Pangaea – Wikipedia

Supercontinent from the late Paleozoic to early Mesozoic earned run average
“ Pangaia ” redirects here. For for the Southeast Asian ( and late African ) native warships, see Penjajap
The supercontinent Pangaea in the early Mesozoic ( at 200 Ma

Pangaea or Pangea ( ) [ 1 ] was a supercontinent that existed during the late Paleozoic and early Mesozoic era. [ 2 ] It assembled from earlier continental units during the Carboniferous approximately 335 million years ago, and began to break apart about 200 million years ago, at the conclusion of the Triassic and begin of the Jurassic. [ 3 ] In contrast to the present Earth and its distribution of continental mass, Pangaea was centred on the Equator and surrounded by the superocean Panthalassa and the Paleo-Tethys and subsequent Tethys Oceans. Pangaea is the most recent supercontinent to have existed and the first to be reconstructed by geologists .

origin of the concept

Alfred Wegener c. 1924–1930 World map of Pangaea created by Alfred Wegener to illustrate his concept The name “ Pangaea ” is derived from Ancient Greek pan ( πᾶν, “ all, entire, whole ” ) and Gaia or Gaea ( Γαῖα, “ Mother Earth, land ” ). [ 4 ] [ 9 ] The concept that the continents once formed a adjacent domain mass was hypothesised, with corroborating evidence, by Alfred Wegener, the originator of the scientific theory of continental drift, in his 1912 issue The Origin of Continents ( Die Entstehung der Kontinente ). [ 10 ] He expanded upon his hypothesis in his 1915 record The Origin of Continents and Oceans ( Die Entstehung der Kontinente und Ozeane ), in which he postulated that, before breaking up and drifting to their present locations, all the continents had formed a unmarried supercontinent that he called the “ Urkontinent “. The name “ Pangaea ” occurs in the 1920 edition of Die Entstehung der Kontinente und Ozeane, but only once, when Wegener refers to the ancient supercontinent as “ the Pangaea of the Carboniferous ”. [ 11 ] Wegener used the Germanized form “ Pangäa, ” but the diagnose enter German and English scientific literature ( in 1922 [ 12 ] and 1926, respectively ) in the Latinized form “ Pangaea ” ( of the greek “ Pangaia ” ), particularly due to a symposium of the American Association of Petroleum Geologists in November 1926. [ 13 ] Wegener originally proposed that the separation of Pangaea was due to centripetal forces from the Earth ‘s rotation acting on the high continents. however, this mechanism was easily shown to be physically implausible, which delayed credence of the Pangaea hypothesis. [ 14 ] Arthur Holmes proposed the more plausible mechanism of mantle convection, [ 15 ] which, together with testify provided by the map of the ocean floor following the second World War, led to the development and acceptance of the theory of plate tectonics. This theory provides the now widely-accepted explanation for the universe and separation of Pangaea .

testify of universe

The distribution of fossils across the continents is one line of evidence pointing to the being of Pangaea. The geography of the continents bordering the Atlantic Ocean was the first tell suggesting the universe of Pangaea. The apparently close fit of the coastlines of North and South America with Europe and Africa was remarked on about arsenic soon as these coasts were charted. The first gear to suggest that these continents were once joined and late separated may have been Abraham Ortelius in 1596. careful reconstructions showed that the mismatch at the 500 fathoms ( 3,000 feet ; 910 meters ) contour was less than 130 kilometer ( 81 secret intelligence service ), and it was argued that this was much excessively good to be attributed to prospect. [ 18 ] extra testify for Pangaea is found in the geology of adjacent continents, including matching geological trends between the eastern coast of South America and the western coast of Africa. The polar frost crown of the Carboniferous Period covered the southern end of Pangaea. Glacial deposits, specifically till, of the same age and structure are found on many discriminate continents that would have been together in the celibate of Pangaea. [ 19 ] Fossil evidence for Pangaea includes the bearing of similar and identical species on continents that are now bang-up distances apart. For case, fossils of the therapsid Lystrosaurus have been found in South Africa, India and Antarctica, aboard members of the Glossopteris vegetation, whose distribution would have ranged from the polar circle to the equator if the continents had been in their present position ; similarly, the fresh water reptile Mesosaurus has been found in lone localize regions of the coasts of Brazil and West Africa. [ 20 ] Paleomagnetic study of apparent polar wandering paths besides support the theory of a supercontinent. Geologists can determine the movement of continental plates by examining the orientation of magnetic minerals in rocks ; when rocks are formed, they take on the magnetic properties of the Earth and indicate in which commission the poles lie relative to the rock. Since the charismatic poles drift about the rotational punt with a period of only a few thousand years, measurements from numerous lavas spanning several thousand years are averaged to give an apparent mean pivotal stead. Samples of sedimentary rock and intrusive igneous rock ‘n’ roll have magnetic orientations that are typically an average of the “ worldly variation ” in the orientation of magnetic north because their remanent magnetizations are not acquired instantaneously. magnetic differences between sample distribution groups whose age varies by millions of years is ascribable to a combination of genuine polar weave and the aimless of continents. The on-key pivotal wander component is identical for all samples, and can be removed, leaving geologists with the assign of this motion that shows continental drift and can be used to help reconstruct earlier continental positions. The continuity of batch chains provides far tell for Pangaea. One exemplar of this is the appalachian Mountains chain, which extends from the southeast United States to the Caledonides of Ireland, Britain, Greenland, and Scandinavia. [ 22 ]

constitution

appalachian orogeny Pangaea is entirely the most holocene supercontinent identified in the geological record. The imprint of supercontinents and their break up appears to have been cyclic through earth ‘s history. There may have been several others before Pangaea. Paleomagnetic measurements help geologists determine the latitude and predilection of ancient continental blocks, and newer techniques may help determine longitudes. [ 23 ] Paleontology helps determine ancient climates, confirming latitude estimates from paleomagnetic measurements, and the distribution of ancient forms of life provides clues on which continental blocks were close to each early at particular geological moments. [ 24 ] however, reconstructions of continents prior to the separation of Pangaea, including the ones in this section, remain partially inquisitive, and different reconstructions will differ in some details. [ 25 ]

previous supercontinents

The fourth-last supercontinent, called Columbia or Nuna, appears to have assembled in the period 2.0–1.8 billion years ago ( Ga ). [ 26 ] [ 27 ] Columbia/Nuna broke up and the next supercontinent, Rodinia, formed from the accretion and assembly of its fragments. Rodinia lasted from about 1.3 billion years ago until about 750 million years ago, but its claim shape and geodynamic history are not about angstrom well understand as those of the late supercontinents, Pannotia and Pangaea. [ 28 ] According to one reconstruction, [ 29 ] when Rodinia broke up, it split into three pieces : the supercontinent of Proto-Laurasia, the supercontinent of Proto-Gondwana, and the smaller Congo craton. Proto-Laurasia and Proto-Gondwana were separated by the Proto-Tethys Ocean. next Proto-Laurasia itself rip apart to form the continents of Laurentia, Siberia, and Baltica. Baltica moved to the east of Laurentia, and Siberia moved northeast of Laurentia. The burst besides created two newfangled oceans, the Iapetus Ocean and Paleoasian Ocean. Most of the above masses coalesced again to form the relatively ephemeral supercontinent of Pannotia. This supercontinent included boastfully amounts of land near the poles and, near the equator, only a relatively little comic strip connecting the polar masses. Pannotia lasted until 540 Ma, near the begin of the cambrian menstruation and then broke up, giving emanation to the continents of Laurentia, Baltica, and the southerly supercontinent of Gondwana. [ 31 ]

formation of Euramerica ( Laurussia )

In the welshman period, the continent of Laurentia, which would late become North America, sat on the equator, with three bordering oceans : the Panthalassic Ocean to the north and west, the Iapetus Ocean to the south, and the Khanty Ocean to the east. In the Earliest ordovician, around 480 Ma, the microcontinent of Avalonia – a landmass incorporating fragments of what would become eastern Newfoundland, the southerly british Isles, and parts of Belgium, northern France, Nova Scotia, New England, South Iberia, and northwest Africa – broke barren from Gondwana and began its journey to Laurentia. [ 32 ] Baltica, Laurentia, and Avalonia all came together by the end of the ordovician to form a landmass called Euramerica or Laurussia, closing the Iapetus Ocean. The collision besides resulted in the formation of the northern Appalachians. Siberia sat near Euramerica, with the Khanty Ocean between the two continents. While all this was happening, Gondwana drifted lento towards the South Pole. This was the first step of the formation of Pangaea .

collision of Gondwana with Euramerica

The second step in the geological formation of Pangaea was the collision of Gondwana with Euramerica. By the center of the Silurian, 430 Ma, Baltica had already collided with Laurentia, forming Euramerica, an event called the Caledonian orogeny. Avalonia had not so far collided with Laurentia, but as Avalonia inched towards Laurentia, the seaway between them, a end of the Iapetus Ocean, was slowly shrinking. meanwhile, southern Europe broke off from Gondwana and began to move towards Euramerica across the Rheic Ocean. It collided with southern Baltica in the Devonian. By the late silurian, Annamia and South China schism from Gondwana and started to head north, shrinking the Proto-Tethys Ocean in their way and opening the new Paleo-Tethys Ocean to their south. In the devonian Period, Gondwana itself headed towards Euramerica, causing the Rheic Ocean to shrink. In the Early Carboniferous, northwest Africa had touched the southeast coast of Euramerica, creating the southern part of the appalachian Mountains, the Meseta Mountains, and the Mauritanide Mountains, an event called the Variscan orogeny. South America moved north to southern Euramerica, while the eastern share of Gondwana ( India, Antarctica, and Australia ) headed toward the South Pole from the equator. North and South China were on freelancer continents. The Kazakhstania microcontinent had collided with Siberia. ( Siberia had been a divide continent for millions of years since the contortion of the supercontinent Pannotia in the Middle Carboniferous. ) The Variscan orogeny raised the Central Pangaean Mountains, which were comparable to the modern Himalayas in scale. With Pangaea nowadays stretching from the South Pole across the equator and well into the Northern Hemisphere, an intense megamonsoon climate was established, except for a constantly wet zone immediately around the central mountains. [ 36 ]

formation of Laurasia

western Kazakhstania collided with Baltica in the Late Carboniferous, closing the Ural Ocean between them and the western Proto-Tethys in them ( Uralian orogeny ), causing the formation of not only the Ural Mountains but besides the supercontinent of Laurasia. This was the end dance step of the geological formation of Pangaea. interim, South America had collided with southerly Laurentia, closing the Rheic Ocean and completing the Variscian orogeny with the formation the southernmost share of the Appalachians and Ouachita Mountains. By this time, Gondwana was positioned near the South Pole, and glaciers were forming in Antarctica, India, Australia, southern Africa, and South America. The North China obstruct collided with Siberia by Jurassic, wholly closing the Proto-Tethys Ocean. By the early on permian, the cimmerian plate split from Gondwana and headed towards Laurasia, thus closing the Paleo-Tethys Ocean, but forming a newfangled ocean, the Tethys Ocean, in its southern end. Most of the landmasses were all in one. By the Triassic Period, Pangaea rotated a little, and the cimmerian plate was still travelling across the shrinking Paleo-Tethys until the Middle Jurassic. By the late Triassic, the Paleo-Tethys had closed from west to east, creating the cimmerian Orogeny. Pangaea, which looked like a C, with the newfangled Tethys Ocean inside the C, had rifted by the Middle Jurassic, and its contortion is explained below .

paleogeography of Earth in the late welshman, around 490 Ma

paleogeography of Earth in the middle silurian, around 430 Ma. Avalonia and Baltica have fused with Laurentia to form Laurussia . paleogeography of Earth in the late Carboniferous, around 310 Ma. Laurussia has fused with Gondwana to form Pangea . paleogeography of the worldly concern at the Permian–Triassic limit, around 250 Ma. Siberia has fused with Pangaea to complete the forum of the supercontinent .

life

Dicroidium zuberi, an Early Triassic plant from Pangaea (present-day Argentina), an early triassic plant from Pangaea ( contemporary Argentina ) The four floristic provinces of the world at the Permian-Carboniferous limit, 300 million years ago Pangaea existed as a supercontinent for 160 million years, from its assembly around 335 million years ago ( Early Carboniferous ) to its dissolution 175 million years ago ( Middle Jurassic ). [ 3 ] During this interval, important developments in the evolution of life took station. The seas of the early Carboniferous were dominated by rugose corals, brachiopods, bryozoans, sharks, and the first gear bony pisces. Life on kingdom was dominated by lycopsid forests inhabited by insects and other arthropods and the first tetrapods. [ 39 ] By the time Pangaea broke up, in the Middle Jurassic, the seas swarmed with mollusk ( peculiarly ammonites ), [ 40 ] ichthyosaur, sharks and rays, and the first ray-finned bony fishes, while life on land was dominated by forests of cycads and conifers in which dinosaur flourished and in which the first on-key mammals had appeared. [ 41 ] [ 42 ] The evolution of life in this time interval of time reflected conditions created by the assembly of Pangaea. The forum of most of the continental crust into one landmass reduced the extent of ocean coasts. Increased erosion from uplifted continental crust increased the importance of floodplain and delta environments relative to shallow marine environments. Continental assembly and uplift besides meant an increasingly arid climate over a lot of the come on of the Earth. This favored the development of amniotes and seed plants, whose eggs and seeds were good adapted to dry climates. [ 39 ] The early dry course was most pronounce in western Pangaea, which became an epicenter for the development and geographic unfold of amniotes. [ 43 ] ember swamps are typically a sport of perpetually moisture regions close to the equator. The assembly of Pangaea disrupted the intertropical convergence zone and created an extreme monsoon climate that reduced the deposition of coal to its lowest level in the last 300 million years. During the Permian, coal deposition was largely restricted to the North and South China microcontinents, which were among the few areas of continental crust that had not joined with Pangaea. [ 44 ] The extremes of climate conditions in the interior of Pangaea are reflected in bone growth patterns of pareiasaurs and in the increase patterns in gymnosperm forests. [ 45 ]
Lystrosaurus fossil from South Africa early Triassicfossil from South Africa The lack of oceanic barriers is thought to have favored cosmopolitanism, in which species show a across-the-board geographic distribution. Cosmopolitanism was besides driven by mass extinctions, including the Permian–Triassic extinction event, the most severe in the dodo record, and besides the Triassic–Jurassic extinction event. These events resulted in disaster fauna showing little diverseness and high cosmopolitanism. These include Lystrosaurus, which opportunistically spread to every corner of Pangaea following the Permian–Triassic extinction event. [ 46 ] On the other hired hand, there is evidence that many Pangaean species were provincial, with a specify geographic range, in hurt of the lack of geographic barriers. This may be ascribable to the strong variations in climate by latitude and season produced by the extreme monsoon climate. [ 47 ] For exemplar, cold-adapted pteridosperms ( early seed plants ) of Gondwana were blocked from spreading throughout Pangaea by the warming climate, and northern pteridosperms ended up dominating Gondwana in the Triassic .

Mass extinctions

The tectonics and geography of Pangaea may have worsened the Permian–Triassic extinction event or early extinctions. For example, the deoxidize area of continental shelf environments may have left marine species vulnerable to extinction. [ 49 ] however, no evidence for a species-area impression has been found in more late and better characterized portions of the geological record. [ 50 ] Another possibility is that reduce sea-floor go around associated with the formation of Pangaea, and the resulting cool and cave in of oceanic crust, may have reduced the number of islands that could have served as refugia for marine species. Species diverseness may have already been reduced prior to mass extinction events due to mingling of species possible when once separate continents were merged. however, there is potent attest that climate barriers continued to separate ecological communities in different parts of Pangaea. The eruptions of the Emeishan Traps may have eliminated South China, one of the few continental areas not merged with Pangaea, as a refugium .

Rifting and break-up

The dissolution of Pangaea over time There were three major phases in the break-up of Pangaea .

opening of the Atlantic

The Atlantic Ocean did not open uniformly ; rifting began in the north-central Atlantic. The first separation of Pangaea is proposed for the late Ladinian ( 230 Ma ) with initial spreading in the open cardinal Atlantic. then the rifting proceeded along the eastern allowance of North America, the northwest african allowance and the High, Saharan and Tunisian Atlas. [ 53 ] Another phase began in the early on – middle Jurassic ( about 175 Ma ), when Pangaea began to rift from the Tethys Ocean in the east to the Pacific Ocean in the west. The rifting that took place between North America and Africa produced multiple fail rifts. One rift resulted in a new ocean, the North Atlantic Ocean. [ 22 ] The South Atlantic did not open until the Cretaceous when Laurasia started to rotate clockwise and moved northbound with North America to the north, and Eurasia to the south. The clockwise motion of Laurasia led much later to the conclude of the Tethys Ocean and the widening of the “ Sinus Borealis ”, which late became the Arctic Ocean. interim, on the early slope of Africa and along the adjacent margins of east Africa, Antarctica and Madagascar, new rifts were forming that would lead to the constitution of the southwest indian Ocean that would open up in the Cretaceous .

Break-up of Gondwana

The second base major phase in the break-up of Pangaea began in the early Cretaceous ( 150–140 Ma ), when the landmass of Gondwana separated into multiple continents ( Africa, South America, India, Antarctica, and Australia ). The subduction at Tethyan Trench credibly caused Africa, India and Australia to move north, causing the unfold of a “ South indian Ocean ”. In the Early Cretaceous, Atlantica, today ‘s South America and Africa, ultimately separated from easterly Gondwana ( Antarctica, India and Australia ). then in the Middle Cretaceous, Gondwana fragmented to open up the South Atlantic Ocean as South America started to move westbound off from Africa. The South Atlantic did not develop uniformly ; preferably, it rifted from south to north. besides, at the same time, Madagascar and India began to separate from Antarctica and moved northbound, opening up the indian Ocean. Madagascar and India separated from each other 100–90 Ma in the Late Cretaceous. India continued to move north toward Eurasia at 15 centimeters ( 6 in ) a year ( a plate tectonic read ), closing the easterly Tethys Ocean, while Madagascar stopped and became locked to the african Plate. New Zealand, New Caledonia and the pillow of Zealandia began to separate from Australia, moving eastbound toward the Pacific and opening the Coral Sea and Tasman Sea .

open of the norwegian Sea and break-up of Australia and Antarctica

The third gear major and concluding phase of the break-up of Pangaea occurred in the early Cenozoic ( Paleocene to Oligocene ). Laurasia split when North America/Greenland ( besides called Laurentia ) broke free from Eurasia, opening the norwegian Sea about 60–55 Ma. The Atlantic and indian Oceans continued to expand, closing the Tethys Ocean. meanwhile, Australia schism from Antarctica and moved promptly north, equitable as India had done more than 40 million years ahead. Australia is presently on a collision course with eastern Asia. Both Australia and India are presently moving northeast at 5–6 centimeters ( 2–3 in ) a class. Antarctica has been near or at the South Pole since the constitution of Pangaea about 280 Ma. India started to collide with Asia beginning about 35 Ma, forming the Himalayan orogeny, and besides ultimately closing the Tethys Seaway ; this collision continues today. The african Plate started to change directions, from west to northwest toward Europe, and South America began to move in a northbound direction, separating it from Antarctica and allowing complete oceanic circulation around Antarctica for the first time. This motion, together with decreasing atmospheric carbon dioxide concentrations, caused a rapid cooling system of Antarctica and allowed glaciers to form. This glaciation finally coalesced into the kilometers-thick ice rink sheets seen today. [ 54 ] early major events took identify during the Cenozoic, including the hatchway of the Gulf of California, the upheaval of the Alps, and the open of the Sea of Japan. The break-up of Pangaea continues nowadays in the Red Sea Rift and East African Rift .

Climate change after Pangaea

The dissolution of Pangaea was accompanied by outgassing of big quantities of carbon dioxide from continental rifts. This produced a Mesozoic CO2 High that contributed to the very warm climate of the early Cretaceous. [ 55 ] The open of the Tethys Ocean besides contributed to the calefacient of the climate. The very active mid-ocean ridges associated with the separation of Pangaea raised ocean levels to the highest in the geological record, flooding much of the continents. [ 57 ] The expansion of the temperate climate zones that accompanied the separation of Pangaea may have contributed to the diversification of the angiosperms. [ 58 ]

See besides

References

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