils have found in 3.48 billion-year-old sandstone in Western Australia. Other early physical evidence of biogenic substances includes graphite, and possibly stromatolites, remains of biotic life have been found in 4.1 billion-year-old rocks in Western Australia. In recent years, there have been a number of discoveries that suggested the earliest appearance of life on Earth was even earlier in time, according to biologist Stephen Blair Hedges, If life arose relatively quickly on Earth … then it could be common in the universe. Biota Life Vitae Wikispecies – a free directory of life
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Late Heavy Bombardment
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The Late Heavy Bombardment is an event thought to have occurred approximately 4.1 to 3.8 billion years ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. The LHB happened after the Earth and other rocky planets had formed and accreted most of their mass, Evidence for the LHB derives from lunar samples brought back by the Apollo astronauts. Isotopic dating of Moon rocks implies that most impact melts occurred in a narrow interval of time. Several hypotheses attempt to explain the apparent spike in the flux of impactors in the inner Solar System and they also note that the rate of impact cratering could differ significantly between the outer and inner zones of the Solar System. The main piece of evidence for a lunar cataclysm comes from the ages of impact melt rocks that were collected during the Apollo missions. The majority of impact melts are believed to have formed during the collision of asteroids or comets tens of kilometers across. The Apollo 15,16, and 17 landing sites were chosen as a result of their proximity to the Imbrium, Nectaris, under study on Earth, the ages of impact melts collected at these sites clustered between about 3.8 and 4.1 Ga. The apparent clustering of ages of these led to postulation that the record an intense bombardment of the Moon. They called it the lunar cataclysm and proposed that it represented an increase in the rate of bombardment of the Moon around 3.9 Ga. At the time, the conclusion was considered controversial, as more data has become available, particularly from lunar meteorites, this theory, while still controversial, has gained in popularity. The lunar meteorites are believed to randomly sample the lunar surface, many of the feldspathic lunar meteorites probably originated from the lunar far side, and impact melts within these have recently been dated. Consistent with the hypothesis, none of their ages was found to be older than about 3.9 Ga. Nevertheless, the ages do not cluster at this date. Dating of howardite, eucrite and diogenite meteorites and H chondrite meteorites originating from the asteroid belt reveal numerous ages from 3. 4–4.1 Ga, impact velocities above 10 km/s require very high inclinations or the large eccentricities of asteroids on planet crossing orbits. Such objects are rare in the current asteroid belt but the population would be increased by the sweeping of resonances due to giant planet migration. Studies of the highland crater size distributions suggest that the family of projectiles struck Mercury. The first criticism concerns the origin of the impact melt rocks that were sampled at the Apollo landing sites. While these impact melts have been attributed to having been derived from the closest basin. According to this hypothesis, the cluster of impact melt ages near 3.9 Ga simply reflects material being collected from a single impact event, Imbrium
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Geological history of oxygen
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Before photosynthesis evolved, Earths atmosphere had no free oxygen. Photosynthetic prokaryotic organisms that produced O2 as a waste product lived long before the first build-up of free oxygen in the atmosphere, the oxygen they produced would have been rapidly removed from the atmosphere by weathering of reducing minerals, most notably iron. This mass rusting led to the deposition of oxide on the ocean floor. Oxygen only began to persist in the atmosphere in small quantities about 50 million years before the start of the Great Oxygenation Event and this mass oxygenation of the atmosphere resulted in rapid buildup of free oxygen. At current rates of production, todays concentration of oxygen could be produced by photosynthetic organisms in 2,000 years.9 billion years ago. The presence of O2 provided life with new opportunities, aerobic metabolism is more efficient than anaerobic pathways, and the presence of oxygen undoubtedly created new possibilities for life to explore. Since the start of the Cambrian period, atmospheric oxygen concentrations have fluctuated between 15% and 35% of atmospheric volume. The maximum of 35% was reached towards the end of the Carboniferous period, whilst human activities, such as the burning of fossil fuels, affect relative carbon dioxide concentrations, their effect on the much larger concentration of oxygen is less significant. But Haldanes essay points out that it would apply to insects. However, the basis for this correlation is not firm. There is no significant correlation between atmospheric oxygen and maximum body size elsewhere in the geological record, ecological constraints can better explain the diminutive size of post-Carboniferous dragonflies - for instance, the appearance of flying competitors such as pterosaurs, birds and bats. The most celebrated link between oxygen and evolution occurs at the end of the last of the Snowball glaciations, where complex life is first found in the fossil record. Significant concentrations of oxygen were just one of the prerequisites for the evolution of complex life, models based on uniformitarian principles suggest that such a concentration was only reached immediately before metazoa first appeared in the fossil record. First breath, Earths billion-year struggle for oxygen New Scientist, #2746,5 February 2010 by Nick Lane, the Mystery of Earths Oxygen New York Times,3 October 2013 by Carl Zimmer
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Great Oxygenation Event
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The Great Oxygenation Event was the biologically induced appearance of dioxygen in Earths atmosphere. The current geochemical and biomarker evidence for the development of oxygenic photosynthesis before the Great Oxidation Event has been mostly inconclusive. Oceanic cyanobacteria, which evolved into multicellular forms more than 2.3 billion years ago, are believed to have become the first microbes to produce oxygen by photosynthesis, before the GOE, any free oxygen they produced was chemically captured by dissolved iron or organic matter. The GOE was the point in time when these oxygen sinks became saturated, at which point oxygen, the increased production of oxygen set Earths original atmosphere off balance. Free oxygen is toxic to anaerobic organisms, and the rising concentrations may have destroyed most such organisms at the time. Cyanobacteria were therefore responsible for one of the most significant extinction events in Earths history, besides marine cyanobacteria, there is also evidence of cyanobacteria on land. A spike in chromium contained in ancient rock deposits formed underwater shows they had accumulated chromium washed off from continental shelves, chromium is not easily dissolved and its release from rocks would have required the presence of a powerful acid. One such acid, sulfuric acid, might have created through bacterial reactions with pyrite. Eventually, the evolution of organisms that consumed oxygen established an equilibrium in its availability. Free oxygen has been an important constituent of the atmosphere ever since, the excess of oxygen those organisms produce is a waste product. These organisms lived long before the GOE, perhaps as early as 3,500 million years ago, initially, the oxygen they produced would have quickly been removed from the atmosphere by the chemical weathering of reducing minerals, most notably iron. This mass rusting led to the deposition of oxide in the form of banded-iron formations such as the sediments in Minnesota and Pilbara. Oxygen only began to persist in the atmosphere in small quantities shortly before the start of the GOE, without a mineral sink in the form of iron, oxygen could have accumulated very rapidly. For example, at rates of photosynthesis, modern atmospheric O2 levels could be produced in around 2,000 years. Another hypothesis is that producers did not evolve until just before the major rise in atmospheric oxygen concentration. This is based on interpretation of the oxygen indicator, mass-independent fractionation of sulfur isotopes. This hypothesis would eliminate the need to explain a lag in time between the evolution of oxyphotosynthetic microbes and the rise in free oxygen.4 to 2.1 billion years ago. The latter may have been a full-blown, and possibly the longest ever, snowball Earth episode, despite the natural recycling of organic matter, life had remained energetically limited until the widespread availability of oxygen
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Ediacaran biota
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The Ediacaran biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms that lived during the Ediacaran Period. Trace fossils of organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The Ediacaran biota radiated in an event called the Avalon explosion,575 million years ago, the biota largely disappeared with the rapid increase in biodiversity known as the Cambrian explosion. Most of the existing body plans of animals first appeared in the fossil record of the Cambrian rather than the Ediacaran. For macroorganisms, the Cambrian biota appears to have replaced the organisms that dominated the Ediacaran fossil record. Multiple hypotheses exist to explain the disappearance of this biota, including bias, a changing environment. The morphology and habit of some taxa suggest relationships to Porifera or Cnidaria, Kimberella may show a similarity to molluscs, and other organisms have been thought to possess bilateral symmetry, although this is controversial. Most macroscopic fossils are morphologically distinct from later life-forms, they resemble discs, tubes, one palaeontologist proposed a separate kingdom level category Vendozoa in the Linnaean hierarchy for the Ediacaran biota. The concept of Ediacaran Biota is, of course, somewhat artificial as it can not be defined geographically, stratigraphically, taphonomically, the first Ediacaran fossils discovered were the disc-shaped Aspidella terranovica in 1868. Their discoverer, Scottish geologist Alexander Murray, found them useful aids for correlating the age of rocks around Newfoundland, instead, they were interpreted as gas escape structures or inorganic concretions. No similar structures elsewhere in the world were known and the one-sided debate soon fell into obscurity. It was not until the British discovery of the iconic Charnia in 1957 that the pre-Cambrian was seriously considered as containing life. This frond-shaped fossil was found in Englands Charnwood Forest, and due to the geological mapping of the British Geological Survey there was no doubt these fossils sat in Precambrian rocks. All specimens discovered until 1967 were in coarse-grained sandstone that prevented preservation of fine details, poor communication, combined with the difficulty in correlating globally distinct formations, led to a plethora of different names for the biota. Ediacaran and Ediacarian were subsequently applied to the epoch or period of geological time, in March 2004, the International Union of Geological Sciences ended the inconsistency by formally naming the terminal period of the Neoproterozoic after the Australian locality. The term Ediacaran biota and similar has, at times, been used in a geographic, stratigraphic, taphonomic, or biological sense. Microbial mats are areas of sediment stabilised by the presence of colonies of microbes that secrete sticky fluids or otherwise bind the sediment particles. They appear to migrate upwards when covered by a layer of sediment but this is an illusion caused by the colonys growth, individuals do not, themselves
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Cambrian explosion
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Lasting for about the next 20–25 million years, it resulted in the divergence of most modern metazoan phyla. Additionally, the event was accompanied by major diversification of other organisms, prior to the Cambrian explosion, most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 to 80 million years, the rate of diversification accelerated by an order of magnitude, almost all present animal phyla appeared during this period. There is strong evidence for species of Cnidaria and Porifera existing in the Ediacaran, bryozoans dont appear in the fossil record until after the Cambrium, in the Lower Ordovician. The Cambrian explosion has generated extensive scientific debate, interpretation is difficult due to a limited supply of evidence, based mainly on an incomplete fossil record and chemical signatures remaining in Cambrian rocks. The first discovered Cambrian fossils were trilobites, described by Edward Lhuyd, nineteenth-century geologists such as Adam Sedgwick and Roderick Murchison used the fossils for dating rock strata, specifically for establishing the Cambrian and Silurian periods. He reasoned that earlier seas had swarmed with living creatures, earlier fossil evidence has since been found. Fossils of more complex cells, from which all animals, plants. Rocks dating from 580 to 543 million years ago contain fossils of the Ediacara biota, organisms so large that they are likely multicelled, the most common organism, Marrella, was clearly an arthropod, but not a member of any known arthropod class. Stephen Jay Goulds popular 1989 account of work, Wonderful Life, brought the matter into the public eye. While differing significantly in details, both Whittington and Gould proposed that all animal phyla had appeared almost simultaneously in a rather short span of geological period. Other analyses, some recent and some dating back to the 1970s. Radiometric dates for much of the Cambrian, obtained by analysis of elements contained within rocks, have only recently become available. Therefore, dates or descriptions of sequences of events should be regarded with some caution until better data become available, fossils of organisms bodies are usually the most informative type of evidence. Fossilization is an event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence, the record is very incomplete, increasingly so as earlier times are considered. Despite this, they are adequate to illustrate the broader patterns of lifes history. Also, biases exist in the record, different environments are more favourable to the preservation of different types of organism or parts of organisms
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Tetrapod
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The superclass Tetrapoda contains the four-limbed vertebrates known as tetrapods, it includes living and extinct amphibians, reptiles and mammals, as well as earlier extinct groups. The first tetrapods appeared by the late Devonian,367, the first tetrapods were primarily aquatic. Their descendants drove most amphibians to extinction as they began to dominate, the amniotes include the tetrapods that further evolved for flight—such as birds from among the dinosaurs, and bats from among the mammals. The change from a plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known. It is also becoming increasingly well-understood as a result of more transitional fossil finds, many tetrapods have returned to partially aquatic or fully aquatic lives throughout the history of the group. Tetrapods can be defined in cladistics as the nearest common ancestor of all living amphibians and all living amniotes, the group so defined is the crown group, or crown tetrapods. The term tetrapodomorph is used for the definition, any animal that is more closely related to living amphibians, reptiles, birds. The group so defined is known as the total group. Stegocephalia is a larger group equivalent to some uses of the word tetrapod. Batrachomorphs are all sharing a more recent common ancestry with living amphibians than with living amniotes. Reptiliomorphs are all sharing a more recent common ancestry with living amniotes than with living amphibians. Tetrapoda includes four classes, amphibians, reptiles, mammals, however, that diversification process was interrupted at least a few times by major biological crises, such as the Permian–Triassic extinction event, which at least affected amniotes. As biodiversity has grown, so has the number of niches that tetrapods have occupied, the first tetrapods were aquatic and fed primarily on fish. Today, the Earth supports a diversity of tetrapods that live in many habitats. Tetrapods evolved from early bony fishes, specifically from the branch of lobe-finned fishes. The first tetrapods probably evolved in the Emsian stage of the Early Devonian from Tetrapodomorph fish living in water environments. The very earliest tetrapods would have been similar to Acanthostega, with legs and lungs as well as gills. The earliest tetrapods inhabited saltwater, brackish-water, and freshwater environments and these traits were shared with many early lobed-finned fishes
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Ape
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The simians are the monkeys, cladistically including the apes, the New World monkeys or platyrrhines, and the catarrhine clade consisting of the Old World monkeys and apes. The simian line and the line diverged about 60 million years ago. Forty million years ago, simians from Africa colonized South America, the remaining simians split 25 million years ago into apes and Old World monkeys. Under modern classification, the tarsiers and simians are grouped under the suborder Haplorhini while the strepsirrhines are placed in suborder Strepsirrhini, in anthropoidea, evidences indicate that the Old and the New World primates went through parallel evolution. Primatology, paleoanthropology, and other related fields are split on their usage of the synonymous infraorder names, Simiiformes and Anthropoidea. According to Robert Hoffstetter, the term Simiiformes has priority over Anthropoidea because of the taxonomic term Simii by van der Hoeven, from which it is constructed, dates to 1833. In contrast, Anthropoidea by Mivart dates to 1864, while Simiiformes by Haeckel dates to 1866, Hoffstetter also argued that Simiiformes is also constructed like a proper infraorder name, whereas Anthropoidea ends in -oidea, which is reserved for superfamilies. He also noted that Anthropoidea is too easily confused with anthropoïdes, the simians are split into three distinct groups. The New World monkeys in parvorder Platyrrhini split from the rest of the line about 40 mya. This group split about 25 mya between the Old World monkeys and the apes
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Phanerozoic
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The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 541 million years to the present, and began with the Cambrian Period when diverse hard-shelled animals first appeared. Its name was derived from the Ancient Greek words φανερός and ζωή, meaning life, since it was once believed that life began in the Cambrian. The time before the Phanerozoic, called the Precambrian supereon, is now divided into the Hadean, Archaean, land plant life appeared in the early Phanerozoic eon. During this time span, tectonic forces caused the continents to move and eventually collect into a landmass known as Pangaea. The Proterozoic-Phanerozoic boundary is at 541 million years ago, the three different dividing points are within a few million years of each other. The Phanerozoic is divided into three eras, the Paleozoic, Mesozoic, and Cenozoic, which are subdivided into 12 periods. The Paleozoic features the rise of fish, amphibians and reptiles, the Mesozoic is ruled by the reptiles, and features the evolution of mammals, birds and more famously, dinosaurs. The Cenozoic is the time of the mammals, and more recently, the Paleozoic is a time in Earths history when complex life forms evolved, took their first breath of oxygen on dry land, and when the forerunners of all life on Earth began to diversify. There are six periods in the Paleozoic era, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, the Cambrian is the first period of the Paleozoic Era and starts from 541 to 485 million years ago. The Cambrian sparked a rapid expansion in evolution in an event known as the Cambrian Explosion during which the greatest number of creatures evolved in a period in the history of Earth. Plants like algae evolved, and the fauna was dominated by armored arthropods, almost all marine phyla evolved in this period. During this time, the super-continent Pannotia began to break up, the Ordovician spans from 485 million years to 440 million years. The Ordovician was a time in Earths history in many species still prevalent today evolved, such as primitive fish, cephalopods. The most common forms of life, however, were trilobites, snails, more importantly, the first arthropods crept ashore to colonize Gondwana, a continent empty of animal life. By the end of the Ordovican, Gondwana had moved from the equator to the South Pole, the glaciation of Gondwana resulted in a major drop in sea level, killing off all life that had established along its coast. Glaciation caused a snowball Earth, leading to the Ordovician-Silurian extinction, during which 60% of marine invertebrates and this is considered the first mass extinction and the second deadliest in the history of Earth. The Silurian spans from 440 million years to 415 million years, fully terrestrial life evolved, which included early arachnids, fungi, and centipedes
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Proterozoic
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The Proterozoic is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic comes from Greek and means life, the Greek root protero-, means former, earlier and zoic-, means animal. The Proterozoic Eon extended from 2500 Ma to 541 Ma, and is the most recent part of the Precambrian Supereon and it is subdivided into three geologic eras, the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. The geologic record of the Proterozoic Eon is more complete than that for the preceding Archean Eon, studies of these rocks have shown that the eon continued the massive continental accretion that had begun late in the Archean Eon. The Proterozoic Eon also featured the first definitive supercontinent cycles and wholly modern mountain building activity, there is evidence that the first known glaciations occurred during the Proterozoic. One of the most important events of the Proterozoic was the accumulation of oxygen in the Earths atmosphere, until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level. The Banded iron formations, which provide most of the iron ore, are one mark of that mineral sink process. Their accumulation ceased after 1.9 billion years ago, after the iron in the oceans had all been oxidized, red beds, which are colored by hematite, indicate an increase in atmospheric oxygen 2 billion years ago. Such massive iron oxide formations are not found in older rocks, the Proterozoic Eon was a very tectonically active period in the Earth’s history. The late Archean Eon to Early Proterozoic Eon corresponds to a period of increasing crustal recycling, suggesting subduction, evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6 Ga. The appearance of eclogites, which metamorphic rocks created by pressure, are explained using a model that incorporates subduction. As a result of remelting of basaltic oceanic crust due to subduction, the long-term tectonic stability of those cratons is why we find continental crust ranging up to a few billion years in age. It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, studies by Condie 2000 and Rino et al.2004 suggest that crust production happened episodically. By isotopically calculating the ages of Proterozoic granitoids it was determined there were several episodes of rapid increase in continental crust production. The reason for these pulses is unknown, but they seemed to have decreased in magnitude after every period, evidence of collision and rifting between continents raises the question as to what exactly were the movements of the Archean cratons composing Proterozoic continents. Paleomagnetic and geochronological dating mechanisms have allowed the deciphering of Precambrian Supereon tectonics and it is known that tectonic processes of the Proterozoic Eon resemble greatly the evidence of tectonic activity, such as orogenic belts or ophiolite complexes, we see today. Hence, most geologists would conclude that the Earth was active at that time and it is also commonly accepted that during the Precambrian, the Earth went through several supercontinent breakup and rebuilding cycles. In the late Proterozoic, the dominant supercontinent was Rodinia and it consisted of a series of continents attached to a central craton that forms the core of the North American Continent called Laurentia
