Supercontinent

Supercontinent

Overview


In geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

, a supercontinent is a landmass
Landmass
A landmass is a contiguous area of land surrounded by ocean. Although it may be most often written as one word to distinguish it from the usage "land mass"—the measure of land area—it is also used as two words.Landmasses include:*supercontinents...

 comprising more than one continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

al core, or craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

. The assembly of cratons and accreted terranes
Terrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...

 that form Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

 qualifies as a supercontinent today.

Most commonly, paleogeographers employ the term supercontinent to refer to a single landmass consisting of all the modern continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

s. The earliest known supercontinent was Vaalbara
Vaalbara
Vaalbara is theorized to be Earth's first supercontinent, beginning its formation about , completing its formation by about and breaking up by . The name Vaalbara is derived from the South African Kaapvaal craton and the West Australian Pilbara craton...

. It formed from proto-continents and was a supercontinent by 3.1 billion years ago (3.1 Ga).
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In geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

, a supercontinent is a landmass
Landmass
A landmass is a contiguous area of land surrounded by ocean. Although it may be most often written as one word to distinguish it from the usage "land mass"—the measure of land area—it is also used as two words.Landmasses include:*supercontinents...

 comprising more than one continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

al core, or craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

. The assembly of cratons and accreted terranes
Terrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...

 that form Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

 qualifies as a supercontinent today.

History


Most commonly, paleogeographers employ the term supercontinent to refer to a single landmass consisting of all the modern continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

s. The earliest known supercontinent was Vaalbara
Vaalbara
Vaalbara is theorized to be Earth's first supercontinent, beginning its formation about , completing its formation by about and breaking up by . The name Vaalbara is derived from the South African Kaapvaal craton and the West Australian Pilbara craton...

. It formed from proto-continents and was a supercontinent by 3.1 billion years ago (3.1 Ga). Vaalbara
Vaalbara
Vaalbara is theorized to be Earth's first supercontinent, beginning its formation about , completing its formation by about and breaking up by . The name Vaalbara is derived from the South African Kaapvaal craton and the West Australian Pilbara craton...

 broke up ~2.8 Ga ago. The supercontinent Kenorland
Kenorland
Kenorland was one of the earliest supercontinents on Earth. It is believed to have formed during the Neoarchaean Era ~2.7 billion years ago by the accretion of Neoarchaean cratons and the formation of new continental crust...

 was formed ~2.7 Ga ago and then broke sometime after 2.5 Ga into the proto-continent Craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

s called Laurentia
Laurentia
Laurentia is a large area of continental craton, which forms the ancient geological core of the North American continent...

, Baltica
Baltica
Baltica is a name applied by geologists to a late-Proterozoic, early-Palaeozoic continent that now includes the East European craton of northwestern Eurasia. Baltica was created as an entity not earlier than 1.8 billion years ago. Before this time, the three segments/continents that now comprise...

, Australia
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...

, and Kalahari
Kalahari craton
The Kalahari craton is a craton, an old and stable part of the continental lithosphere with thick crust and deep lithospheric roots extending up to a few hundred kilometers into the Earth's mantle, that occupies a large portion of South Africa and consists of the Kaapvaal, the Zimbabwe craton, the...

. The supercontinent Columbia
Columbia (supercontinent)
Columbia, also known as Nuna and Hudsonland, was one of Earth's oldest supercontinents. It was first proposed by J.J.W. Rogers and M. Santosh and is thought to have existed approximately 1.8 to 1.5 billion years ago in the Paleoproterozoic Era. Zhao et al...

 or Nuna formed during a period of 2.0–1.8 billion years and broke up about 1.5–1.3 billion years ago.

The supercontinent Rodinia
Rodinia
In geology, Rodinia is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era...

 formed about 1.1 billion years ago and broke up roughly 750 million years ago. One of the fragments included large parts of the continents now located in the southern hemisphere. Plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

 brought the fragments of Rodinia back together in a different configuration during the late Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

 era about 300 million years ago, forming the best-known supercontinent, Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....

. Pangaea subsequently broke up into the northern and southern supercontinents, Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...

 and Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...

, about 200 million years ago.

Mechanism of generation and dispersal


The continental lithosphere is 80 – thick. When continents rift into separate plates, the thicker lithosphere gives way to thinner lithosphere of the oceans. Also, the transition from a continental rift to an oceanic rift is accompanied by block faulting, where blocks of continental crust drop down along extensional faults where the crust is being pulled apart. This results in a deep rift valley and a thinning of the crust. The African rift valley
East African Rift
The East African Rift is an active continental rift zone in eastern Africa that appears to be a developing divergent tectonic plate boundary. It is part of the larger Great Rift Valley. The rift is a narrow zone in which the African Plate is in the process of splitting into two new tectonic plates...

 is an active rifting event. Rifting of a continent begins with hot-spot volcanism at rift valleys. Hot spots burn holes through the crust and cause it to weaken. The crust under a rift is only 30 – thick.

Because the continental crust is so much thicker than the oceanic crust, it conducts heat less efficiently, making it function like an insulating blanket. If a supercontinent covers a portion of the earth’s surface where heat from the mantle accumulates under the crust, it causes the land mass to dome upward. This creates a superswell. The continued bulging causes supercontinents to rift apart with individual, broken-off continents sliding off the superswell. The continents then move toward colder sinking regions in the mantle and become stranded over cool downflows of mantle rock. After the continents are separated, heat from the mantle is more easily conducted through the newly formed ocean basin. After so much heat has escaped, the continents halt their outward progress and begin to return to their places of origin.

The landmasses surrounding the Pacific Basin apparently have not undergone continental collision. The Pacific Basin has narrowed and widened in response to the continental breakup dispersal and reconvergence in the area of the Atlantic Ocean. When today’s continents have reached their maximum dispersal (millions of years from now), the crust of the Atlantic Ocean bordering the continents will grow dense enough to sink into the mantle; creating subduction zones around the Atlantic Basin. This subduction into the mantle will begin the process of closing the Atlantic Basin. Eventually all continents will rejoin into another supercontinent over a large mantle downflow and the cycle of dispersal and rejoining will begin again.

The cycle of rifting and patching repeats itself roughly every 450 million years.

See also


  • Superocean
    Superocean
    A superocean is an ocean which surrounds a supercontinent. It is less commonly defined as any ocean larger than the current Pacific Ocean. Named global superoceans include Mirovia, which surrounded the supercontinent Rodinia, and Panthalassa, which surrounded the supercontinent Pangaea...

    s
  • Plate tectonics
    Plate tectonics
    Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

  • List of supercontinents
  • Supercontinent cycle
    Supercontinent cycle
    The supercontinent cycle describes the quasi-periodic aggregation and dispersal of Earth's continental crust. There are varying opinions as to whether the amount of continental crust is increasing, decreasing, or staying about the same, but it is agreed that the Earth's crust is constantly being...



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