The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, where rocks from this period were first studied; the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established. Fish reached substantial diversity during this time, leading the Devonian to be dubbed the "Age of Fishes." The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating every known aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral and pelvic fins evolved into legs.
In the oceans, primitive sharks became more numerous than in the Late Ordovician. The first ammonites, species of molluscs, appeared. Trilobites, the mollusc-like brachiopods and the great coral reefs, were still common; the Late Devonian extinction which started about 375 million years ago affected marine life, killing off all placodermi, all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, the early formation of the small continent of Euramerica in between; the period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough.
Murchison and Sedgwick named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, the latter three of which are placed in the Devonian; the Devonian has erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed during its epochs and between geographic regions.
For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, North America, China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common; the Devonian Period is formally broken into Early and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early DevonianThe Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago. During this time, the first ammonoids appeared. Ammonoids during this time period differed little from their nautiloid counterparts; these ammonoids belong to the order Agoniatitida, which in epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida.
This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments due to drastic environmental changes and due to the increasing competition and diversity of jawed fishes; the shallow, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, the ability to crawl out of the water and onto the land for short periods of time. Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivisi
Saltasaurus is a genus of titanosaurid sauropod dinosaur of the Late Cretaceous Period of Argentina. Small among sauropods, though still heavy by the standards of modern creatures, Saltasaurus was characterized by a short neck and stubby limbs, it was the first genus of sauropod known to possess armour of bony plates embedded in its skin. Such small bony plates, called osteoderms, have since been found on other titanosaurids; the fossils of Saltasaurus were excavated by José Fernando Bonaparte, Martín Vince and Juan C. Leal between 1975 and 1977 at the Estancia "El Brete"; the find. Saltasaurus was named and described by Bonaparte and Jaime E. Powell in 1980; the type species is Saltasaurus loricatus. Its generic name is derived from Salta Province, the region of north-west Argentina where the first fossils were recovered; the specific name means "protected by small armoured plates" in Latin. The holotype, PVL 4017-92, was found in a layer of the Lecho Formation dating from the early Maastrichtian stage of the Upper Cretaceous period, about seventy million years old.
It consists of a sacrum connected to two ilia. Under the inventory number PVL 4017 over two hundred additional fossils have been catalogued; these include rear skull elements, vertebrae of the neck, back and tail, parts of the shoulder girdle and the pelvis, limb bones — plus various pieces of armour. These bones represent a minimum of two adults and three juveniles or subadults; the only recognised species of Saltasaurus is S. loricatus. A S. robustus and a S. australis have been suggested but these are now considered to belong to a separate genus, Neuquensaurus. Earlier, armour plates from the area had been named as Loricosaurus by Friedrich von Huene who assumed them to be from an armoured ankylosaurian, it has been suggested. Saltasaurus is small compared to most other members of the Sauropoda. Powell estimated the adult length at six metres. In 2010, Gregory S. Paul estimated the maximum length at the weight at 2.5 tonnes. However, Donald Henderson in 2013 estimated the animal at 12.8 metres in length and 6.87 tonnes in weight.
The teeth of Saltasaurus were cylindrical, with spatulate points. Saltasaurus had a short neck with shortened neck vertebrae; the vertebrae from the middle part of its tail had elongated centra. Saltasaurus had vertebral lateral fossae, that resembled shallow depressions. Fossae that resemble shallow depressions are known from Malawisaurus, Alamosaurus and Gondwanatitan. Venenosaurus had depression-like fossae, but its pleurocoels penetrated deeper into the vertebrae, were divided into two chambers, extend farther into the vertebral columns. In Saltasaurus, the vertebral bone was cancellous and there were larger air chambers present as well; the limbs were short and stubby with short hands and feet. Saltasaurus had more robust radii than Venenosaurus; the belly was wide. The osteoderms came in two types. There were larger oval plates with a length of up to twelve centimetres; these were keeled or spiked and were ordered in longitudinal rows along the back. The second type consists of small ossicles, rounded or pentagonal, about seven millimetres in diameter, that formed a continuous armour between the plates.
A study in 2010 concluded that the larger plates had cancellous bone but that the ossicles had a denser bone tissue. Like all sauropods, Saltasaurus was herbivorous; because of its barrel-like rump, shaped like a hippopotamus, Powell suggested that Saltasaurus was aquatic. Despite its small stature, Saltasaurus was still graviportal like other sauropods, meaning it could not run because its hindlimbs had to be held straight at the load-bearing phase of their walking cycle. Powell assumed adult individuals were protected against predators by their body armour, while juveniles were protected by the herd as a whole. In the Cretaceous Period, sauropods in North America were no longer the dominant group of herbivorous dinosaurs, with the ornithopod and ceratopsian dinosaurs, such as Edmontosaurus and Triceratops, becoming the most abundant. However, on other landmasses such as South America and Africa sauropods, in particular the titanosaurs continued to be the dominant herbivores. Saltasaurus was one such titanosaur sauropod, lived around 70 million years ago.
When it was first discovered, in 1975, it forced palaeontologists to reconsider some assumptions about sauropods as Saltasaurus possessed crocodile-like armour 10 to 12 centimetres in diameter. It had been assumed that size alone was sufficient defence for the massive sauropods. Since palaeontologists have investigated the possibility that other sauropods may have had armour. A new discovery, from another formation, may shed light on the nesting habits of Saltasaurus. A large titanosaurid nesting ground was discovered in Patagonia, Argentina. Several hundred female saltasaurines dug holes with their back feet, laid eggs in clutches averaging around 25 eggs each, buried the nests under dirt and vegetation; the small eggs, about 11–12 cm in diameter, contained fossilised embryos, complete with skin impressions showing a mosaic armour of small bead-like scales. The armour pattern resembled that of Saltasaurus. Coria, R. A. and Chiappe, L. M. 2007. Embryonic Skin From Late Cretaceous Sauropods of Auca Mahuevo, Argent
Dongyangosaurus is a genus of saltasaurid sauropod dinosaur from the early Late Cretaceous. The only species is Dongyangosaurus sinensis, from which only a single fragmentary skeleton is known, coming from the Zhejiang province of eastern China, it was described and named by Lü Junchang and colleagues Like other sauropods, Dongyangosaurus would have been a large quadrupedal herbivore. The only skeleton is stored in the Dongyang Museum, it consists of ten dorsal vertebrae, the sacrum, two caudal vertebrae as well as the complete pelvis. The skeleton was found articulated. Dongyangosaurus was a midsized sauropod, measuring 50 ft in length and 15 ft in height; the dorsal vertebrae were characterized by eye shaped low bifurcated neural spines. The sacrum consisted of six fused sacral vertebrae, a feature unique to somphospondylans; the caudal vertebrae were amphicoelous. The pubis was shorter than the ischium; the obturator foramen extended. When this genus was first described, it was thought to be a titanosauriform of uncertain placement.
More however, it was found to be a saltasaurid related to the Mongolian sauropod Opisthocoelicaudia. The Upper Cretaceous of Zhejiang is known for its fossil dinosaur eggs. Skeletal remains are found. Dongyangosaurus comes from the Fangyan Formation; the age of this unit is not clear yet. The specimen was found in the village of Baidian within the city of Dongyang, from which the generic name is derived; the specific name, sinensis, is Greek for from'China'
Macronaria is a clade of the "suborder" Sauropodomorpha. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located. Fossil evidence suggests that macronarian dinosaurs lived from the Late Jurassic through the Late Cretaceous. Macronarians have been found globally, including discoveries in Argentina, the United States, Portugal and Tanzania. Like other sauropods, they are known to have inhabited terrestrial areas, little evidence exists to suggest that they spent much time in coastal environments. Macronarians are diagnosed through their distinct characters on their skulls, as well as appendicular and vertebral characters. Macronaria is composed of several subclades and families notably including Camarasauridae and Titanosauriformes, among several others. Titanosauriforms are well known for being some of the largest terrestrial animals to exist. Macronaria was described by Wilson and Sereno who proposed the new subdivisions among the clade Neosauropoda.
This clade was thought to have Brachiosaurus and Camarasauridae forming one sister group, Titanosauroidea and Diplodocoidea forming another. This proposed shift with Macronaria placed Diplodocoidea as an outgroup to the new clade Macronaria, under which all other neosauropods would fall. Several synapomorphies, characteristics passed down from ancestral species, exist for Macronaria; the following list includes some of the distinguishing characteristics that are diagnostic for Macronaria: The long axis of the distal ischial shaft lie on the same plane Middle and posterior neural spines have distal ends that extend out transversely Posterior neural spines extend at the tip forming a triangular process upwards. The anterior chevrons of the tail have open proximal articulation Robust and broad-crowned teeth Crests formed by large protruding nasal Elongate metacarpals Forelimbs are long in comparison to the hind limbs The posture of macronarians is characterized by a novel ‘wide-gauged’ locomotor style in titanosaurs.
While sauropods are known to be the giants of the dinosaurs, macronarians were not large-bodied. Macronarians show divergence in the evolution of body size with some members both increasing and decreasing in size from the primitive condition. For example, despite all being in the titanosaur clade, Argentinosaurus reached enormous sizes, while Saltasaurus and Magyarosaurus reached only 1.5-3 metric tons, small for sauropods. While some macronarians represent some of the largest terrestrial vertebrates known, other macronarians experienced a steady size decrease over time. Sauropods speaking, have been associated with both coastal and inland environments, it is believed that macronarians such as titanosaurs were terrestrial and associated with inland environments such as lacustrine systems. These findings are based on ‘wide-gauged’ trackways produced by titanosaurs which are correlated with terrestrial sediments, it is believed that macronarians have Gondwanan origins. Camarasaurus is among the most found dinosaur from the Late Jurassic deposits of the Morrison Formation in the US.
Unlike Camarasaurus, Titanosaurs were most found in the Southern Hemisphere with the exception of Alamosaurus, found in North America. There is strong geologic evidence that a land bridge between South and North America existed at the end of the Cretaceous allowing for dispersal of organisms between the two landmasses. Cretaceous sauropods are thought to have moved northward from South America, thus explaining the high density of South American sauropods, the sole appearance of Alamosaurus in the Western Interior, it is well established. Unlike their sister group, the diplodocids, which were thought to feed on low-lying plants and other macronarians had upward-oriented necks for browsing trees and taller plants; each tooth family in Camarasaurus is thought to have had a maximum of three replacement teeth and tooth formation took about 315 days. The replacement rate is thought to be one tooth every 62 days – this is about the same level or higher than non-sauropod herbivores, though it is lower than the replacement rates of the sister taxa, Diplodocus.
It is thought that this may be related to the fact that the low-browsing taxa ingested more grit and thus needed to replace teeth more, while Camarasaurus and other macronarians fed on mid to upper canopy plants where exogenous grit is non-existent. Given the large body size of these neosauropod herbivores, it is thought that this type of niche partitioning, characterized by different species taking advantage of different resources, was necessary for coexistence, it was at one point believed that polished pebbles found with sauropod skeletons were gastroliths. Gastroliths are stones intentionally swallowed to aid with digestion. However, more recent taphonomic and sedimentological evidence suggests that sauropods did not use stones for digestion due to the general rarity of finding gastric mill-like stones with sauropod remains, low relative mass of the stones to the size of sauropod bodies; when gastrolith-like rocks are found with sauropods, it may be that they were accidentally ingested, or intentionally ingested for mineral uptake.
Macronaria is sister to Diplodocoidea. These groups split
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
Asia is Earth's largest and most populous continent, located in the Eastern and Northern Hemispheres. It shares the continental landmass of Eurasia with the continent of Europe and the continental landmass of Afro-Eurasia with both Europe and Africa. Asia covers an area of 44,579,000 square kilometres, about 30% of Earth's total land area and 8.7% of the Earth's total surface area. The continent, which has long been home to the majority of the human population, was the site of many of the first civilizations. Asia is notable for not only its overall large size and population, but dense and large settlements, as well as vast populated regions, its 4.5 billion people constitute 60% of the world's population. In general terms, Asia is bounded on the east by the Pacific Ocean, on the south by the Indian Ocean, on the north by the Arctic Ocean; the border of Asia with Europe is a historical and cultural construct, as there is no clear physical and geographical separation between them. It has moved since its first conception in classical antiquity.
The division of Eurasia into two continents reflects East–West cultural and ethnic differences, some of which vary on a spectrum rather than with a sharp dividing line. The most accepted boundaries place Asia to the east of the Suez Canal separating it from Africa. China and India alternated in being the largest economies in the world from 1 to 1800 CE. China was a major economic power and attracted many to the east, for many the legendary wealth and prosperity of the ancient culture of India personified Asia, attracting European commerce and colonialism; the accidental discovery of a trans-Atlantic route from Europe to America by Columbus while in search for a route to India demonstrates this deep fascination. The Silk Road became the main east–west trading route in the Asian hinterlands while the Straits of Malacca stood as a major sea route. Asia has exhibited economic dynamism as well as robust population growth during the 20th century, but overall population growth has since fallen. Asia was the birthplace of most of the world's mainstream religions including Hinduism, Judaism, Buddhism, Taoism, Islam, Sikhism, as well as many other religions.
Given its size and diversity, the concept of Asia—a name dating back to classical antiquity—may have more to do with human geography than physical geography. Asia varies across and within its regions with regard to ethnic groups, environments, historical ties and government systems, it has a mix of many different climates ranging from the equatorial south via the hot desert in the Middle East, temperate areas in the east and the continental centre to vast subarctic and polar areas in Siberia. The boundary between Asia and Africa is the Red Sea, the Gulf of Suez, the Suez Canal; this makes Egypt a transcontinental country, with the Sinai peninsula in Asia and the remainder of the country in Africa. The border between Asia and Europe was defined by European academics; the Don River became unsatisfactory to northern Europeans when Peter the Great, king of the Tsardom of Russia, defeating rival claims of Sweden and the Ottoman Empire to the eastern lands, armed resistance by the tribes of Siberia, synthesized a new Russian Empire extending to the Ural Mountains and beyond, founded in 1721.
The major geographical theorist of the empire was a former Swedish prisoner-of-war, taken at the Battle of Poltava in 1709 and assigned to Tobolsk, where he associated with Peter's Siberian official, Vasily Tatishchev, was allowed freedom to conduct geographical and anthropological studies in preparation for a future book. In Sweden, five years after Peter's death, in 1730 Philip Johan von Strahlenberg published a new atlas proposing the Urals as the border of Asia. Tatishchev announced; the latter had suggested the Emba River as the lower boundary. Over the next century various proposals were made until the Ural River prevailed in the mid-19th century; the border had been moved perforce from the Black Sea to the Caspian Sea into which the Ural River projects. The border between the Black Sea and the Caspian is placed along the crest of the Caucasus Mountains, although it is sometimes placed further north; the border between Asia and the region of Oceania is placed somewhere in the Malay Archipelago.
The Maluku Islands in Indonesia are considered to lie on the border of southeast Asia, with New Guinea, to the east of the islands, being wholly part of Oceania. The terms Southeast Asia and Oceania, devised in the 19th century, have had several vastly different geographic meanings since their inception; the chief factor in determining which islands of the Malay Archipelago are Asian has been the location of the colonial possessions of the various empires there. Lewis and Wigen assert, "The narrowing of'Southeast Asia' to its present boundaries was thus a gradual process." Geographical Asia is a cultural artifact of European conceptions of the world, beginning with the Ancient Greeks, being imposed onto other cultures, an imprecise concept causing endemic contention about what it means. Asia does not correspond to the cultural borders of its various types of constituents. From the time of Herodotus a minority of geographers have rejected the three-continent system on the grounds that there is no substantial physical separation between
Mongolia is a landlocked country in East Asia. Its area is equivalent with the historical territory of Outer Mongolia, that term is sometimes used to refer to the current state, it is sandwiched between China to Russia to the north. Mongolia does not share a border with Kazakhstan. At 1,564,116 square kilometres, Mongolia is the 18th-largest and the most sparsely populated sovereign state in the world, with a population of around three million people, it is the world's second-largest landlocked country behind Kazakhstan and the largest landlocked country that does not border a closed sea. The country contains little arable land, as much of its area is covered by grassy steppe, with mountains to the north and west and the Gobi Desert to the south. Ulaanbaatar, the capital and largest city, is home to about 45% of the country's population. Ulaanbaatar shares the rank of the world's coldest capital city with Moscow and Nur-Sultan. 30% of the population is nomadic or semi-nomadic. The majority of its population are Buddhists.
The non-religious population is the second largest group. Islam is the dominant religion among ethnic Kazakhs; the majority of the state's citizens are of Mongol ethnicity, although Kazakhs and other minorities live in the country in the west. Mongolia joined the World Trade Organization in 1997 and seeks to expand its participation in regional economic and trade groups; the area of what is now Mongolia has been ruled by various nomadic empires, including the Xiongnu, the Xianbei, the Rouran, the Turkic Khaganate, others. In 1206, Genghis Khan founded the Mongol Empire, which became the largest contiguous land empire in history, his grandson Kublai Khan conquered China to establish the Yuan dynasty. After the collapse of the Yuan, the Mongols retreated to Mongolia and resumed their earlier pattern of factional conflict, except during the era of Dayan Khan and Tumen Zasagt Khan. In the 16th century, Tibetan Buddhism began to spread in Mongolia, being further led by the Manchu-founded Qing dynasty, which absorbed the country in the 17th century.
By the early 1900s one-third of the adult male population were Buddhist monks. After the collapse of the Qing dynasty in 1911, Mongolia declared independence, achieved actual independence from the Republic of China in 1921. Shortly thereafter, the country came under the control of the Soviet Union, which had aided its independence from China. In 1924, the Mongolian People's Republic was founded as a socialist state. After the anti-Communist revolutions of 1989, Mongolia conducted its own peaceful democratic revolution in early 1990; this led to a multi-party system, a new constitution of 1992, transition to a market economy. Homo erectus inhabited Mongolia from 850,000 years ago. Modern humans reached Mongolia 40,000 years ago during the Upper Paleolithic; the Khoit Tsenkher Cave in Khovd Province shows lively pink and red ochre paintings of mammoths, bactrian camels, ostriches, earning it the nickname "the Lascaux of Mongolia". The venus figurines of Mal'ta testify to the level of Upper Paleolithic art in northern Mongolia.
Neolithic agricultural settlements, such as those at Norovlin, Tamsagbulag and Rashaan Khad, predated the introduction of horse-riding nomadism, a pivotal event in the history of Mongolia which became the dominant culture. Horse-riding nomadism has been documented by archeological evidence in Mongolia during the Copper and Bronze Age Afanasevo culture; the wheeled vehicles found in the burials of the Afanasevans have been dated to before 2200 BC. Pastoral nomadism and metalworking became more developed with the Okunev culture, Andronovo culture and Karasuk culture, culminating with the Iron Age Xiongnu Empire in 209 BC. Monuments of the pre-Xiongnu Bronze Age include deer stones, keregsur kurgans, square slab tombs, rock paintings. Although cultivation of crops has continued since the Neolithic, agriculture has always remained small in scale compared to pastoral nomadism. Agriculture arose independently in the region; the population during the Copper Age has been described as mongoloid in the east of what is now Mongolia, as europoid in the west.
Tocharians and Scythians inhabited western Mongolia during the Bronze Age. The mummy of a Scythian warrior, believed to be about 2,500 years old, was a 30- to 40-year-old man with blond hair; as equine nomadism was introduced into Mongolia, the political center of the Eurasian Steppe shifted to Mongolia, where it remained until the 18th century CE. The intrusions of northern pastoralists into China during the Shang dynasty and Zhou dynasty presaged the age of nomadic empires; the concept of Mongolia as an independent power north of China is expressed in a letter sent by Emperor Wen of Han to Laoshang Chanyu in 162 BC: Since prehistoric times, Mongolia has been inhabited by nomads who, from time to time, formed great confederations that rose to power and prominence. Common institutions were the office of the Khan, the Kurultai and right wings, imperial army and the decimal military system; the first of these empires, the Xiongnu of undetermined