Supercontinent

A supercontinent is a cohesive, all or at least almost all continental cratons or cores of the earth uniting within itself land mass that occurs over geological time by the movement of lithospheric plates, and then decays again ( Wilson cycle). The most famous and at the same time is the most recent supercontinent Pangaea, the ( 275-200 mya ) was in the Permian and the Triassic.

The boundary of the super continent to continent United is fluid. It is sometimes also largely contiguous land mass, which currently consists of the continents of Europe, Asia and Africa, classified as large or super continent of Africa - Eurasia.

The large and extra continents of the earth's

Including all the major continents of Eurasia and Africa - Eurasia and possible future supercontinent ( Pangaea Ultima or Amasien in about 250 to 400 million years ago ) there were on earth several - more or less scientifically controversial - Wholesale and supercontinents:

• Laurasia in the younger Mesozoic and early Paleogene - about 200-55 mya. The northern super continent existed after the breakup of Pangaea to the opening of the North Atlantic and included the present-day continental blocks North America and Eurasia.
• Pangaea in the late Paleozoic and early Mesozoic - about 275-200 mya - the youngest of the "real" super continents of the earth's history and the only one whose configuration is largely uncontroversial. It was created by the closure of Rheischen Ocean and the Ural Ocean and the subsequent collision with Gondwana Laurussias or Sibiria - Kasachstania (present-day West Asia ). The collision had, inter alia, the Variscan orogeny resulted. The huge bay in the west of this C -shaped supercontinent called Tethys Sea. The southern part of the young Pangaea - the old Gondwana - was affected by the so-called Permokarbonen ice age.
• Laurussia in the Paleozoic - about 400 mya to 300. Was primarily attributable to the closure of the Iapetus Ocean, followed by collision of the continents Laurentia ( " Ur - North America " ) and Baltica ( " Ur - Europe "). This collision and the collision of smaller island arcs and small continents ( Avalonia ) with Laurentia and / or Baltica led to the Caledonian orogeny. The Devonian Molassesedimenten of the Caledonian Mountains in what is now Western Europe, the so-called Old Red Sandstone, Laurussia owes the name Old- Red- continent.
• Gondwana from the latest Neoproterozoic to the Mesozoic - mya about 550-150. The durable great southern continent was formed by the detachment of the Phanerozoic northern continents Baltica, and Laurentia Sibiria of Pannotia and included the present continents South America, Africa (including the Arab Peninsula), Antarctica and Australia (including New Guinea ) and the Indian subcontinent. Whether Antarctica and Australia ( Australasian Antarctic ) were already at the time of separation of the northern continents components Pannotias (and thus Gondwana ) is controversial. In the following year, millions broke away again and again smaller continental sliver from the northern edge of Gondwana ( the so-called perigondwanischen Terrane, including Avalonia ), drifted northward and collided with the northern continents.
• Pannotia in younger Neoproterozoic - about 600-550 mya. Originated by collision of the fragments Rodinias. Northern Rodinia, South Rodinia and Congo - continent The mountain building associated with the formation Pannotias are summarized under the term Pan-African orogeny ( Brasiliano Orogeny, Cadomian orogeny ). Whether North Rodinia was involved as a closed, formed into large continent in the formation Pannotias is controversial. Maybe Australasian Antarctic is "docked" until later in the north-west edge of the northern part Pannotias. Maybe this happened even after drift of Phanerozoic northern continents, so Pannotia never existed as a "real" super-continent.
• Rodinia in the younger Proterozoic - about 1100-750 mya - is considered the first "real" super-continent of Earth's history. His constellation and the timing of its formation, however, are controversial. At the end of its existence it came to the first secured, possibly even global glaciation of the Earth, the so-called Snowball Earth with highlight in Cryogenium. The mountain building associated with the formation Rodinias are summarized under the term Grenville orogeny ( Svekonorwegische orogeny, Sunsás orogeny ).
• Columbia in the Paleoproterozoic - 1800-1500 mya - is regarded as hypothetical as well as its constituent parts Nena and Atlantica.
• Kenorland in the Paleoproterozoic - 2450-2110 mya - is considered paläomagnetisch likely. Traces indicate a glaciation, called the Huron ice age.
• Ur in the early Archean - 3000-1000 mya - is regarded as hypothetical - as well as his possible brother continent Arktica - 2,500 mya.

The last listed wholesale and Super Continents of the older Precambrian ( Ur, Kenorland, Columbia) were back in their size significantly behind later structures of this type, since the earth's crust at this time only a few small areas with differentiated continental crust had that could collide with each other. The oldest rocks of the earth at all - the Nuvvuagittuq greenstone belt of the Superior craton and the Acasta - Gneiss from the Slave craton of the Canadian Shield - is more than 4 billion years old and show that even in the Hadean existed mainland islands.

Influence of supercontinents on climate and biota

When all the continents are united into a landmass, this has an impact on the climate: There are few irrigated coastlines and more arid areas in the interior of the continent. An example of such a development in the interior of a large continent today are the drylands in Central Asia ( Gobi, Taklamakan ).

The biodiversity is affected by the transition of a large into smaller multiple continents: The propagation of terrestrial organisms on a single continent is simple and therefore the biodiversity there is rather low. Only the splitting into several continents leads to complete isolation of individual populations of the species, from which will always be new species.

Evidence for the existence of supercontinents

The review of the supercontinent or Wilson - cycle hypothesis can be done for example by examining the isotope geochemistry of sedimentary rocks. For this purpose, were in the following two examples will be given:

• Sulfur: Heavy isotopes of an element fall into a supersaturated solution from earlier than light. Therefore it is expected that form in geological epochs in which there are many Evaporitbecken in which sulfate- rich deposits (i.e. L. gypsum) and their water but is still to some extent in the exchange with the ocean, the proportion the lighter 32S isotope is increased in the ocean compared to the proportion of the heavier 34S isotope. If we assume also that the number of Evaporitbecken is particularly high when a supercontinent in the first phase of the Wilson cycle is ( advanced Continental Rifts or narrow ocean basin with connection to the sea ), should have a high 32S/34S-Verhältnis ( δ 34S ) in open - marine sediments show the existence of a nascent in disrepair supercontinent. Corresponding studies on open - marine sediments actually returned elevated δ 34S values ​​for the period about 200 million years ago and 600 million years ago, for the beginning of the disintegration of Pangaea or Pannotias is assumed.

• Strontium and osmium is the case of chemical weathering of calcium and magnesium silicates, the greenhouse gas carbon dioxide ( CO2) from the atmosphere in the form of bicarbonate (HCO3-) and transported via rivers into the sea, where it is mainly in the form of calcium carbonate ( calcite ) again fails and is thus removed for geological periods from the atmosphere. This in turn affects the global climate. In the said case is a weakening of the greenhouse effect, that is, a cooling of the global climate (English: icehouse ), instead, as less CO2 can retain less heat radiated from the earth's surface into the atmosphere. An important causative factor for the stubbornness tables glaciation is therefore in the beginning of the breakup Rodinias and the emergence of the so-called Laurentian Igneous Province in low latitudes suspected ( " Fire and Ice " hypothesis ): The grave fracture tectonics during the opening of the proto - Pacific basin was associated with a volcanism, were encouraged by the large volumes of basic magma to the surface. The weathering of the corresponding geologically young, strong Ca - and Mg - containing silicate rocks (basalt, etc.) in this regard aggressive equatorial climate eluded the atmosphere much CO2. This assumption is supported by low 187Os/188Os- and 87Sr/86Sr-Verhältnisse in carbonate rocks below and above the stubbornness of Glazialablagerungen tables icing. 187Os and 87Sr are stable decay products of 187Re or 87Rb. The latter have an extremely long half-life (about 41 or 48 billion years). In addition, in the formation of magma deep within the earth, the parent isotopes 187Re and 87Rb go in preference to their decay products into the melt. Therefore, primary 187Os and 87Sr can accumulate only by the weathering of very old continental crust in sediments, which in turn means that low 187Os/188Os- and 87Sr/86Sr-Verhältnisse may indicate increased continental weathering relatively young igneous rocks in the period of deposition of the studied sedimentary rocks.