The Eocene Epoch, lasting from 56 to 33.9 million years ago, is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch; the start of the Eocene is marked by a brief period in which the concentration of the carbon isotope 13C in the atmosphere was exceptionally low in comparison with the more common isotope 12C. The end is set at a major extinction event called the Grande Coupure or the Eocene–Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay; as with other geologic periods, the strata that define the start and end of the epoch are well identified, though their exact dates are uncertain. The name Eocene comes from the Ancient Greek ἠώς and καινός and refers to the "dawn" of modern fauna that appeared during the epoch; the Eocene epoch is conventionally divided into early and late subdivisions.
The corresponding rocks are referred to as lower and upper Eocene. The Ypresian stage constitutes the lower, the Priabonian stage the upper; the Eocene Epoch contained a wide variety of different climate conditions that includes the warmest climate in the Cenozoic Era and ends in an icehouse climate. The evolution of the Eocene climate began with warming after the end of the Palaeocene–Eocene Thermal Maximum at 56 million years ago to a maximum during the Eocene Optimum at around 49 million years ago. During this period of time, little to no ice was present on Earth with a smaller difference in temperature from the equator to the poles. Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene-Oligocene transition at 34 million years ago. During this decrease ice began to reappear at the poles, the Eocene-Oligocene transition is the period of time where the Antarctic ice sheet began to expand. Greenhouse gases, in particular carbon dioxide and methane, played a significant role during the Eocene in controlling the surface temperature.
The end of the PETM was met with a large sequestration of carbon dioxide in the form of methane clathrate and crude oil at the bottom of the Arctic Ocean, that reduced the atmospheric carbon dioxide. This event was similar in magnitude to the massive release of greenhouse gasses at the beginning of the PETM, it is hypothesized that the sequestration was due to organic carbon burial and weathering of silicates. For the early Eocene there is much discussion; this is due to numerous proxies representing different atmospheric carbon dioxide content. For example, diverse geochemical and paleontological proxies indicate that at the maximum of global warmth the atmospheric carbon dioxide values were at 700–900 ppm while other proxies such as pedogenic carbonate and marine boron isotopes indicate large changes of carbon dioxide of over 2,000 ppm over periods of time of less than 1 million years. Sources for this large influx of carbon dioxide could be attributed to volcanic out-gassing due to North Atlantic rifting or oxidation of methane stored in large reservoirs deposited from the PETM event in the sea floor or wetland environments.
For contrast, today the carbon dioxide levels are at 400 ppm or 0.04%. At about the beginning of the Eocene Epoch the amount of oxygen in the earth's atmosphere more or less doubled. During the early Eocene, methane was another greenhouse gas that had a drastic effect on the climate. In comparison to carbon dioxide, methane has much greater effect on temperature as methane is around 34 times more effective per molecule than carbon dioxide on a 100-year scale. Most of the methane released to the atmosphere during this period of time would have been from wetlands and forests; the atmospheric methane concentration today is 0.000179% or 1.79 ppmv. Due to the warmer climate and sea level rise associated with the early Eocene, more wetlands, more forests, more coal deposits would be available for methane release. Comparing the early Eocene production of methane to current levels of atmospheric methane, the early Eocene would be able to produce triple the amount of current methane production; the warm temperatures during the early Eocene could have increased methane production rates, methane, released into the atmosphere would in turn warm the troposphere, cool the stratosphere, produce water vapor and carbon dioxide through oxidation.
Biogenic production of methane produces carbon dioxide and water vapor along with the methane, as well as yielding infrared radiation. The breakdown of methane in an oxygen atmosphere produces carbon monoxide, water vapor and infrared radiation; the carbon monoxide is not stable so it becomes carbon dioxide and in doing so releases yet more infrared radiation. Water vapor traps more infrared than does carbon dioxide; the middle to late Eocene marks not only the switch from warming to cooling, but the change in carbon dioxide from increasing to decreasing. At the end of the Eocene Optimum, carbon dioxide began decreasing due to increased siliceous plankton productivity and marine carbon burial. At the beginning of the middle Eocene an event that may have triggered or helped with the draw down of carbon dioxide was the Azolla event at around 49 million years ago. With the equable climate during the early Eocene, warm temperatures in the arctic allowed for the growth of azolla, a floating aquatic fern, on the Arctic Ocean.
Compared to current carb
The Caspian Sea is the world's largest inland body of water, variously classed as the world's largest lake or a full-fledged sea. It is an endorheic basin located between Europe and Asia, to the east of the Caucasus Mountains and to the west of the broad steppe of Central Asia; the sea has a surface area of 371,000 km2 and a volume of 78,200 km3. It has a salinity of 1.2%, about a third of the salinity of most seawater. It is bounded by Kazakhstan to the northeast, Russia to the northwest, Azerbaijan to the west, Iran to the south, Turkmenistan to the southeast; the Caspian Sea is home to a wide range of species and may be best known for its caviar and oil industries. Pollution from the oil industry and dams on rivers draining into the Caspian Sea have had negative effects on the organisms living in the sea; the wide and endorheic Caspian Sea has a north–south orientation and its main freshwater inflow, the Volga River, enters at the shallow north end. Two deep basins occupy its southern areas.
These lead to horizontal differences in temperature and ecology. The Caspian Sea spreads out over nearly 750 miles from north to south, with an average width of 200 miles, it covers a region of around 149,200 square miles and its surface is about 90 feet below sea level. The sea bed in the southern part reaches as low as 1,023 m below sea level, the second lowest natural depression on Earth after Lake Baikal; the ancient inhabitants of its coast perceived the Caspian Sea as an ocean because of its saltiness and large size. The word Caspian is derived from the name of the Caspi, an ancient people who lived to the southwest of the sea in Transcaucasia. Strabo wrote that "to the country of the Albanians belongs the territory called Caspiane, named after the Caspian tribe, as was the sea. Moreover, the Caspian Gates, the name of a region in Iran's Tehran province indicates that they migrated to the south of the sea; the Iranian city of Qazvin shares the root of its name with that of the sea. In fact, the traditional Arabic name for the sea itself is Baḥr al-Qazwin.
In classical antiquity among Greeks and Persians it was called the Hyrcanian Ocean. In Persian middle age, as well as in modern Iran, it is known as Daryā-e Khazar. Ancient Arabic sources refer to it as Baḥr Gīlān meaning "the Gilan Sea". Turkic languages refer to the lake as Khazar Sea. In Turkmen, the name is Hazar deňizi, in Azeri, it is Xəzər dənizi, in modern Turkish, it is Hazar denizi. In all these cases, the second word means "sea", the first word refers to the historical Khazars who had a large empire based to the north of the Caspian Sea between the 7th and 10th centuries. An exception is Kazakh, where it is called Kaspiy teñizi. Renaissance European maps labelled it as Mar de Bachu, or Mar de Sala. Old Russian sources call it the Khvalis Sea after the name of Khwarezmia. In modern Russian, it is called Каспи́йское мо́ре, Kaspiyskoye more; the Caspian Sea, like the Black Sea, is a remnant of the ancient Paratethys Sea. Its seafloor is, therefore, a standard oceanic basalt and not a continental granite body.
It became landlocked about 5.5 million years ago due to a fall in sea level. During warm and dry climatic periods, the landlocked sea dried up, depositing evaporitic sediments like halite that were covered by wind-blown deposits and were sealed off as an evaporite sink when cool, wet climates refilled the basin. Due to the current inflow of fresh water in the north, the Caspian Sea water is fresh in its northern portions, getting more brackish toward the south, it is most saline on the Iranian shore. The mean salinity of the Caspian is one third that of Earth's oceans; the Garabogazköl embayment, which dried up when water flow from the main body of the Caspian was blocked in the 1980s but has since been restored exceeds oceanic salinity by a factor of 10. The Caspian Sea is the largest inland body of water in the world and accounts for 40 to 44% of the total lacustrine waters of the world; the coastlines of the Caspian are shared by Azerbaijan, Kazakhstan and Turkmenistan. The Caspian is divided into three distinct physical regions: the Northern and Southern Caspian.
The Northern–Middle boundary is the Mangyshlak Threshold, which runs through Chechen Island and Cape Tiub-Karagan. The Middle–Southern boundary is the Apsheron Threshold, a sill of tectonic origin between the Eurasian continent and an oceanic remnant, that runs through Zhiloi Island and Cape Kuuli; the Garabogazköl Bay is the saline eastern inlet of the Caspian, part of Turkmenistan and at times has been a lake in its own right due to the isthmus that cuts it off from the Caspian. Differences between the three regions are dramatic; the Northern Caspian only includes the Caspian shelf, is shallow. The sea noticeably drops off towards the Middle Caspian; the Southern Caspian is the deepest, with oceanic depths of over 1,000 metres exceeding the depth of other reg
Ostracods, or ostracodes, are a class of the Crustacea, sometimes known as seed shrimp. Some 70,000 species have been grouped into several orders, they are small crustaceans around 1 mm in size, but varying from 0.2 to 30 mm in the case of Gigantocypris. Their bodies are flattened from side to side and protected by a bivalve-like, chitinous or calcareous valve or "shell"; the hinge of the two valves is in the upper region of the body. Ostracods are grouped together based on gross morphology. While early work indicated the group may not be monophyletic. Many ostracods the Podocopida, are found in fresh water, terrestrial species of Mesocypris are known from humid forest soils of South Africa and New Zealand, they have a wide range of diets, the group includes carnivores, herbivores and filter feeders. As of 2008, around 2000 species and 200 genera of nonmarine ostracods are found. However, a large portion of diversity is still undescribed, indicated by undocumented diversity hotspots of temporary habitats in Africa and Australia.
Of the known specific and generic diversity of nonmarine ostracods, half belongs to one family, Cyprididae. Many Cyprididae occur in temporary water bodies and have drought-resistant eggs, mixed/parthenogenetic reproduction, the ability to swim; these biological attributes preadapt them to form successful radiations in these habitats. Ostracod comes from the Greek óstrakon meaning tile; the word "ostracize" comes from the same root due to the practice of voting with shells or potsherds. Ostracods are "by far the most common arthropods in the fossil record" with fossils being found from the early Ordovician to the present. An outline microfaunal zonal scheme based on both Foraminifera and Ostracoda was compiled by M. B. Hart. Freshwater ostracods have been found in Baltic amber of Eocene age, having been washed onto trees during floods. Ostracods have been useful for the biozonation of marine strata on a local or regional scale, they are invaluable indicators of paleoenvironments because of their widespread occurrence, small size preservable moulted, calcified bivalve carapaces.
A find in Queensland, Australia in 2013, announced in May 2014, at the Bicentennary Site in the Riversleigh World Heritage area, revealed both male and female specimens with well preserved soft tissue. This set the Guinness World Record for the oldest penis. Males had observable sperm, the oldest yet seen and, when analysed, showed internal structures and has been assessed as being the largest sperm of any animal recorded, it was assessed that the fossilisation was achieved within several days, due to phosphorus in the bat droppings of the cave where the ostracods were living. The body of an ostracod is encased by two valves. A distinction is made between the body with its appendages; the body consists of a thorax, separated by a slight constriction. Unlike many other crustaceans, the body is not divided into segments; the abdomen is regressed or absent, whereas the adult gonads are large. The head is the largest part of the body, bears most of the appendages. Two pairs of well-developed antennae are used to swim through the water.
In addition, there is two pairs of maxillae. The thorax has two pairs of appendages, but these are reduced to a single pair, or absent, in many species; the two "rami", or projections, from the tip of the tail, point downwards and forward from the rear of the shell. Ostracods have no gills, instead taking in oxygen through branchial plates on the body surface. Most ostracods have no heart or circulatory system, blood circulates between the valves of the shell. Nitrogenous waste is excreted through glands on antennae, or both; the primary sense of ostracods is touch, as they have several sensitive hairs on their bodies and appendages. However, they do possess a single naupliar eye, and, in some cases, a pair of compound eyes, as well. A new method is in development called mutual ostracod temperature range, similar to the mutual climatic range used for beetles, which can be used to infer palaeotemperatures; the ratio of oxygen-18 to oxygen-16 and the ratio of magnesium to calcium in the calcite of ostracod valves can be used to infer information about past hydrological regimes, global ice volume and water temperatures.
Male ostracods have corresponding to two genital openings on the female. The individual sperm are large, are coiled up within the testis prior to mating. Mating occurs during swarming, with large numbers of females swimming to join the males; some species are or wholly parthenogenetic. In most ostracods, eggs are either laid directly into the water as plankton, or are attached to vegetation or the substratum. However, in some species, the eggs are brooded inside the shell, giving them a greater degree of protection; the eggs hatch into nauplius larvae, which have a hard shell. A v
The Alps are the highest and most extensive mountain range system that lies in Europe, separating Southern from Central and Western Europe and stretching 1,200 kilometres across eight Alpine countries: France, Italy, Liechtenstein, Austria and Slovenia. The mountains were formed over tens of millions of years as the African and Eurasian tectonic plates collided. Extreme shortening caused by the event resulted in marine sedimentary rocks rising by thrusting and folding into high mountain peaks such as Mont Blanc and the Matterhorn. Mont Blanc spans the French–Italian border, at 4,810 m is the highest mountain in the Alps; the Alpine region area contains about a hundred peaks higher than 4,000 metres. The altitude and size of the range affects the climate in Europe. Wildlife such as ibex live in the higher peaks to elevations of 3,400 m, plants such as Edelweiss grow in rocky areas in lower elevations as well as in higher elevations. Evidence of human habitation in the Alps goes back to the Palaeolithic era.
A mummified man, determined to be 5,000 years old, was discovered on a glacier at the Austrian–Italian border in 1991. By the 6th century BC, the Celtic La Tène culture was well established. Hannibal famously crossed the Alps with a herd of elephants, the Romans had settlements in the region. In 1800, Napoleon crossed one of the mountain passes with an army of 40,000; the 18th and 19th centuries saw an influx of naturalists and artists, in particular, the Romantics, followed by the golden age of alpinism as mountaineers began to ascend the peaks. The Alpine region has a strong cultural identity; the traditional culture of farming and woodworking still exists in Alpine villages, although the tourist industry began to grow early in the 20th century and expanded after World War II to become the dominant industry by the end of the century. The Winter Olympic Games have been hosted in the Swiss, Italian and German Alps. At present, the region has 120 million annual visitors; the English word Alps derives from the Latin Alpes.
Maurus Servius Honoratus, an ancient commentator of Virgil, says in his commentary that all high mountains are called Alpes by Celts. The term may be common to Italo-Celtic, because the Celtic languages have terms for high mountains derived from alp; this may be consistent with the theory. According to the Oxford English Dictionary, the Latin Alpes might derive from a pre-Indo-European word *alb "hill". Albania, a name not native to the region known as the country of Albania, has been used as a name for a number of mountainous areas across Europe. In Roman times, "Albania" was a name for the eastern Caucasus, while in the English languages "Albania" was used as a name for Scotland, although it is more derived from the Latin albus, the color white; the Latin word Alpes could come from the adjective albus. In modern languages the term alp, albe or alpe refers to a grazing pastures in the alpine regions below the glaciers, not the peaks. An alp refers to a high mountain pasture where cows are taken to be grazed during the summer months and where hay barns can be found, the term "the Alps", referring to the mountains, is a misnomer.
The term for the mountain peaks varies by nation and language: words such as Horn, Kopf, Spitze and Berg are used in German speaking regions. The Alps are a crescent shaped geographic feature of central Europe that ranges in a 800 km arc from east to west and is 200 km in width; the mean height of the mountain peaks is 2.5 km. The range stretches from the Mediterranean Sea north above the Po basin, extending through France from Grenoble, stretching eastward through mid and southern Switzerland; the range continues onward toward Vienna and east to the Adriatic Sea and Slovenia. To the south it dips into northern Italy and to the north extends to the southern border of Bavaria in Germany. In areas like Chiasso and Allgäu, the demarcation between the mountain range and the flatlands are clear; the countries with the greatest alpine territory are Austria, Italy and Switzerland. The highest portion of the range is divided by the glacial trough of the Rhône valley, from Mont Blanc to the Matterhorn and Monte Rosa on the southern side, the Bernese Alps on the northern.
The peaks in the easterly portion of the range, in Austria and Slovenia, are smaller than those in the central and western portions. The variances in nomenclature in the region spanned by the Alps makes classification of the mountains and subregions difficult, but a general classification is that of the Eastern Alps and Western Alps with the divide between the two occurring in eastern Switzerland according to geologist Stefan Schmid, near the Splügen Pass; the highest peaks of the Western Alps and Eastern Alps are Mont Blanc, at 4,810 m and Piz Bernina at 4,049 metres. The second-highest major
A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, petrified wood, coal, DNA remnants; the totality of fossils is known as the fossil record. Paleontology is the study of fossils: their age, method of formation, evolutionary significance. Specimens are considered to be fossils if they are over 10,000 years old; the oldest fossils are around 3.48 billion years old to 4.1 billion years old. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils; the development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host. There are many processes that lead to fossilization, including permineralization and molds, authigenic mineralization and recrystallization, adpression and bioimmuration.
Fossils vary in size from one-micrometre bacteria to dinosaurs and trees, many meters long and weighing many tons. A fossil preserves only a portion of the deceased organism that portion, mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may consist of the marks left behind by the organism while it was alive, such as animal tracks or feces; these types of fossil are called trace ichnofossils, as opposed to body fossils. Some fossils are called chemofossils or biosignatures; the process of fossilization varies according to external conditions. Permineralization is a process of fossilization; the empty spaces within an organism become filled with mineral-rich groundwater. Minerals precipitate from the groundwater; this process can occur in small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce detailed fossils. For permineralization to occur, the organism must become covered by sediment soon after death, otherwise decay commences.
The degree to which the remains are decayed when covered determines the details of the fossil. Some fossils consist only of skeletal teeth; this is a form of diagenesis. In some cases, the original remains of the organism dissolve or are otherwise destroyed; the remaining organism-shaped hole in the rock is called an external mold. If this hole is filled with other minerals, it is a cast. An endocast, or internal mold, is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail or the hollow of a skull; this is a special form of mold formation. If the chemistry is right, the organism can act as a nucleus for the precipitation of minerals such as siderite, resulting in a nodule forming around it. If this happens before significant decay to the organic tissue fine three-dimensional morphological detail can be preserved. Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented examples of such mineralization.
Replacement occurs. In some cases mineral replacement of the original shell occurs so and at such fine scales that microstructural features are preserved despite the total loss of original material. A shell is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, as from aragonite to calcite. Compression fossils, such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism's tissues. In this case the fossil consists of original material, albeit in a geochemically altered state; this chemical change is an expression of diagenesis. What remains is a carbonaceous film known as a phytoleim, in which case the fossil is known as a compression. However, the phytoleim is lost and all that remains is an impression of the organism in the rock—an impression fossil. In many cases, however and impressions occur together. For instance, when the rock is broken open, the phytoleim will be attached to one part, whereas the counterpart will just be an impression.
For this reason, one term covers the two modes of preservation: adpression. Because of their antiquity, an unexpected exception to the alteration of an organism's tissues by chemical reduction of the complex organic molecules during fossilization has been the discovery of soft tissue in dinosaur fossils, including blood vessels, the isolation of proteins and evidence for DNA fragments. In 2014, Mary Schweitzer and her colleagues reported the presence of iron particles associated with soft tissues recovered from dinosaur fossils. Based on various experiments that studied the interaction of iron in haemoglobin with blood vessel tissue they proposed that solution hypoxia coupled with iron chelation enhances the stability and preservation of soft tissue and provides the basis for an explanation for the unforeseen preservation of fossil soft tissues. However, a older study based on eight taxa ranging in time from the Devonian to the Jurassic found that reasonably well-preserved fibrils that represent collagen were preser
A mountain chain is a row of high mountain summits, a linear sequence of interconnected or related mountains, or a contiguous ridge of mountains within a larger mountain range. The term is used for elongated fold mountains with several parallel chains. While in mountain ranges, the term mountain chain is common, in hill ranges a sequence of hills tends to be referred to a ridge or hill chain. Elongated mountain chains occur most in the orogeny of fold mountains, nappe belts. Other types of range such as horst ranges, fault block mountain or truncated uplands form parallel mountain chains. However, if a truncated upland is eroded into a high table land, the incision of valleys can lead to the formations of mountain or hill chains; the chain-like arrangement of summits and the formation of long, jagged mountain crests – known in Spanish as sierras – is a consequence of their collective formation by mountain building forces. The linear structure is linked to the direction of these thrust forces and the resulting mountain folding which in turn relates to the fault lines in the upper part of the earth's crust, that run between the individual mountain chains.
In these fault zones, the rock, which has sometimes been pulverised, is eroded, so that large river valleys are carved out. These, so called longitudinal valleys reinforce the trend, during the early mountain building phase, towards the formation of parallel chains of mountains; the tendency of fold mountains to produce parallel chains is due to their rock structure and the propulsive forces of plate tectonics. The uplifted rock masses are either magmatic plutonic rocks shaped because of their higher temperature, or sediments or metamorphic rocks, which have a less robust structure, that are deposited in the synclines; as a result of orogenic movements, strata of folded rock are formed that are crumpled out of their original horizontal plane and thrust against one another. The longitudinal stretching of the folds takes place at right angles to the direction of the lateral thrusting; the overthrust folds of a nappe belt are formed in a similar way. Although the fold mountains, chain mountains and nappe belts around the world were formed at different times in the earth's history, all during their initial mountain building phases, they are morphologically similar.
Harder rock forms continuous ridges that follow the strike of the beds and folds. The mountain chains or ridges therefore run parallel to one another, they are only interrupted by short narrow, transverse valleys, which form water gaps. During the course of earth history, erosion by water and wind carried away the highest points of the mountain crests and carved out individual summits or summit chains. Between them, notches were formed that, depending on altitude and rock-type, form knife-edged cols or gentler mountain passes and saddles. Nappe or fold mountains, with their parallel mountain chains have a common geological age, but may consist of various types of rock. For example, in the Central Alps, granitic rocks and metamorphic slate are found, while to the north and south, are the Limestone Alps; the Northern Limestone Alps are, followed by soft flysch mountains and the molasse zone. The type of rock influences the appearance of the mountain ranges markedly, because erosion leads to different topography depending on the hardness of the rock and its petrological structure.
In addition to height and climate, other factors are the layering of the rock, its gradient and aspect, the types of waterbody and the lines of dislocation. For hard rock massifs, rugged rock faces and mighty scree slopes are typical. By contrast, flysch or slate forms gentler mountain shapes and kuppen or domed mountaintops, because the rock is not porous, but shaped. Orogeny Tectonics List of highest mountains on earth Wissen heute: Geologie. Kaiser-Verlag, Florence/Klagenfurt, 1995 Der geologische Aufbau Österreichs. Geologische Bundesanstalt, Springer-Verlag Vienna/ New York PanGeo, Erdwissenschaften in Österreich. Conference proceedings, 200 pp. Sessions on the Neogene, TRANSALP I and II. Univ. Salzburg, 2005 Fischer-Lexikon Geographie, pp. 101–129, Frankfurt, 1959 Großer Weltatlas, Enzyklopädischer Teil. Publ. ÖAMTC, Vienna, ~1980 André Cailleux: Der unbekannte Planet: Anatomie der Erde. Kindlers Universitätsbibliothek, Munich, 1968, Chapters 1 and 3 Gebirge, in: Lueger, Otto: Lexikon der gesamten Technik und ihrer Hilfswissenschaften, Vol. 4 Stuttgart, Leipzig, 1906, pp. 316-317
Gondwana, was a supercontinent that existed from the Neoproterozoic until the Jurassic. It was formed by the accretion of several cratons. Gondwana became the largest piece of continental crust of the Paleozoic Era, covering an area of about 100,000,000 km2. During the Carboniferous Period, it merged with Laurussia to form a larger supercontinent called Pangaea. Gondwana broke up during the Mesozoic Era; the remnants of Gondwana make up about two thirds of today's continental area, including South America, Antarctica and the Indian Subcontinent. The formation of Gondwana began c. 800 to 650 Ma with the East African Orogeny, the collision of India and Madagascar with East Africa,and was completed c. 600 to 530 Ma with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa and the addition of Australia and Antarctica, respectively. The continent of Gondwana was named by Austrian scientist Eduard Suess, after the Gondwana region of central India, derived from Sanskrit for "forest of the Gonds".
The name had been used in a geological context, first by H. B. Medlicott in 1872, from which the Gondwana sedimentary sequences are described; the term "Gondwanaland" is preferred by some scientists in order to make a clear distinction between the region and the supercontinent. The assembly of Gondwana was a protracted process during the Neoproterozoic and Paleozoic, which however remains incompletely understood because of the lack of paleo-magnetic data. Several orogenies, collectively known as the Pan-African orogeny, led to the amalgamation of most of the continental fragments of a much older supercontinent, Rodinia. One of those orogenic belts, the Mozambique Belt, formed 800 to 650 Ma and was interpreted as the suture between East and West Gondwana. Three orogenies were recognized during the 1990s: the East African Orogeny and Kuunga orogeny, the collision between East Gondwana and East Africa in two steps, the Brasiliano orogeny, the successive collision between South American and African cratons.
The final stages of Gondwanan assembly overlapped with the opening of the Iapetus Ocean between Laurentia and western Gondwana. During this interval, the Cambrian explosion occurred. Laurentia was docked against the western shores of a united Gondwana for a short period near the Precambrian/Cambrian boundary, forming the short-lived and still disputed supercontinent Pannotia; the Mozambique Ocean separated the Congo–Tanzania–Bangweulu Block of central Africa from Neoproterozoic India. The Azania continent was an island in the Mozambique Ocean; the Australia/Mawson continent was still separated from India, eastern Africa, Kalahari by c. 600 Ma, when most of western Gondwana had been amalgamated. By c. 550 Ma, India had reached its Gondwanan position. Meanwhile, on the other side of the newly-forming Africa, Kalahari collided with Congo and Rio de la Plata which closed the Adamastor Ocean. C. 540–530 Ma, the closure of the Mozambique Ocean brought India next to Australia–East Antarctica, both North and South China were located in proximity to Australia.
As the rest of Gondwana formed, a complex series of orogenic events assembled the eastern parts of Gondwana c. 750 to 530 Ma. First the Arabian-Nubian Shield collided with eastern Africa in the East African Orogeny c.750 to 620 Ma. Australia and East Antarctica were merged with the remaining Gondwana c. 570 to 530 Ma in the Kuunga Orogeny. The Malagasy orogeny at about 550–515 Mya affected Madagascar, eastern East Africa and southern India. In it, Neoproterozoic India collided with the combined Azania and Congo–Tanzania–Bangweulu Block, suturing along the Mozambique Belt; the 18,000 km -long Terra Australis Orogen developed along Gondwana's western and eastern margins. Proto-Gondwanan Cambrian arc belts from this margin have been found in eastern Australia, New Zealand, Antarctica. Though these belts formed a continuous arc chain, the direction of subduction was different between the Australian-Tasmanian and New Zealand-Antarctica arc segments. A large number of terranes were accreted to Eurasia during Gondwana's existence but the Cambrian or Precambrian origin of many of these terranes remains uncertain.
For example, some Palaeozoic terranes and microcontinents that now make up Central Asia called the "Kazakh" and "Mongolian terranes", were progressively amalgamated into the continent Kazakhstania in the Late Silurian. Whether these blocks originated on the shores of Gondwana is not known. In the Early Palaeozoic the Armorican terrane, which today form large parts of France, was part of either Peri-Gondwana or core Gondwana. Precambrian rocks from the Iberian Peninsula suggest it too formed part of core Gondwana before its detachment as an orocline in the Variscan orogeny close to the Carboniferous–Permian boundary. South-east Asia is made of Gondwanan and Cathaysian continental fragments that were assembled during the Mid-Palaeozoic and Cenozoic; this p