Absolute dating
Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word implies a unwarranted certainty of accuracy. Absolute dating provides an age or range in contrast with relative dating which places events in order without any measure of the age between events. Techniques include tree rings in timbers, radiocarbon dating of wood or bones, radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes. Particular isotopes are suitable for different applications due to the type of atoms present in the mineral or other material, one of the most widely used and well-known absolute dating techniques is carbon-14 dating, which is used to date organic remains. This is a technique since it is based on radioactive decay. Cosmic radiation entering the earth’s atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide, carbon-14 moves up the food chain as animals eat plants and as predators eat other animals.
With death, the uptake of carbon-14 stops and it takes 5,730 years for half the carbon-14 to change to nitrogen, this is the half-life of carbon-14. After another 5,730 years only one-quarter of the original carbon-14 will remain, after yet another 5,730 years only one-eighth will be left. By measuring the carbon-14 in organic material, scientists can determine the date of death of the matter in an artifact or ecofact. The relatively short half-life of carbon-14,5,730 years, an additional problem with carbon-14 dates from archeological sites is known as the old wood problem. Thus dating that particular tree does not necessarily indicate when the fire burned or the structure was built, for this reason, many archaeologists prefer to use samples from short-lived plants for radiocarbon dating. The development of mass spectrometry dating, which allows a date to be obtained from a very small sample, has been very useful in this regard. Other radiometric dating techniques are available for earlier periods, one of the most widely used is potassium-argon dating.
Potassium-40 is an isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated. Argon, a gas, is not commonly incorporated into such samples except when produced in situ through radioactive decay. The date measured reveals the last time that the object was heated past the closure temperature at which the trapped argon can escape the lattice, k-Ar dating was used to calibrate the geomagnetic polarity time scale
Accretion (astrophysics)
In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk. Most astronomical objects, such as galaxies and planets, are formed by accretion processes, the idea proposed in the 19th century that Earth and the other terrestrial planets formed from meteoric material was developed in a quantitative way in 1969 by Viktor Safronov. He calculated, in detail, the different stages of planet formation. Since then, the theory has been developed using intensive numerical simulations to study planetesimal accumulation. Stars form by the collapse of interstellar gas. Prior to collapse, this gas is mostly in the form of molecular clouds, as the cloud collapses, losing potential energy, it heats up, gaining kinetic energy, and the conservation of angular momentum ensures that the cloud forms a flatted disk—the accretion disk. A few hundred years after the Big Bang, the Universe cooled to the point where atoms could form.
As the Universe continued to expand and cool, the atoms lost enough kinetic energy, as further accretion occurred, galaxies formed. Galaxies grow through mergers and smooth gas accretion, accretion occurs inside galaxies, forming stars. Stars are thought to form inside giant clouds of cold molecular hydrogen—giant molecular clouds of roughly 300,000 M☉ and 65 light-years in diameter, over millions of years, giant molecular clouds are prone to collapse and fragmentation. These fragments form small, dense cores, which in turn collapse into stars, the cores range in mass from a fraction to several times that of the Sun and are called protostellar nebulae. They possess diameters of 2, 000–20,000 astronomical units, compare it with the particle number density of the air at the sea level—2. 8×1019/cm3. The initial collapse of a solar-mass protostellar nebula takes around 100,000 years, every nebula begins with a certain amount of angular momentum. This core forms the seed of what will become a star, as the collapse continues, conservation of angular momentum dictates that the rotation of the infalling envelope accelerates, which eventually forms a disk.
Around this time the protostar begins to fuse deuterium, if the protostar is sufficiently massive, hydrogen fusion follows. Otherwise, if its mass is too low, the object becomes a brown dwarf and this birth of a new star occurs approximately 100,000 years after the collapse begins. Objects at this stage are known as Class I protostars, which are called young T Tauri stars, evolved protostars, or young stellar objects. By this time, the star has already accreted much of its mass
Radioactive decay
A material containing such unstable nuclei is considered radioactive. Certain highly excited short-lived nuclear states can decay through neutron emission, or more rarely, for a collection of atoms, the collections expected decay rate is characterized in terms of their measured decay constants or half-lives. This is the basis of radiometric dating, the half-lives of radioactive atoms have no known upper limit, spanning a time range of over 55 orders of magnitude, from nearly instantaneous to far longer than the age of the universe. A radioactive nucleus with spin can have no defined orientation. If there are multiple particles produced during a single decay, as in decay, their relative angular distribution. Such a parent process could be a previous decay, or a nuclear reaction, the decaying nucleus is called the parent radionuclide, and the process produces at least one daughter nuclide. Except for gamma decay or internal conversion from an excited state. When the number of changes, an atom of a different chemical element is created.
The first decay processes to be discovered were alpha decay, beta decay, alpha decay occurs when the nucleus ejects an alpha particle. This is the most common process of emitting nucleons, but highly excited nuclei can eject single nucleons, or in the case of cluster decay, specific light nuclei of other elements. Beta decay occurs when the nucleus emits an electron or positron, the nucleus may capture an orbiting electron, causing a proton to convert into a neutron in a process called electron capture. All of these result in a well-defined nuclear transmutation. By contrast, there are radioactive decay processes that do not result in a nuclear transmutation, another type of radioactive decay results in products that vary, appearing as two or more fragments of the original nucleus with a range of possible masses. For a summary table showing the number of stable and radioactive nuclides in each category, there are 29 naturally occurring chemical elements on Earth that are radioactive. They are those that contain 34 radionuclides that date before the time of formation of the solar system, well-known examples are uranium and thorium, but included are naturally occurring long-lived radioisotopes, such as potassium-40.
Radioactivity was discovered in 1896 by the French scientist Henri Becquerel and these materials glow in the dark after exposure to light, and he suspected that the glow produced in cathode ray tubes by X-rays might be associated with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it, all results were negative until he used uranium salts. The uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper and these radiations were given the name Becquerel Rays
Diorite
Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate, between that of gabbro and felsic granite. Diorite is usually grey to dark-grey in colour, but it can be black or bluish-grey and it is distinguished from gabbro on the basis of the composition of the plagioclase species, the plagioclase in diorite is richer in sodium and poorer in calcium. Diorite may contain small amounts of quartz and olivine, apatite, magnetite and sulfides occur as accessory minerals. Minor amounts of muscovite may be present, varieties deficient in hornblende and other dark minerals are called leucodiorite. When olivine and more iron-rich augite are present, the grades into ferrodiorite. The presence of significant quartz makes the rock type quartz-diorite or tonalite, and if orthoclase is present at greater than 10 percent, a dioritic rock containing feldspathoid mineral/s and no quartz is termed foid-bearing diorite or foid diorite according to content.
Diorite has a phaneritic, often speckled, texture of coarse grain size and is occasionally porphyritic, orbicular diorite shows alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus, within a diorite porphyry matrix. Diorites may be associated with granite or gabbro intrusions, into which they may subtly merge. Diorite results from the melting of a mafic rock above a subduction zone. It is commonly produced in volcanic arcs, and in mountain building, such as in the Andes Mountains. The extrusive volcanic equivalent rock type is andesite, diorite is an extremely hard rock, making it difficult to carve grand work with. It is so hard that ancient civilizations used diorite balls to work granite and its hardness, allows it to be worked finely and take a high polish, and to provide a durable finished work. One comparatively frequent use of diorite was for inscription, as it is easier to carve in relief than in three-dimensional statuary, perhaps the most famous diorite work extant is the Code of Hammurabi, inscribed upon a 2.23 m pillar of black diorite.
The original can be today in Paris Musée du Louvre. The use of diorite in art was most important among very early Middle Eastern civilizations such as Ancient Egypt, Babylonia and Sumer. It was so valued in early times that the first great Mesopotamian empire—the Empire of Sargon of Akkad—listed the taking of diorite as a purpose of military expeditions. Although one can find diorite art from periods, it more popular as a structural stone and was frequently used as pavement due to its durability
Cenozoic
The Cenozoic Era is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 66 million years ago to the present day. The Cenozoic is known as the Age of Mammals, because of the mammals that dominated, such as Entelodont, Paraceratherium. The extinction of many large groups such as non-avian dinosaurs and Pterosauria allowed the mammals and birds to greatly diversify. Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including mammals, reptiles. From a geological perspective, it did not take long for mammals, some flightless birds grew larger than humans. These species are referred to as terror birds, and were formidable predators. Mammals came to occupy almost every available niche, and some grew very large, the Earths climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum.
The continents began looking roughly familiar at this time and moved into their current positions. The Cenozoic is divided into three periods, the Paleogene and Quaternary, and seven epochs, the Paleocene, Oligocene, Pliocene and Holocene. The common use of epochs during the Cenozoic helps paleontologists better organize, there is more detailed knowledge of this era than any other because of the relatively young, well-preserved rocks associated with it. The Paleogene spans from the extinction of dinosaurs,66 million years ago. It features three epochs, the Paleocene and Oligocene, the Paleocene ranged from 66 million to 56 million years ago. The Paleocene is a point between the devastation that is the K-T extinction, to the rich jungles environment that is the Early Eocene. The Early Paleocene saw the recovery of the earth, the continents began to take their modern shape, but all the continents and subcontinent India were separated from each other. Afro-Eurasia was separated by the Tethys Sea, and the Americas were separated by the strait of Panama and this epoch featured a general warming trend, with jungles eventually reaching the poles.
The oceans were dominated by sharks as the large reptiles that had once ruled became extinct, archaic mammals filled the world such as creodonts and early primates that evolved during the Mesozoic, and as a result, there was nothing over 10 kilograms. The Eocene Epoch ranged from 56 million years to 33.9 million years ago, in the Early-Eocene, life was small and lived in cramped jungles, much like the Paleocene. There was nothing over the weight of 10 kilograms, among them were early primates and horses along with many other early forms of mammals
Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in both South America and Latin America. As the worlds fifth-largest country by area and population, it is the largest country to have Portuguese as an official language. Its Amazon River basin includes a vast tropical forest, home to wildlife, a variety of ecological systems. This unique environmental heritage makes Brazil one of 17 megadiverse countries, Brazil was inhabited by numerous tribal nations prior to the landing in 1500 of explorer Pedro Álvares Cabral, who claimed the area for the Portuguese Empire. Brazil remained a Portuguese colony until 1808, when the capital of the empire was transferred from Lisbon to Rio de Janeiro, in 1815, the colony was elevated to the rank of kingdom upon the formation of the United Kingdom of Portugal and the Algarves. Independence was achieved in 1822 with the creation of the Empire of Brazil, a state governed under a constitutional monarchy. The ratification of the first constitution in 1824 led to the formation of a bicameral legislature, the country became a presidential republic in 1889 following a military coup détat.
An authoritarian military junta came to power in 1964 and ruled until 1985, Brazils current constitution, formulated in 1988, defines it as a democratic federal republic. The federation is composed of the union of the Federal District, the 26 states, Brazils economy is the worlds ninth-largest by nominal GDP and seventh-largest by GDP as of 2015. A member of the BRICS group, Brazil until 2010 had one of the worlds fastest growing economies, with its economic reforms giving the country new international recognition. Brazils national development bank plays an important role for the economic growth. Brazil is a member of the United Nations, the G20, BRICS, Mercosul, Organization of American States, Organization of Ibero-American States, CPLP. Brazil is a power in Latin America and a middle power in international affairs. One of the worlds major breadbaskets, Brazil has been the largest producer of coffee for the last 150 years and it is likely that the word Brazil comes from the Portuguese word for brazilwood, a tree that once grew plentifully along the Brazilian coast.
In Portuguese, brazilwood is called pau-brasil, with the word brasil commonly given the etymology red like an ember, formed from Latin brasa and the suffix -il. As brazilwood produces a red dye, it was highly valued by the European cloth industry and was the earliest commercially exploited product from Brazil. The popular appellation eclipsed and eventually supplanted the official Portuguese name, early sailors sometimes called it the Land of Parrots. In the Guarani language, a language of Paraguay, Brazil is called Pindorama
Anorthosite
Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar, and a minimal mafic component. Pyroxene, ilmenite and olivine are the minerals most commonly present. Anorthosite on Earth can be divided into two types, Proterozoic anorthosite and Archean anorthosite and these two types of anorthosite have different modes of occurrence, appear to be restricted to different periods in Earths history, and are thought to have had different origins. Lunar anorthosites constitute the areas of the Moons surface and have been the subject of much research. Proterozoic anorthosites were emplaced during the Proterozoic Eon, Anorthosite plutons occur in a wide range of sizes. Some smaller plutons, exemplified by many bodies in the U. S. and Harris in Scotland. Larger plutons, like the Mt. Lister Anorthosite, in northern Labrador, many Proterozoic anorthosites occur in spatial association with other highly distinctive, contemporaneous rock types. These rock types include iron-rich diorite and norite, leucocratic mafic rocks such as leucotroctolite and leuconorite, large volumes of ultramafic rocks are not found in association with Proterozoic anorthosites.
Occurrences of Proterozoic anorthosites are commonly referred to as massifs, there is some question as to what name would best describe any occurrence of anorthosite together with the rock types mentioned above. Batholith is used to such occurrences for the remainder of this article. The areal extent of anorthosite batholiths ranges from small to nearly 20,000 km2, in the instance of the Nain Plutonic Suite in northern Labrador. Major occurrences of Proterozoic anorthosite are found in the southwest U. S. the Appalachian Mountains, eastern Canada, across southern Scandinavia and eastern Europe. Mapped onto the Pangaean continental configuration of that eon, these occurrences are all contained in a single straight belt, the conditions and constraints of this pattern of origin and distribution are not clear. However, see the Origins section below, Anorthosites are common in layered intrusions. Anorthosite in these layered intrusions can form as cumulate layers in the parts of the intrusive complex or as later-stage intrusions into the layered intrusion complex.
Since they are composed of plagioclase feldspar, most of Proterozoic anorthosites appear, in outcrop. Individual plagioclase crystals may be black, blue, or grey, the feldspar variety labradorite is commonly present in anorthosites. Mineralogically, labradorite is a term for any calcium-rich plagioclase feldspar containing 50–70 molecular percent anorthite
Volcano
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Earths volcanoes occur because its crust is broken into 17 major, therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. This type of volcanism falls under the umbrella of plate hypothesis volcanism, Volcanism away from plate boundaries has been explained as mantle plumes. These so-called hotspots, for example Hawaii, are postulated to arise from upwelling diapirs with magma from the boundary,3,000 km deep in the Earth. Volcanoes are usually not created where two plates slide past one another. Erupting volcanoes can pose hazards, not only in the immediate vicinity of the eruption. Historically, so-called volcanic winters have caused catastrophic famines, the word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology.
The study of volcanoes is called volcanology, sometimes spelled vulcanology, at the mid-oceanic ridges, two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock. Most divergent plate boundaries are at the bottom of the oceans, most volcanic activity is submarine, black smokers are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the temperature of the overlying mantle wedge. This magma tends to be very viscous due to its high content, so it often does not reach the surface. When it does reach the surface, a volcano is formed, typical examples of this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire.
Because tectonic plates move across them, each volcano becomes dormant and is eventually re-formed as the plate advances over the postulated plume and this theory is currently under criticism, however. The most common perception of a volcano is of a mountain, spewing lava and poisonous gases from a crater at its summit, however. The features of volcanoes are more complicated and their structure. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have features such as massive plateaus
Structure of the Earth
The interior structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by their chemical and their rheological properties, Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. The force exerted by Earths gravity can be used to calculate its mass, astronomers can calculate Earths mass by observing the motion of orbiting satellites. Earth’s average density can be determined through gravitometric experiments, which have historically involved pendulums, the mass of Earth is about 6×1024 kg. The structure of Earth can be defined in two ways, by properties such as rheology, or chemically. Mechanically, it can be divided into lithosphere, mesospheric mantle, outer core, Earth can be divided into the crust, upper mantle, lower mantle, outer core, and inner core. The core does not allow shear waves to pass through it, the changes in seismic velocity between different layers causes refraction owing to Snells law, like light bending as it passes through a prism.
Likewise, reflections are caused by an increase in seismic velocity and are similar to light reflecting from a mirror. The crust ranges from 5–70 kilometres in depth and is the outermost layer, the thin parts are the oceanic crust, which underlie the ocean basins and are composed of dense iron magnesium silicate igneous rocks, like basalt. The thicker crust is continental crust, which is dense and composed of sodium potassium aluminium silicate rocks. The rocks of the crust fall into two major categories – sial and sima and it is estimated that sima starts about 11 km below the Conrad discontinuity. The uppermost mantle together with the crust constitutes the lithosphere, the crust-mantle boundary occurs as two physically different events. First, there is a discontinuity in the velocity, which is most commonly known as the Mohorovičić discontinuity or Moho. The cause of the Moho is thought to be a change in composition from rocks containing plagioclase feldspar to rocks that contain no feldspars.
Earths mantle extends to a depth of 2,890 km, the mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone, the lowest part of the mantle next to the core-mantle boundary is known as the D″ layer. The pressure at the bottom of the mantle is ≈140 GPa, the mantle is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the temperatures within the mantle cause the silicate material to be sufficiently ductile that it can flow on very long timescales
Africa
Africa is the worlds second-largest and second-most-populous continent. At about 30.3 million km² including adjacent islands, it covers 6% of Earths total surface area and 20.4 % of its land area. With 1.2 billion people as of 2016, it accounts for about 16% of the human population. The continent includes Madagascar and various archipelagos and it contains 54 fully recognized sovereign states, nine territories and two de facto independent states with limited or no recognition. Africas population is the youngest amongst all the continents, the age in 2012 was 19.7. Algeria is Africas largest country by area, and Nigeria by population, Homo erectus, H. habilis and H. ergaster – with the earliest Homo sapiens found in Ethiopia being dated to circa 200,000 years ago. Africa straddles the equator and encompasses numerous climate areas, it is the continent to stretch from the northern temperate to southern temperate zones. Africa hosts a diversity of ethnicities and languages. In the late 19th century European countries colonized most of Africa, Africa varies greatly with regard to environments, historical ties and government systems.
However, most present states in Africa originate from a process of decolonization in the 20th century, afri was a Latin name used to refer to the inhabitants of Africa, which in its widest sense referred to all lands south of the Mediterranean. This name seems to have referred to a native Libyan tribe. The name is connected with Hebrew or Phoenician ʿafar dust. The same word may be found in the name of the Banu Ifran from Algeria and Tripolitania, under Roman rule, Carthage became the capital of the province of Africa Proconsularis, which included the coastal part of modern Libya. The Latin suffix -ica can sometimes be used to denote a land, the Muslim kingdom of Ifriqiya, modern-day Tunisia, preserved a form of the name. According to the Romans, Africa lay to the west of Egypt, while Asia was used to refer to Anatolia, as Europeans came to understand the real extent of the continent, the idea of Africa expanded with their knowledge. 25,4, whose descendants, he claimed, had invaded Libya, isidore of Seville in Etymologiae XIV.5.2.
Suggests Africa comes from the Latin aprica, meaning sunny, massey, in 1881, stated that Africa is derived from the Egyptian af-rui-ka, meaning to turn toward the opening of the Ka. The Ka is the double of every person and the opening of the Ka refers to a womb or birthplace
Komatiite
Komatiite is a type of ultramafic mantle-derived volcanic rock. Komatiites have low silicon and aluminium, and high to extremely high magnesium content, komatiite was named for its type locality along the Komati River in South Africa. True komatiites are very rare and essentially restricted to rocks of Archean age and this restriction in age is thought to be due to cooling of the mantle, which may have been up to 500 °C hotter during the early to middle Archaean. The early Earth had much higher heat production, due to the heat from planetary accretion. Geographically, komatiites are restricted in distribution to the Archaean shield areas, Komatiites occur with other ultramafic and high-magnesian mafic volcanic rocks in Archaean greenstone belts. The youngest komatiites are from the island of Gorgona on the Caribbean oceanic plateau off the Pacific coast of Colombia, magmas of komatiitic compositions have a very high melting point, with calculated eruption temperatures in excess of 1600 °C. Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C, the higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth.
Komatiitic lava was extremely fluid when it erupted, the major komatiitic sequences preserved in Archaean rocks are thus considered to be lava tubes, ponds of lava etc. where the komatiitic lava accumulated. Komatiite chemistry is different from that of basaltic and other common mantle-produced magmas, Komatiites are considered to have been formed by high degrees of partial melting, usually greater than 50%, and hence have high MgO with low K2O and other incompatible elements. There are two classes of komatiite, aluminium undepleted komatiite and aluminium depleted komatiite, defined by their Al2O3/TiO2 ratios. These two classes of komatiite are often assumed to represent a real petrological source difference between the two related to depth of melt generation. Komatiites probably form in extremely hot mantle plumes, boninite magmatism is similar to komatiite magmatism but is produced by fluid-fluxed melting above a subduction zone. Boninites with 10–18% MgO tend to have higher large-ion lithophile elements than komatiites, the pristine volcanic mineralogy of komatiites is composed of forsteritic olivine and often chromian pyroxene and chromite. A considerable population of komatiite examples show a cumulate texture and morphology, the usual cumulate mineralogy is highly magnesium rich forsterite olivine, though chromian pyroxene cumulates are possible.
Volcanic rocks rich in magnesium may be produced by accumulation of olivine phenocrysts in basalt melts of normal chemistry, the often rarely preserved flow top breccia and pillow margin zones in some komatiite flows are essentially volcanic glass, quenched in contact with overlying water or air. Because they are cooled, they represent the liquid composition of the komatiites. The spinifex texture is named after an Australian grass that grows in clumps with similar shapes, primary mineral species encountered in komatiites include olivine, the pyroxenes augite and bronzite, chromite and rarely pargasitic amphibole. Secondary minerals include serpentine, amphibole, sodic plagioclase, iron oxides and rarely phlogopite, all known komatites have been metamorphosed, therefore should technically be termed metakomatiite though the prefix meta is inevitably assumed
Siberia
Siberia is an extensive geographical region, and by the broadest definition is known as North Asia. Siberia has historically been a part of Russia since the 17th century, the territory of Siberia extends eastwards from the Ural Mountains to the watershed between the Pacific and Arctic drainage basins. It stretches southwards from the Arctic Ocean to the hills of north-central Kazakhstan and to the borders of Mongolia. With an area of 13.1 million square kilometres, Siberia accounts for 77% of Russias land area and this is equivalent to an average population density of about 3 inhabitants per square kilometre, making Siberia one of the most sparsely populated regions on Earth. If it were a country by itself, it would still be the largest country in area, the origin of the name is unknown. Some sources say that Siberia originates from the Siberian Tatar word for sleeping land, another account sees the name as the ancient tribal ethnonym of the Sirtya, a folk, which spoke a language that evolved into the Ugric languages.
This ethnic group was assimilated to the Siberian Tatar people. The modern usage of the name was recorded in the Russian language after the Empires conquest of the Siberian Khanate, a further variant claims that the region was named after the Xibe people. The Polish historian Chycliczkowski has proposed that the name derives from the word for north. He said that the neighbouring Chinese and Mongolians would not have known Russian and he suggests that the name is a combination of two words, su and bir. The region is of significance, as it contains bodies of prehistoric animals from the Pleistocene Epoch. Specimens of Goldfuss cave lion cubs and another woolly mammoth from Oymyakon, a rhinoceros from the Kolyma River. The Siberian Traps were formed by one of the largest known volcanic events of the last 500 million years of Earths geological history. They continued for a million years and are considered a cause of the Great Dying about 250 million years ago. At least three species of human lived in Southern Siberia around 40,000 years ago, H. sapiens, H. neanderthalensis, the last was determined in 2010, by DNA evidence, to be a new species.
Siberia was inhabited by different groups of such as the Enets, the Nenets, the Huns, the Scythians. The Khan of Sibir in the vicinity of modern Tobolsk was known as a prominent figure who endorsed Kubrat as Khagan of Old Great Bulgaria in 630, the Mongols conquered a large part of this area early in the 13th century. With the breakup of the Golden Horde, the autonomous Khanate of Sibir was established in the late 15th century, turkic-speaking Yakut migrated north from the Lake Baikal region under pressure from the Mongol tribes during the 13th to 15th century
