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93-526: McGraths Flat is an Australian research site containing fossils and other evidence of animals and plants that existed in Miocene Australia. Located in central New South Wales, specimens at the site are in an exceptional state of preservation, described in paleontology as a Konservat-Lagerstätten , deposited in unusual conditions that record microscopic details of soft tissues and delicate structures. Fossil evidence of animals with soft bodies, unlike

186-542: A broader aridification trend. The EMCI ended 18 million years ago, giving way to the Middle Miocene Warm Interval (MMWI), the warmest part of which was the MMCO that began 16 million years ago. As the world transitioned into the MMCO, carbon dioxide concentrations varied between 300 and 500 ppm. Global annual mean surface temperature during the MMCO was about 18.4 °C. MMCO warmth was driven by

279-409: A chapter on continental drift, proposing that Earth's mantle contained convection cells which dissipated radioactive heat and moved the crust at the surface. Holmes's proposal resolved the phase disequilibrium objection (the underlying fluid was kept from solidifying by radioactive heating from the core). However, scientific communication in the 1930s and 1940s was inhibited by World War II , and

372-529: A clade of large terrestrial predatory crocodyliformes distantly related to modern crocodilians, from which they likely diverged over 180 million years ago, are known from the Miocene of South America. The last Desmostylians thrived during this period before becoming the only extinct marine mammal order. The pinnipeds , which appeared near the end of the Oligocene, became more aquatic. A prominent genus

465-570: A cooler, drier climate. C 4 grasses, which are able to assimilate carbon dioxide and water more efficiently than C 3 grasses, expanded to become ecologically significant near the end of the Miocene between 6 and 7 million years ago, although they did not expand northward during the Late Miocene. The expansion of grasslands and radiations among terrestrial herbivores correlates to fluctuations in CO 2 . One study, however, has attributed

558-675: A freshwater reptile rather like a small crocodile, found both in Brazil and South Africa , are one example; another is the discovery of fossils of the land reptile Lystrosaurus in rocks of the same age at locations in Africa , India , and Antarctica . There is also living evidence, with the same animals being found on two continents. Some earthworm families (such as Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa. The complementary arrangement of

651-486: A good analogue for future warmer climates caused by anthropogenic global warming , with this being especially true of the global climate during the Middle Miocene Climatic Optimum (MMCO), because the last time carbon dioxide levels were comparable to projected future atmospheric carbon dioxide levels resulting from anthropogenic climate change was during the MMCO. The Ross Sea margin of

744-435: A good model for a "living fossil". Eucalyptus fossil leaves occur in the Miocene of New Zealand , where the genus is not native today, but have been introduced from Australia . Both marine and continental fauna were fairly modern, although marine mammals were less numerous. Only in isolated South America and Australia did widely divergent fauna exist. In Eurasia, genus richness shifted southward to lower latitudes from

837-598: A major expansion of Antarctic glaciers. This severed the connection between the Indian Ocean and the Mediterranean Sea and formed the present land connection between Afro-Arabia and Eurasia. The subsequent uplift of mountains in the western Mediterranean region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea (known as the Messinian salinity crisis ) near

930-480: A major expansion of grass-grazer ecosystems . Herds of large, swift grazers were hunted by predators across broad sweeps of open grasslands , displacing desert, woodland, and browsers . The higher organic content and water retention of the deeper and richer grassland soils , with long-term burial of carbon in sediments, produced a carbon and water vapor sink. This, combined with higher surface albedo and lower evapotranspiration of grassland, contributed to

1023-589: A map of the world and considers carefully the coasts of the three [continents]." In 1889, Alfred Russel Wallace remarked, "It was formerly a very general belief, even amongst geologists, that the great features of the earth's surface, no less than the smaller ones, were subject to continual mutations, and that during the course of known geological time the continents and great oceans had, again and again, changed places with each other." He quotes Charles Lyell as saying, "Continents, therefore, although permanent for whole geological epochs, shift their positions entirely in

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1116-409: A minority of scientific proponents over the decades, the theory of continental drift was largely rejected for many years, with evidence in its favor considered insufficient. One problem was that a plausible driving force was missing. A second problem was that Wegener's estimate of the speed of continental motion, 250 cm/year (100 in/year), was implausibly high. (The currently accepted rate for

1209-482: A now-discredited Expanding Earth theory . Continental drift without expansion was proposed by Frank Bursley Taylor , who suggested in 1908 (published in 1910) that the continents were moved into their present positions by a process of "continental creep", later proposing a mechanism of increased tidal forces during the Cretaceous dragging the crust towards the equator. He was the first to realize that one of

1302-544: A permanent feature of the Earth's surface, rather than them having "changed places" with the continents. Eduard Suess had proposed a supercontinent Gondwana in 1885 and the Tethys Ocean in 1893, assuming a land-bridge between the present continents submerged in the form of a geosyncline , and John Perry had written an 1895 paper proposing that the Earth's interior was fluid, and disagreeing with Lord Kelvin on

1395-602: A significant drop in atmospheric carbon dioxide levels. Both continental and oceanic thermal gradients in mid-latitudes during the Early Miocene were very similar to those in the present. Global cooling caused the East Asian Summer Monsoon (EASM) to begin to take on its modern form during the Early Miocene. From 22.1 to 19.7 Ma, the Xining Basin experienced relative warmth and humidity amidst

1488-700: A significant local decline along the northeastern coast of Australia during the Tortonian, most likely due to warming seawater. Cetaceans attained their greatest diversity during the Miocene, with over 20 recognized genera of baleen whales in comparison to only six living genera. This diversification correlates with emergence of gigantic macro-predators such as megatoothed sharks and raptorial sperm whales . Prominent examples are O. megalodon and L. melvillei . Other notable large sharks were O. chubutensis , Isurus hastalis , and Hemipristis serra . Crocodilians also showed signs of diversification during

1581-651: A zone of low rainfall in the Late Miocene. The Indian Plate continued to collide with the Eurasian Plate , creating new mountain ranges and uplifting the Tibetan Plateau , resulting in the rain shadowing and aridification of the Asian interior. The Tian Shan experienced significant uplift in the Late Miocene, blocking westerlies from coming into the Tarim Basin and drying it as a result. At

1674-423: Is created at spreading centers , and this, along with subduction , drives the system of plates in a chaotic manner, resulting in continuous orogeny and areas of isostatic imbalance. Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around the shores of different continents, suggesting that they were once joined. The fossils of Mesosaurus ,

1767-663: The Mid-Atlantic Ridge , arguing with this that the floor of the Atlantic Ocean was undergoing extension just like Reykjanes. Bernauer thought this extension had drifted the continents only 100–200 km (60–120 mi) apart, the approximate width of the volcanic zone in Iceland . David Attenborough , who attended university in the second half of the 1940s, recounted an incident illustrating its lack of acceptance then: "I once asked one of my lecturers why he

1860-559: The Middle Miocene Climate Transition (MMCT). Abrupt increases in opal deposition indicate this cooling was driven by enhanced drawdown of carbon dioxide via silicate weathering. The MMCT caused a sea surface temperature (SST) drop of approximately 6 °C in the North Atlantic. The drop in benthic foraminiferal δ O values was most noticeable in the waters around Antarctica, suggesting cooling

1953-560: The carbon cycle occurred approximately 6 Ma, causing continental carbon reservoirs to no longer expand during cold spells, as they had done during cold periods in the Oligocene and most of the Miocene. At the end of the Miocene, global temperatures rose again as the amplitude of Earth's obliquity increased, which caused increased aridity in Central Asia. Around 5.5 Ma, the EAWM underwent a period of rapid intensification. Life during

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2046-593: The geology of the Himalaya occurred during that epoch, affecting monsoonal patterns in Asia, which were interlinked with glacial periods in the northern hemisphere. The Miocene faunal stages from youngest to oldest are typically named according to the International Commission on Stratigraphy : Regionally, other systems are used, based on characteristic land mammals; some of them overlap with

2139-534: The " Zanclean flood ". Also during the early Miocene (specifically the Aquitanian and Burdigalian Stages), the apes first evolved, began diversifying, and became widespread throughout the Old World . Around the end of this epoch, the ancestors of humans had split away from the ancestors of the chimpanzees and had begun following their own evolutionary path during the final Messinian Stage (7.5–5.3 Ma) of

2232-562: The 1930s to the late 1950s, works by Vening-Meinesz , Holmes, Umbgrove , and numerous others outlined concepts that were close or nearly identical to modern plate tectonics theory. In particular, the English geologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the sea , and in 1928 that convection currents within the mantle might be the driving force. Holmes's views were particularly influential: in his bestselling textbook, Principles of Physical Geology, he included

2325-676: The Asian continent in the Permian period, but failing to account for glaciation in India, Australia and South Africa. Hans Stille and Leopold Kober opposed the idea of continental drift and worked on a "fixist" geosyncline model with Earth contraction playing a key role in the formation of orogens . Other geologists who opposed continental drift were Bailey Willis , Charles Schuchert , Rollin Chamberlin, Walther Bucher and Walther Penck . In 1939 an international geological conference

2418-710: The Central Paratethys, cut off from sources of freshwater input by its separation from the Eastern Paratethys. From 13.36 to 12.65 Ma, the Central Paratethys was characterised by open marine conditions, before the reopening of the Bârlad Strait resulted in a shift to brackish-marine conditions in the Central Paratethys, causing the Badenian-Sarmatian Extinction Event. As a result of the Bârlad Strait's reopening,

2511-837: The Early to the Middle Miocene. Europe's large mammal diversity significantly declined during the Late Miocene. In the Early Miocene, several Oligocene groups were still diverse, including nimravids , entelodonts , and three-toed equids. As in the previous Oligocene Epoch, oreodonts were still diverse, only to disappear in the earliest Pliocene. During the later Miocene mammals were more modern, with easily recognizable canids , bears , red pandas , procyonids , equids , beavers , deer , camelids , and whales , along with now-extinct groups like borophagine canids , certain gomphotheres , three-toed horses , and hornless rhinos like Teleoceras and Aphelos . The late Miocene also marks

2604-465: The Earth's mantle contained convection cells which dissipated heat produced by radioactive decay and moved the crust at the surface. His Principles of Physical Geology , ending with a chapter on continental drift, was published in 1944. Geological maps of the time showed huge land bridges spanning the Atlantic and Indian oceans to account for the similarities of fauna and flora and the divisions of

2697-720: The East Antarctic Ice Sheet (EAIS) was highly dynamic during the Early Miocene. The Miocene began with the Early Miocene Cool Event (Mi-1) around 23 million years ago, which marked the start of the Early Miocene Cool Interval (EMCI). This cool event occurred immediately after the Oligocene-Miocene Transition (OMT) during a major expansion of Antarctica's ice sheets, but was not associated with

2790-601: The East Asian Winter Monsoon (EAWM) became stronger synchronously with a southward shift of the subarctic front. Greenland may have begun to have large glaciers as early as 8 to 7 Ma, although the climate for the most part remained warm enough to support forests there well into the Pliocene. Zhejiang, China was noticeably more humid than today. In the Great Rift Valley of Kenya , there

2883-545: The German Geological Society on 6 January 1912. He proposed that the continents had once formed a single landmass, called Pangaea , before breaking apart and drifting to their present locations. Wegener was the first to use the phrase "continental drift" (1912, 1915) ( German : "die Verschiebung der Kontinente" ) and to publish the hypothesis that the continents had somehow "drifted" apart. Although he presented much evidence for continental drift, he

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2976-460: The LMC; extratropical sea surface temperatures dropped substantially by approximately 7–9 °C. 41 kyr obliquity cycles became the dominant orbital climatic control 7.7 Ma and this dominance strengthened 6.4 Ma. Benthic δ O values show significant glaciation occurred from 6.26 to 5.50 Ma, during which glacial-interglacial cycles were governed by the 41 kyr obliquity cycle. A major reorganisation of

3069-579: The Late Cretaceous, are known from the Miocene of Patagonia, represented by the mole-like Necrolestes . The youngest known representatives of metatherians (the broader grouping to which marsupials belong) in Europe, Asia and Africa are known from the Miocene, including the European herpetotheriid Amphiperatherium , the peradectids Siamoperadectes and Sinoperadectes from Asia, and

3162-653: The Late Miocene, the Earth's climate began to display a high degree of similarity to that of the present day . The 173 kyr obliquity modulation cycle governed by Earth's interactions with Saturn became detectable in the Late Miocene. By 12 Ma, Oregon was a savanna akin to that of the western margins of the Sierra Nevada of northern California . Central Australia became progressively drier, although southwestern Australia experienced significant wettening from around 12 to 8 Ma. The South Asian Winter Monsoon (SAWM) underwent strengthening ~9.2–8.5 Ma. From 7.9 to 5.8 Ma,

3255-574: The Miocene Epoch was mostly supported by the two newly formed biomes , kelp forests and grasslands . Grasslands allow for more grazers, such as horses , rhinoceroses , and hippos . Ninety-five percent of modern plants existed by the end of this epoch . Modern bony fish genera were established. A modern-style latitudinal biodiversity gradient appeared ~15 Ma. The coevolution of gritty , fibrous, fire-tolerant grasses and long-legged gregarious ungulates with high-crowned teeth , led to

3348-484: The Miocene. As in the Oligocene before it, grasslands continued to expand, and forests to dwindle. In the seas of the Miocene, kelp forests made their first appearance and soon became one of Earth's most productive ecosystems. The plants and animals of the Miocene were recognizably modern. Mammals and birds were well established. Whales , pinnipeds , and kelp spread. The Miocene is of particular interest to geologists and palaeoclimatologists because major phases of

3441-449: The Miocene. The largest form among them was a gigantic caiman Purussaurus which inhabited South America. Another gigantic form was a false gharial Rhamphosuchus , which inhabited modern age India . A strange form, Mourasuchus also thrived alongside Purussaurus . This species developed a specialized filter-feeding mechanism, and it likely preyed upon small fauna despite its gigantic size. The youngest members of Sebecidae ,

3534-555: The New Global Tectonics", published in 1968, using data collected from seismologic stations, including those he set up in the South Pacific. The modern theory of plate tectonics , refining Wegener, explains that there are two kinds of crust of different composition: continental crust and oceanic crust , both floating above a much deeper " plastic " mantle. Continental crust is inherently lighter. Oceanic crust

3627-550: The North American Great Plains and in Argentina . The global trend was towards increasing aridity caused primarily by global cooling reducing the ability of the atmosphere to absorb moisture, particularly after 7 to 8 million years ago. Uplift of East Africa in the late Miocene was partly responsible for the shrinking of tropical rain forests in that region, and Australia got drier as it entered

3720-656: The Oligocene–Miocene transgression. As the southern Andes rose in the Middle Miocene (14–12 million years ago) the resulting rain shadow originated the Patagonian Desert to the east. Far northern Australia was monsoonal during the Miocene. Although northern Australia is often believed to have been much wetter during the Miocene, this interpretation may be an artefact of preservation bias of riparian and lacustrine plants; this finding has itself been challenged by other papers. Western Australia, like today,

3813-502: The Pliocene, the climate slowly cooled towards a series of ice ages . The Miocene boundaries are not marked by distinct global events but by regionally defined transitions from the warmer Oligocene to the cooler Pliocene Epoch. During the Early Miocene, Afro-Arabia collided with Eurasia, severing the connection between the Mediterranean and Indian Oceans, and allowing the interchange of fauna between Eurasia and Africa, including

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3906-617: The Qiongdongnan Basin in the northern South China Sea indicates the Pearl River was a major source of sediment flux into the sea during the Early Miocene and was a major fluvial system as in the present. During the Oligocene and Early Miocene, the coast of northern Brazil, Colombia, south-central Peru , central Chile and large swathes of inland Patagonia were subject to a marine transgression . The transgressions in

3999-497: The activity of the Columbia River Basalts and enhanced by decreased albedo from the reduction of deserts and expansion of forests. Climate modelling suggests additional, currently unknown, factors also worked to create the warm conditions of the MMCO. The MMCO saw the expansion of the tropical climatic zone to much larger than its current size. The July ITCZ, the zone of maximal monsoonal rainfall, moved to

4092-421: The adjoining stripes reversed polarity. The best explanation was the "conveyor belt" or Vine–Matthews–Morley hypothesis . New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. The new crust is magnetized by the Earth's magnetic field, which undergoes occasional reversals . Formation of new crust then displaces

4185-826: The age of the Earth. Apart from the earlier speculations mentioned above, the idea that the American continents had once formed a single landmass with Eurasia and Africa was postulated by several scientists before Alfred Wegener 's 1912 paper. Although Wegener's theory was formed independently and was more complete than those of his predecessors, Wegener later credited a number of past authors with similar ideas: Franklin Coxworthy (between 1848 and 1890), Roberto Mantovani (between 1889 and 1909), William Henry Pickering (1907) and Frank Bursley Taylor (1908). The similarity of southern continent geological formations had led Roberto Mantovani to conjecture in 1889 and 1909 that all

4278-472: The aridity of the former. Unequivocally-recognizable dabbling ducks , plovers , typical owls , cockatoos and crows appear during the Miocene. By the epoch's end, all or almost all modern bird groups are believed to have been present; the few post-Miocene bird fossils which cannot be placed in the evolutionary tree with full confidence are simply too badly preserved, rather than too equivocal in character. Marine birds reached their highest diversity ever in

4371-638: The beginning of the Miocene, the northern margin of the Arabian plate, then part of the African landmass, collided with Eurasia; as a result, the Tethys seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish – Arabian region. The first step of this closure occurred 20 Ma, reducing water mass exchange by 90%, while the second step occurred around 13.8 Ma, coincident with

4464-577: The bones of mammals and reptiles, is rare in Australia, and discoveries at McGraths' Flat have revealed unknown species of invertebrates such as insects and spiders. The site, named for its discoverer, occurs on private land near the town of Gulgong . The degree of preservation at this Lagerstätte has been compared to the quality of that found at Crato Formation , Lake Eckfeld , and Libros . Other fossil sites in Australia, such as Riversleigh World Heritage Area , Bullock Creek and Alcoota , are rich in

4557-549: The continent of North America had its surface near tide-level, part above and part below it (p.196); and this will probably be proved to be the condition in Primordial time of the other continents also. And, if the outlines of the continents were marked out, it follows that the outlines of the oceans were no less so". Dana was enormously influential in America—his Manual of Mineralogy is still in print in revised form—and

4650-434: The continents had once been joined into a supercontinent ; Wegener noted the similarity of Mantovani's and his own maps of the former positions of the southern continents. In Mantovani's conjecture, this continent broke due to volcanic activity caused by thermal expansion , and the new continents drifted away from each other because of further expansion of the rip-zones, where the oceans now lie. This led Mantovani to propose

4743-540: The course of ages." and claims that the first to throw doubt on this was James Dwight Dana in 1849. In his Manual of Geology (1863), Dana wrote, "The continents and oceans had their general outline or form defined in earliest time. This has been proved with regard to North America from the position and distribution of the first beds of the Lower Silurian , – those of the Potsdam epoch . The facts indicate that

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4836-577: The course of this epoch . The youngest representatives of Choristodera , an extinct order of aquatic reptiles that first appeared in the Middle Jurassic , are known from the Miocene of Europe, belonging to the genus Lazarussuchus , which had been the only known surviving genus of the group since the beginning of the Eocene. The last known representatives of the archaic primitive mammal order Meridiolestida , which dominated South America during

4929-523: The dispersal of proboscideans and hominoids into Eurasia. During the late Miocene, the connections between the Atlantic and Mediterranean closed, causing the Mediterranean Sea to almost completely evaporate. This event is referred to as the " Messinian salinity crisis ". Then, at the Miocene–Pliocene boundary, the Strait of Gibraltar opened, and the Mediterranean refilled. That event is referred to as

5022-440: The early 20th century, that Earth's continents move or drift relative to each other over geologic time. The theory of continental drift has since been validated and incorporated into the science of plate tectonics , which studies the movement of the continents as they ride on plates of the Earth's lithosphere . The speculation that continents might have "drifted" was first put forward by Abraham Ortelius in 1596. A pioneer of

5115-553: The early to mid Miocene (23–15 Ma). Oceans cooled partly due to the formation of the Antarctic Circumpolar Current , and about 15 million years ago the ice cap in the southern hemisphere started to grow to its present form. The Greenland ice cap developed later, in the Middle Pliocene time, about 3 million years ago. Continental drift Continental drift is the theory , originating in

5208-548: The effects of continental motion would be the formation of mountains, attributing the formation of the Himalayas to the collision between the Indian subcontinent with Asia. Wegener said that of all those theories, Taylor's had the most similarities to his own. For a time in the mid-20th century, the theory of continental drift was referred to as the "Taylor-Wegener hypothesis". Alfred Wegener first presented his hypothesis to

5301-578: The end of the Miocene due to increased habitat uniformity. The expansion of grasslands in North America also led to an explosive radiation among snakes. Previously, snakes were a minor component of the North American fauna, but during the Miocene, the number of species and their prevalence increased dramatically with the first appearances of vipers and elapids in North America and the significant diversification of Colubridae (including

5394-422: The end of the Miocene. The Paratethys underwent a significant transgression during the early Middle Miocene. Around 13.8 Ma, during a global sea level drop, the Eastern Paratethys was cut off from the global ocean by the closure of the Bârlad Strait, effectively turning it into a saltwater lake. From 13.8 to 13.36 Ma, an evaporite period similar to the later Messinian salinity crisis in the Mediterranean ensued in

5487-637: The enigmatic Saint Bathans Mammal . Microbial life in the igneous crust of the Fennoscandian Shield shifted from being dominated by methanogens to being primarily composed of sulphate-reducing prokaryotes . The change resulted from fracture reactivation during the Pyrenean-Alpine orogeny, enabling sulphate-reducing microbes to permeate into the Fennoscandian Shield via descending surficial waters. Diatom diversity

5580-461: The evolution of both groups into modern representatives. The early Miocene Saint Bathans Fauna is the only Cenozoic terrestrial fossil record of the landmass, showcasing a wide variety of not only bird species, including early representatives of clades such as moa , kiwi and adzebills , but also a diverse herpetofauna of sphenodontians , crocodiles and turtles as well as a rich terrestrial mammal fauna composed of various species of bats and

5673-499: The expansion of grasslands not to a CO 2 drop but to the increasing seasonality and aridity, coupled with a monsoon climate, which made wildfires highly prevalent compared to before. The Late Miocene expansion of grasslands had cascading effects on the global carbon cycle, evidenced by the imprint it left in carbon isotope records. Cycads between 11.5 and 5 million years ago began to rediversify after previous declines in variety due to climatic changes, and thus modern cycads are not

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5766-718: The extinction of the last-surviving members of the hyaenodonts . Islands began to form between South and North America in the Late Miocene, allowing ground sloths like Thinobadistes to island-hop to North America. The expansion of silica-rich C 4 grasses led to worldwide extinctions of herbivorous species without high-crowned teeth . Mustelids diversified into their largest forms as terrestrial predators like Ekorus , Eomellivora , and Megalictis and bunodont otters like Enhydriodon and Sivaonyx appeared. Eulipotyphlans were widespread in Europe, being less diverse in Southern Europe than farther north due to

5859-542: The facing sides of South America and Africa is an obvious and temporary coincidence. In millions of years, slab pull , ridge-push , and other forces of tectonophysics will further separate and rotate those two continents. It was that temporary feature that inspired Wegener to study what he defined as continental drift although he did not live to see his hypothesis generally accepted. The widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia

5952-629: The findings of marine invertebrate fossils of both Atlantic and Pacific affinity in La Cascada Formation . Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography . The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene, forming the Chile Triple Junction . At first the Antarctic Plate subducted only in

6045-411: The human lineage) appeared in Africa at the very end of the Miocene, including Sahelanthropus , Orrorin , and an early form of Ardipithecus ( A. kadabba ). The chimpanzee–human divergence is thought to have occurred at this time. The evolution of bipedalism in apes at the end of the Miocene instigated an increased rate of faunal turnover in Africa. In contrast, European apes met their end at

6138-422: The lake levels of the Eastern Paratethys dropped as it once again became a sea. The Fram Strait opened during the Miocene and acted as the only throughflow for Atlantic Water into the Arctic Ocean until the Quaternary period. Due to regional uplift of the continental shelf, this water could not move through the Barents Seaway in the Miocene. The modern day Mekong Delta took shape after 8 Ma. Geochemistry of

6231-524: The magnetized crust apart, akin to a conveyor belt – hence the name. Without workable alternatives to explain the stripes, geophysicists were forced to conclude that Holmes had been right: ocean rifts were sites of perpetual orogeny at the boundaries of convection cells. By 1967, barely two decades after discovery of the mid-oceanic rifts, and a decade after discovery of the striping, plate tectonics had become axiomatic to modern geophysics. In addition, Marie Tharp , in collaboration with Bruce Heezen , who

6324-613: The modern view of mobilism was the Austrian geologist Otto Ampferer . The concept was independently and more fully developed by Alfred Wegener in his 1915 publication, "The Origin of Continents and Oceans". However, at that time his hypothesis was rejected by many for lack of any motive mechanism. In 1931, the English geologist Arthur Holmes proposed mantle convection for that mechanism. Abraham Ortelius ( Ortelius 1596 ), Theodor Christoph Lilienthal (1756), Alexander von Humboldt (1801 and 1845), Antonio Snider-Pellegrini ( Snider-Pellegrini 1858 ), and others had noted earlier that

6417-496: The north, increasing precipitation over southern China whilst simultaneously decreasing it over Indochina during the EASM. Western Australia was at this time characterised by exceptional aridity. In Antarctica, average summer temperatures on land reached 10 °C. In the oceans, the lysocline shoaled by approximately half of a kilometre during warm phases that corresponded to orbital eccentricity maxima. The MMCO ended around 14 million years ago, when global temperatures fell in

6510-478: The ocean floor using devices developed during World War II to detect submarines. Over the next decade, it became increasingly clear that the magnetization patterns were not anomalies, as had been originally supposed. In a series of papers published between 1959 and 1963, Heezen, Dietz, Hess, Mason, Vine, Matthews, and Morley collectively realized that the magnetization of the ocean floor formed extensive, zebra-like patterns: one stripe would exhibit normal polarity and

6603-560: The organizer of the conference, was also a fixist who together with Troll held the view that excepting the Pacific Ocean continents were not radically different from oceans in their behaviour. The mobilist theory of Émile Argand for the Alpine orogeny was criticized by Kurt Leuchs. The few drifters and mobilists at the conference appealed to biogeography (Kirsch, Wittmann), paleoclimatology ( Wegener, K ), paleontology (Gerth) and geodetic measurements (Wegener, K). F. Bernauer correctly equated Reykjanes in south-west Iceland with

6696-523: The origin of many modern genera such as Nerodia , Lampropeltis , Pituophis and Pantherophis ). Arthropods were abundant, including in areas such as Tibet where they have traditionally been thought to be undiverse. Neoisopterans diversified and expanded into areas they previously were absent from, such as Madagascar and Australia. In the oceans, brown algae , called kelp , proliferated, supporting new species of sea life, including otters , fish and various invertebrates . Corals suffered

6789-463: The possible herpetotheriid Morotodon from the late Early Miocene of Uganda. Approximately 100 species of apes lived during this time , ranging throughout Africa, Asia and Europe and varying widely in size, diet, and anatomy. Due to scanty fossil evidence it is unclear which ape or apes contributed to the modern hominid clade, but molecular evidence indicates this ape lived between 18 and 13 million years ago. The first hominins ( bipedal apes of

6882-846: The preceding Oligocene and following Pliocene Epochs: Continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South America and North America was absent, although South America was approaching the western subduction zone in the Pacific Ocean , causing both the rise of the Andes and a southward extension of the Meso-American peninsula. Mountain building took place in western North America , Europe , and East Asia . Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in

6975-421: The seabed beneath the sediments was chemically and physically different from continental crust. As oceanographers continued to bathymeter the ocean basins, a system of mid-oceanic ridges was detected. An important conclusion was that along this system, new ocean floor was being created, which led to the concept of the " Great Global Rift ". Meanwhile, scientists began recognizing odd magnetic variations across

7068-471: The separation of the Americas from Europe and Africa is about 2.5 cm/year (1 in/year).) Furthermore, Wegener was treated less seriously because he was not a geologist. Even today, the details of the forces propelling the plates are poorly understood. The English geologist Arthur Holmes championed the theory of continental drift at a time when it was deeply unfashionable. He proposed in 1931 that

7161-500: The shapes of continents on opposite sides of the Atlantic Ocean (most notably, Africa and South America) seem to fit together. W. J. Kious described Ortelius's thoughts in this way: Abraham Ortelius in his work Thesaurus Geographicus ... suggested that the Americas were "torn away from Europe and Africa ... by earthquakes and floods" and went on to say: "The vestiges of the rupture reveal themselves if someone brings forward

7254-400: The skeletal remains of Miocene fauna, but none provide the diversity of organisms, their interactions, or exquisite detail found at this site. The finely layered fossiliferous strata is associated with permanent water, perhaps an oxbow lake, in a mesic rainforest, habitat that once dominated the continent. At the time of deposition of the fossil strata, from 16 to 11 million years ago, the site

7347-714: The southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan . As the southern part of Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced to the north over time. The asthenospheric window associated to the triple junction disturbed previous patterns of mantle convection beneath Patagonia inducing an uplift of ca. 1 km that reversed

7440-516: The theory became known as the Permanence theory . This appeared to be confirmed by the exploration of the deep sea beds conducted by the Challenger expedition , 1872–1876, which showed that contrary to expectation, land debris brought down by rivers to the ocean is deposited comparatively close to the shore on what is now known as the continental shelf . This suggested that the oceans were

7533-399: The theory still required work to avoid foundering on the orogeny and isostasy objections. Worse, the most viable forms of the theory predicted the existence of convection cell boundaries reaching deep into the Earth, that had yet to be observed. In 1947, a team of scientists led by Maurice Ewing confirmed the existence of a rise in the central Atlantic Ocean, and found that the floor of

7626-604: The west coast of South America are thought to be caused by a regional phenomenon while the steadily rising central segment of the Andes represents an exception. While there are numerous registers of Oligocene–Miocene transgressions around the world it is doubtful that these correlate. It is thought that the Oligocene–Miocene transgression in Patagonia could have temporarily linked the Pacific and Atlantic Oceans, as inferred from

7719-423: Was Allodesmus . A ferocious walrus , Pelagiarctos may have preyed upon other species of pinnipeds including Allodesmus . Furthermore, South American waters witnessed the arrival of Megapiranha paranensis , which were considerably larger than modern age piranhas . New Zealand 's Miocene fossil record is particularly rich. Marine deposits showcase a variety of cetaceans and penguins , illustrating

7812-624: Was a gradual and progressive trend of increasing aridification, though it was not unidirectional, and wet humid episodes continued to occur. Between 7 and 5.3 Ma, temperatures dropped sharply again in the Late Miocene Cooling (LMC), most likely as a result of a decline in atmospheric carbon dioxide and a drop in the amplitude of Earth's obliquity, and the Antarctic ice sheet was approaching its present-day size and thickness. Ocean temperatures plummeted to near-modern values during

7905-407: Was a slow moving or still water body, perhaps a billabong . Along with fish, the fossilised remains of insects include an abundance of pupae and adult stages of aquatic species. Evidence of an isolated ecosystem at a stable and permanently wet site is supported by preliminary examination of taxa that includes midges. Miocene As Earth went from the Oligocene through the Miocene and into

7998-464: Was arid, particularly so during the Middle Miocene. Climates remained moderately warm, although the slow global cooling that eventually led to the Pleistocene glaciations continued. Although a long-term cooling trend was well underway, there is evidence of a warm period during the Miocene when the global climate rivalled that of the Oligocene . The climate of the Miocene has been suggested as

8091-493: Was held in Frankfurt . This conference came to be dominated by the fixists, especially as those geologists specializing in tectonics were all fixists except Willem van der Gracht. Criticism of continental drift and mobilism was abundant at the conference not only from tectonicists but also from sedimentological (Nölke), paleontological (Nölke), mechanical (Lehmann) and oceanographic ( Troll , Wüst ) perspectives. Hans Cloos ,

8184-403: Was initially sceptical of Tharp's observations that her maps confirmed continental drift theory, provided essential corroboration, using her skills in cartography and seismographic data, to confirm the theory. Geophysicist Jack Oliver is credited with providing seismologic evidence supporting plate tectonics which encompassed and superseded continental drift with the article "Seismology and

8277-688: Was inversely correlated with carbon dioxide levels and global temperatures during the Miocene. Most modern lineages of diatoms appeared by the Late Miocene. There is evidence from oxygen isotopes at Deep Sea Drilling Program sites that ice began to build up in Antarctica about 36 Ma during the Eocene . Further marked decreases in temperature during the Middle Miocene at 15 Ma probably reflect increased ice growth in Antarctica. It can therefore be assumed that East Antarctica had some glaciers during

8370-646: Was most intense there. Around this time the Mi3b glacial event (a massive expansion of Antarctic glaciers) occurred. The East Antarctic Ice Sheet (EAIS) markedly stabilised following the MMCT. The intensification of glaciation caused a decoherence of sediment deposition from the 405 kyr eccentricity cycle. The MMWI ended about 11 Ma, when the Late Miocene Cool Interval (LMCI) started. A major but transient warming occurred around 10.8-10.7 Ma. During

8463-414: Was not talking to us about continental drift and I was told, sneeringly, that if I could prove there was a force that could move continents, then he might think about it. The idea was moonshine, I was informed." As late as 1953—just five years before Carey introduced the theory of plate tectonics —the theory of continental drift was rejected by the physicist Scheidegger on the following grounds. From

8556-458: Was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites , suggested the existence of the supercontinent of Gondwana , which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, based on continents' current positions and orientations, and supported

8649-502: Was unable to provide a convincing explanation for the physical processes which might have caused this drift. He suggested that the continents had been pulled apart by the centrifugal pseudoforce ( Polflucht ) of the Earth's rotation or by a small component of astronomical precession , but calculations showed that the force was not sufficient. The Polflucht hypothesis was also studied by Paul Sophus Epstein in 1920 and found to be implausible. Although now accepted, and even with

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