Geological history of Earth
The geological history of Earth follows the major events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers. Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which created the rest of the Solar System. Earth was molten due to extreme volcanism and frequent collisions with other bodies; the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards as a result of the impact of a planetoid with the Earth. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans; as the surface continually reshaped itself over hundreds of millions of years, continents formed and broke apart. They migrated across the surface combining to form a supercontinent.
750 million years ago, the earliest-known supercontinent Rodinia, began to break apart. The continents recombined to form Pannotia, 600 to 540 million years ago finally Pangaea, which broke apart 200 million years ago; the present pattern of ice ages began about 40 million years ago intensified at the end of the Pliocene. The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40,000–100,000 years; the last glacial period of the current ice age ended about 10,000 years ago. The Precambrian includes 90% of geologic time, it extends from 4.6 billion years ago to the beginning of the Cambrian Period. It includes three eons, the Hadean and Proterozoic. Major volcanic events altering the Earth's environment and causing extinctions may have occurred 10 times in the past 3 billion years. During Hadean time, the Solar System was forming within a large cloud of gas and dust around the sun, called an accretion disc from which Earth formed 4,500 million years ago; the Hadean Eon is not formally recognized, but it marks the era before we have adequate record of significant solid rocks.
The oldest dated zircons date from about 4,400 million years ago. Earth was molten due to extreme volcanism and frequent collisions with other bodies; the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards as a result of the impact of a large planetoid with the Earth; some of this object's mass merged with the Earth altering its internal composition, a portion was ejected into space. Some of the material survived to form an orbiting moon. More recent potassium isotopic studies suggest that the Moon was formed by a smaller, high-energy, high-angular-momentum giant impact cleaving off a significant portion of the Earth. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans. During the Hadean the Late Heavy Bombardment occurred during which a large number of impact craters are believed to have formed on the Moon, by inference on Earth, Mercury and Mars as well.
The Earth of the early Archean may have had a different tectonic style. During this time, the Earth's crust cooled enough that continental plates began to form; some scientists think because the Earth was hotter, that plate tectonic activity was more vigorous than it is today, resulting in a much greater rate of recycling of crustal material. This may have prevented cratonisation and continent formation until the mantle cooled and convection slowed down. Others argue that the subcontinental lithospheric mantle is too buoyant to subduct and that the lack of Archean rocks is a function of erosion and subsequent tectonic events. In contrast to the Proterozoic, Archean rocks are heavily metamorphized deep-water sediments, such as graywackes, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks; the high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent deep-sea sediments eroded from the neighboring island rocks and deposited in a forearc basin.
In short, greenstone belts represent sutured protocontinents. The Earth's magnetic field was established 3.5 billion years ago. The solar wind flux was about 100 times the value of the modern Sun, so the presence of the magnetic field helped prevent the planet's atmosphere from being stripped away, what happened to the atmosphere of Mars. However, the field strength was lower than at present and the magnetosphere was about half the modern radius; the geologic record of the Proterozoic is more complete than that for the preceding Archean. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive shallow epicontinental seas. Study of these rocks show that the eon featured massive, rapid continental accretion, supercontinent cycles, wholly modern orogenic activity. 750 million years ago, the earliest-known supercontinent Rodinia, began to break apart. The continents recombined to form Pannotia, 600–540 Ma; the first-known glaciations occurred during the Proterozoic, one began shortly after the beginning of the eon, while there were at least four during the Neoproterozoic, cl
Limestone is a carbonate sedimentary rock, composed of the skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. A related rock is dolostone, which contains a high percentage of the mineral dolomite, CaMg2. In fact, in old USGS publications, dolostone was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones. About 10% of sedimentary rocks are limestones; the solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Limestone has numerous uses: as a building material, an essential component of concrete, as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.
Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as foraminifera; these organisms secrete shells made of aragonite or calcite, leave these shells behind when they die. Other carbonate grains composing limestones are ooids, peloids and extraclasts. Limestone contains variable amounts of silica in the form of chert or siliceous skeletal fragment, varying amounts of clay and sand carried in by rivers; some limestones do not consist of grains, are formed by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters; this produces speleothems, such as stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance; the primary source of the calcite in limestone is most marine organisms. Some of these organisms can construct mounds of rock building upon past generations. Below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone does not form in deeper waters.
Limestones may form in lacustrine and evaporite depositional environments. Calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors with weathered surfaces. Limestone may be crystalline, granular, or massive, depending on the method of formation. Crystals of calcite, dolomite or barite may line small cavities in the rock; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution supersaturated with the chemical constituents of calcite.
Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the mountain building process, limestone recrystallizes into marble. Limestone is a parent material of Mollisol soil group. Two major classification schemes, the Folk and the Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks. Based on composition, there are three main components: allochems and cement; the Folk system uses two-part names. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample; the Dunham scheme focuses on depositional textures. Each name is based upon the texture of the grains. Robert J. Dunham published his system for limestone in 1962.
Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles. Dunham names are for rock families, his efforts deal with the question of whether or not the grains were in mutual contact, therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock; the Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright, it adds some diagenetic patterns and can be summarized as follows: See: Carbonate platform About 10% of all sedimentary rocks are limestones. Limestone is soluble in acid, therefore forms many erosional landforms; these include limestone pavements, pot holes, cenotes and gorges. Such erosion landscapes are known
Europe is a continent located in the Northern Hemisphere and in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west and the Mediterranean Sea to the south, it comprises the westernmost part of Eurasia. Since around 1850, Europe is most considered to be separated from Asia by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas and the waterways of the Turkish Straits. Although the term "continent" implies physical geography, the land border is somewhat arbitrary and has been redefined several times since its first conception in classical antiquity; the division of Eurasia into two continents reflects East-West cultural and ethnic differences which vary on a spectrum rather than with a sharp dividing line. The geographic border does not follow political boundaries, with Turkey and Kazakhstan being transcontinental countries. A strict application of the Caucasus Mountains boundary places two comparatively small countries and Georgia, in both continents.
Europe covers 2 % of the Earth's surface. Politically, Europe is divided into about fifty sovereign states of which the Russian Federation is the largest and most populous, spanning 39% of the continent and comprising 15% of its population. Europe had a total population of about 741 million as of 2016; the European climate is affected by warm Atlantic currents that temper winters and summers on much of the continent at latitudes along which the climate in Asia and North America is severe. Further from the sea, seasonal differences are more noticeable than close to the coast. Europe, in particular ancient Greece, was the birthplace of Western civilization; the fall of the Western Roman Empire in 476 AD and the subsequent Migration Period marked the end of ancient history and the beginning of the Middle Ages. Renaissance humanism, exploration and science led to the modern era. Since the Age of Discovery started by Portugal and Spain, Europe played a predominant role in global affairs. Between the 16th and 20th centuries, European powers controlled at various times the Americas all of Africa and Oceania and the majority of Asia.
The Age of Enlightenment, the subsequent French Revolution and the Napoleonic Wars shaped the continent culturally and economically from the end of the 17th century until the first half of the 19th century. The Industrial Revolution, which began in Great Britain at the end of the 18th century, gave rise to radical economic and social change in Western Europe and the wider world. Both world wars took place for the most part in Europe, contributing to a decline in Western European dominance in world affairs by the mid-20th century as the Soviet Union and the United States took prominence. During the Cold War, Europe was divided along the Iron Curtain between NATO in the West and the Warsaw Pact in the East, until the revolutions of 1989 and fall of the Berlin Wall. In 1949 the Council of Europe was founded, following a speech by Sir Winston Churchill, with the idea of unifying Europe to achieve common goals, it includes all European states except for Belarus and Vatican City. Further European integration by some states led to the formation of the European Union, a separate political entity that lies between a confederation and a federation.
The EU originated in Western Europe but has been expanding eastward since the fall of the Soviet Union in 1991. The currency of most countries of the European Union, the euro, is the most used among Europeans. In classical Greek mythology, Europa was a Phoenician princess; the word Europe is derived from her name. The name contains the elements εὐρύς, "wide, broad" and ὤψ "eye, countenance", hence their composite Eurṓpē would mean "wide-gazing" or "broad of aspect". Broad has been an epithet of Earth herself in the reconstructed Proto-Indo-European religion and the poetry devoted to it. There have been attempts to connect Eurṓpē to a Semitic term for "west", this being either Akkadian erebu meaning "to go down, set" or Phoenician'ereb "evening, west", at the origin of Arabic Maghreb and Hebrew ma'arav. Michael A. Barry, professor in Princeton University's Near Eastern Studies Department, finds the mention of the word Ereb on an Assyrian stele with the meaning of "night, sunset", in opposition to Asu " sunrise", i.e. Asia.
The same naming motive according to "cartographic convention" appears in Greek Ἀνατολή. Martin Litchfield West stated that "phonologically, the match between Europa's name and any form of the Semitic word is poor." Next to these hypotheses there is a Proto-Indo-European root *h1regʷos, meaning "darkness", which produced Greek Erebus. Most major world languages use words derived from Europa to refer to the continent. Chinese, for example, uses the word Ōuzhōu. In some Turkic languages the Persian name Frangistan is used casually in referring to much of Europe, besides official names such as Avrupa or Evropa; the prevalent definition of Europe as a geographical term has been in use since the mid-19th century. Europe is taken to be bounded by large bodies of water
Russia the Russian Federation, is a transcontinental country in Eastern Europe and North Asia. At 17,125,200 square kilometres, Russia is by far or by a considerable margin the largest country in the world by area, covering more than one-eighth of the Earth's inhabited land area, the ninth most populous, with about 146.77 million people as of 2019, including Crimea. About 77 % of the population live in the European part of the country. Russia's capital, Moscow, is one of the largest cities in the world and the second largest city in Europe. Extending across the entirety of Northern Asia and much of Eastern Europe, Russia spans eleven time zones and incorporates a wide range of environments and landforms. From northwest to southeast, Russia shares land borders with Norway, Estonia, Latvia and Poland, Ukraine, Azerbaijan, China and North Korea, it shares maritime borders with Japan by the Sea of Okhotsk and the U. S. state of Alaska across the Bering Strait. However, Russia recognises two more countries that border it, Abkhazia and South Ossetia, both of which are internationally recognized as parts of Georgia.
The East Slavs emerged as a recognizable group in Europe between the 3rd and 8th centuries AD. Founded and ruled by a Varangian warrior elite and their descendants, the medieval state of Rus arose in the 9th century. In 988 it adopted Orthodox Christianity from the Byzantine Empire, beginning the synthesis of Byzantine and Slavic cultures that defined Russian culture for the next millennium. Rus' disintegrated into a number of smaller states; the Grand Duchy of Moscow reunified the surrounding Russian principalities and achieved independence from the Golden Horde. By the 18th century, the nation had expanded through conquest and exploration to become the Russian Empire, the third largest empire in history, stretching from Poland on the west to Alaska on the east. Following the Russian Revolution, the Russian Soviet Federative Socialist Republic became the largest and leading constituent of the Union of Soviet Socialist Republics, the world's first constitutionally socialist state; the Soviet Union played a decisive role in the Allied victory in World War II, emerged as a recognized superpower and rival to the United States during the Cold War.
The Soviet era saw some of the most significant technological achievements of the 20th century, including the world's first human-made satellite and the launching of the first humans in space. By the end of 1990, the Soviet Union had the world's second largest economy, largest standing military in the world and the largest stockpile of weapons of mass destruction. Following the dissolution of the Soviet Union in 1991, twelve independent republics emerged from the USSR: Russia, Belarus, Uzbekistan, Azerbaijan, Kyrgyzstan, Tajikistan and the Baltic states regained independence: Estonia, Lithuania, it is governed as a federal semi-presidential republic. Russia's economy ranks as the twelfth largest by nominal GDP and sixth largest by purchasing power parity in 2018. Russia's extensive mineral and energy resources are the largest such reserves in the world, making it one of the leading producers of oil and natural gas globally; the country is one of the five recognized nuclear weapons states and possesses the largest stockpile of weapons of mass destruction.
Russia is a great power as well as a regional power and has been characterised as a potential superpower. It is a permanent member of the United Nations Security Council and an active global partner of ASEAN, as well as a member of the Shanghai Cooperation Organisation, the G20, the Council of Europe, the Asia-Pacific Economic Cooperation, the Organization for Security and Co-operation in Europe, the World Trade Organization, as well as being the leading member of the Commonwealth of Independent States, the Collective Security Treaty Organization and one of the five members of the Eurasian Economic Union, along with Armenia, Belarus and Kyrgyzstan; the name Russia is derived from Rus', a medieval state populated by the East Slavs. However, this proper name became more prominent in the history, the country was called by its inhabitants "Русская Земля", which can be translated as "Russian Land" or "Land of Rus'". In order to distinguish this state from other states derived from it, it is denoted as Kievan Rus' by modern historiography.
The name Rus itself comes from the early medieval Rus' people, Swedish merchants and warriors who relocated from across the Baltic Sea and founded a state centered on Novgorod that became Kievan Rus. An old Latin version of the name Rus' was Ruthenia applied to the western and southern regions of Rus' that were adjacent to Catholic Europe; the current name of the country, Россия, comes from the Byzantine Greek designation of the Rus', Ρωσσία Rossía—spelled Ρωσία in Modern Greek. The standard way to refer to citizens of Russia is rossiyane in Russian. There are two Russian words which are commonly
Hylonomus is an extinct genus of reptile that lived 312 million years ago during the Late Carboniferous period. It is the earliest unquestionable reptile; the only species is the type species Hylonomous lyelli. Hylonomus was 20–25 centimetres long. Most of them are 20 cm long and would have looked rather similar to modern lizards, it had small sharp teeth and it ate small invertebrates such as millipedes or early insects. Fossils of Hylonomus have been found in the remains of fossilized club moss stumps in the Joggins Formation, Nova Scotia, Canada, it is supposed that, after harsh weather, the club mosses would crash down, with the stumps rotting and hollowing out. Small animals such as Hylonomus, seeking shelter, would become trapped, starving to death. An alternative hypothesis is. Fossils of the basal pelycosaur Archaeothyris and the basal diapsid Petrolacosaurus are found in the same region of Nova Scotia, although from a higher stratum, dated 6 million years later. Fossilized footprints found in New Brunswick have been attributed to Hylonomus, at an estimated age of 315 million years.
This animal was discovered by John William Dawson in the mid-19th century. The species' name was given it by the geologist Sir Charles Lyell. While it has traditionally been included in the group Protothyrididae studies have shown that it is more related to diapsids. Hylonomus lyelli was named the Provincial Fossil of Nova Scotia in 2002. Fossils of Nova Scotia - The Tree Stump Animals Transitional Vertebrate Fossils FAQ Part 1B Early Researchers & Finds of the Joggins Fossil Cliffs The Science of the Joggins Fossil Cliffs Hylonomus: Provincial Fossil of Nova Scotia A photograph of the disarticulated skeleton, credited to J. Calder Another photo of the specimen, from Dr. Melissa Grey's twitter account
Sauropsida is a taxonomic clade that consists of reptiles, including birds, the extinct Parareptilia. All living sauropsids are members of the subgroup Diapsida, the Parareptilia having died out 200 million years ago; the term originated in 1864 with Thomas Henry Huxley, who grouped birds with reptiles based on fossil evidence. Sauropsids are the sister taxon to synapsids, or "mammal-like reptiles", some of which evolved into mammals; the term Sauropsida has a long history, hails back to Thomas Henry Huxley, his opinion that birds had risen from the dinosaurs. He based this chiefly on the fossils of Hesperornis and Archaeopteryx, that were starting to become known at the time. In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Huxley grouped the vertebrate classes informally into mammals and ichthyoids, based on the gaps in physiological traits and lack of transitional fossils that seem to exist between the three groups. Early in the following year he proposed the names Ichthyopsida for the two latter.
Huxley did however include groups on the mammalian line like Dicynodon among the sauropsids. Thus, under the original definition, Sauropsida contained not only the groups associated with it today, but several groups that today are known to be in the mammalian side of the tree. By the early 20th century, the fossils of Permian synapsids from South Africa had become well known, allowing palaeontologists to trace synapsid evolution in much greater detail; the term Sauropsida was taken up by E. S. Goodrich in 1916 much like Huxley's, to include lizards and their relatives, he distinguished them from mammals and their extinct relatives, which he included in the sister group Theropsida. Goodrich's classification thus differs somewhat from Huxley's, in which the non-mammalian synapsids fell under the sauropsids. Goodrich supported this division by the nature of the hearts and blood vessels in each group, other features such as the structure of the forebrain. According to Goodrich, both lineages evolved from an earlier stem group, the Protosauria, which included some Paleozoic amphibians as well as early reptiles predating the sauropsid/synapsid split.
In 1956, D. M. S. Watson observed that sauropsids and synapsids diverged early in the reptilian evolutionary history, so he divided Goodrich's Protosauria between the two groups, he reinterpreted the Sauropsida and Theropsida to exclude birds and mammals making them paraphyletic, unlike Goodrich's definition. Thus his Sauropsida included Procolophonia, Millerosauria, Squamata, Crocodilia, "thecodonts", non-avian dinosaurs, pterosaurs and sauropyterygians; this classification supplemented, but was never as popular as, the classification of the reptiles into four subclasses according to the positioning of temporal fenestrae, openings in the sides of the skull behind the eyes. Since the advent of phylogenetic nomenclature, the term Reptilia has fallen out of favor with many taxonomists, who have used Sauropsida in its place to include a monophyletic group containing the traditional reptiles and the birds; the class Reptilia has been known to be an evolutionary grade rather than a clade for as long as evolution has been recognised.
Reclassifying reptiles has been among the key aims of phylogenetic nomenclature. The term Sauropsida had from the mid 20th century been used to denote all species not on the synapsid side after the synapsid/sauropsid split, a branch-based clade; this group encompasses all now-living reptiles as well as birds, as such is comparable to Goodrich's classification, the difference being that better resolution of the early amniote tree has split up most of the Goodrich's "Protosauria", though definitions of Sauropsida identical to Huxley's are forwarded. Some cladistic work has used Sauropsida more restrictively, to signify the crown group, i.e. all descendants of the last common ancestor of extant reptiles and birds. A number of phylogenetic stem and crown definitions have been published, anchored in a variety of fossil and extant organisms, thus there is no consensus of the actual definition of Sauropsida as a phylogenetic unit; some taxonomists, such as Benton, have co-opted the term to fit into traditional rank-based classifications, making Sauropsida and Synapsida class-level taxa to replace the traditional Class Reptilia, while Modesto and Anderson, using the PhyloCode standard, have suggested replacing the name Sauropsida with their redefinition of Reptilia, arguing that the latter is by far better known and should have priority.
Sauropsids evolved from basal amniotes stock 320 million years ago in the Paleozoic Era. In the Mesozoic Era, sauropsids were the largest animals on land, in the water, in the air; the Mesozoic is sometimes called the Age of Reptiles. Sixty-six million years ago, the large-bodied sauropsids died out in the global extinction event at the end of the Mesozoic era. With the exception of a few species of birds, the entire dinosaur lineage became extinct; the cladogram presented here illustrates the "family tree" of sauropsids, follows a sim
Geochronology is the science of determining the age of rocks and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as palaeomagnetism and stable isotope ratios. By combining multiple geochronological indicators the precision of the recovered age can be improved. Geochronology is different in application from biostratigraphy, the science of assigning sedimentary rocks to a known geological period via describing and comparing fossil floral and faunal assemblages. Biostratigraphy does not directly provide an absolute age determination of a rock, but places it within an interval of time at which that fossil assemblage is known to have coexisted. Both disciplines work together hand in hand, however, to the point where they share the same system of naming rock layers and the time spans utilized to classify layers within a stratum; the science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.
By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material. A number of radioactive isotopes are used for this purpose, depending on the rate of decay, are used for dating different geological periods. More decaying isotopes are useful for longer periods of time, but less accurate in absolute years. With the exception of the radiocarbon method, most of these techniques are based on measuring an increase in the abundance of a radiogenic isotope, the decay-product of the radioactive parent isotope. Two or more radiometric methods can be used in concert to achieve more robust results. Most radiometric methods are suitable for geological time only, but some such as the radiocarbon method and the 40Ar/39Ar dating method can be extended into the time of early human life and into recorded history; some of the used techniques are: Radiocarbon dating. This technique measures the decay of carbon-14 in organic material and can be best applied to samples younger than about 60,000 years.
Uranium–lead dating. This technique measures the ratio of two lead isotopes to the amount of uranium in a mineral or rock. Applied to the trace mineral zircon in igneous rocks, this method is one of the two most used for geologic dating. Monazite geochronology is another example of U–Pb dating, employed for dating metamorphism in particular. Uranium–lead dating is applied to samples older than about 1 million years. Uranium–thorium dating; this technique is used to date speleothems, corals and fossil bones. Its range is from a few years to about 700,000 years. Potassium–argon dating and argon–argon dating; these techniques date metamorphic and volcanic rocks. They are used to date volcanic ash layers within or overlying paleoanthropologic sites; the younger limit of the argon–argon method is a few thousand years. Electron spin resonance dating A series of related techniques for determining the age at which a geomorphic surface was created, or at which surficial materials were buried. Exposure dating uses the concentration of exotic nuclides produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface, such as an alluvial fan, was created.
Burial dating uses the differential radioactive decay of 2 cosmogenic elements as a proxy for the age at which a sediment was screened by burial from further cosmic rays exposure. Luminescence dating techniques observe'light' emitted from materials such as quartz, diamond and calcite. Many types of luminescence techniques are utilized in geology, including optically stimulated luminescence, cathodoluminescence, thermoluminescence. Thermoluminescence and optically stimulated luminescence are used in archaeology to date'fired' objects such as pottery or cooking stones and can be used to observe sand migration. Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed or floating. Dendrochronology Ice cores Lichenometry Varves A sequence of paleomagnetic poles, which are well defined in age, constitutes an apparent polar wander path; such a path is constructed for a large continental block. APWPs for different continents can be used as a reference for newly obtained poles for the rocks with unknown age.
For paleomagnetic dating, it is suggested to use the APWP in order to date a pole obtained from rocks or sediments of unknown age by linking the paleopole to the nearest point on the APWP. Two methods of paleomagnetic dating have been suggested Rotation method. First method is used for paleomagnetic dating of rocks inside of the same continental block; the second method is used for the folded areas. Magnetostratigraphy determines age from the pattern of magnetic polarity zones in a series of bedded sedimentary and/or volcanic rocks by comparison to the magnetic polarity timescale; the polarity timescale has been determined by dating of seafloor magnetic anomalies, radiometrically dating volcanic rocks within magnetostratigraphic sections, astronomically dating magnetostratigraphic sections. Global trends in isotope compositions Carbon 13 and strontium isotopes, can be used to corr