thumb|upright=1.35|The supercontinent of [[Pangaea with the positions of the continents at the Permian-Triassic boundary, about 250 Ma. AR=Amuria; NC=North China; SC=South China; PA=Panthalassic Ocean; PT=Paleotethys Ocean; NT=Neotethys Ocean. Orogens shown in red. Subduction zones shown in black. Spreading centers shown in green.]]

thumb|Although not a supercontinent, the current [[Afro-Eurasian landmass contains about 57% of Earth's land area.]]

In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leaves room for interpretation and is easier to apply to Precambrian times. To separate supercontinents from other groupings, a limit has been proposed in which a continent must include at least about 75% of the continental crust then in existence in order to qualify as a supercontinent.

Moving under the forces of plate tectonics, supercontinents have assembled and dispersed multiple times in the geologic past. According to modern definitions, a supercontinent does not exist today; Pangaea's predecessor Gondwana is not considered a supercontinent under the first definition since the landmasses of Baltica, Laurentia and Siberia were separate at the time.

A future supercontinent, termed Pangaea Proxima, is hypothesized to form within the next 250 million years.

Theories

The Phanerozoic supercontinent Pangaea began to break up and this distancing continues today. Because Pangaea is the most recent of Earth's supercontinents, it is the best known and understood. Contributing to Pangaea's popularity in the classroom, its reconstruction is almost as simple as fitting together the present continents bordering the Atlantic ocean like puzzle pieces. However, before completely breaking up, some fragments of Rodinia had already come together to form Gondwana by . Pangaea formed through the collision of Gondwana, Laurasia (Laurentia and Baltica), and Siberia.

Protopangea–Paleopangea

The second model (Kenorland-Arctica) is based on both palaeomagnetic and geological evidence and proposes that the continental crust comprised a single supercontinent from until break-up during the Ediacaran period after . The reconstruction is derived from the observation that palaeomagnetic poles converge to quasi-static positions for long intervals between ~2.72–2.115 Ga; 1.35–1.13 Ga; and with only small peripheral modifications to the reconstruction. During the intervening periods, the poles conform to a unified apparent polar wander path.

Although it contrasts the first model, the first phase (Protopangea) essentially incorporates Vaalbara and Kenorland of the first model. The explanation for the prolonged duration of the Protopangea–Paleopangea supercontinent appears to be that lid tectonics (comparable to the tectonics operating on Mars and Venus) prevailed during Precambrian times. According to this theory, plate tectonics as seen on the contemporary Earth became dominant only during the latter part of geological times.

Cycles

A supercontinent cycle is the break-up of one supercontinent and the development of another, which takes place on a global scale.

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| Ur || 2,803–2,408 || Mesoarchean-Siderian ||Described as both a continent

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| Kenorland || 2,720–2,114 || Neoarchean-Rhyacian ||Alternatively the continents may have formed into two groupings Superia and Sclavia

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| Pangaea || 336–175 || Carboniferous-Jurassic ||

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Volcanism

<!-- Deleted image removed: [[File:FigureSlabAvalanche.jpg|thumb|As the slab is subducted into the mantle, the more dense material will break off and sink to the lower mantle creating a discontinuity elsewhere known as a slab avalanche

Dispersal of supercontinents is caused by the accumulation of heat underneath the crust due to the rising of very large convection cells or plumes, and a massive heat release resulted in the final break-up of Paleopangea. Accretion occurs over geoidal lows that can be caused by avalanche slabs or the downgoing limbs of convection cells. Evidence of the accretion and dispersion of supercontinents is seen in the geological rock record.

The influence of known volcanic eruptions does not compare to that of flood basalts. The timing of flood basalts has corresponded with a large-scale continental break-up. However, due to a lack of data on the time required to produce flood basalts, the climatic impact is difficult to quantify. The timing of a single lava flow is also undetermined. These are important factors on how flood basalts influenced paleoclimate. Glaciers have major implications on the climate, particularly through sea level change. Changes in the position and elevation of the continents, the paleolatitude and ocean circulation affect the glacial epochs. There is an association between the rifting and breakup of continents and supercontinents and glacial epochs. However, some geologists disagree and think that there was a temperature increase at this time. This increase may have been strongly influenced by the movement of Gondwana across the South Pole, which may have prevented lengthy snow accumulation. Although late Ordovician temperatures at the South Pole may have reached freezing, there were no ice sheets during the early Silurian through the late Mississippian When any supercontinent breaks up, there will be an increase in precipitation runoff over the surface of the continental landmasses, increasing silicate weathering and the consumption of CO<sub>2</sub>.

Cold winters in continental interiors are due to rate ratios of radiative cooling (greater) and heat transport from continental rims. To raise winter temperatures within continental interiors, the rate of heat transport must increase to become greater than the rate of radiative cooling. Through climate models, alterations in atmospheric CO<sub>2</sub> content and ocean heat transport are not comparatively effective.

  1. Continents collide
  2. Super-mountains form
  3. Erosion of super-mountains
  4. Large quantities of minerals and nutrients wash out to open ocean
  5. Explosion of marine algae life (partly sourced from noted nutrients)
  6. Mass amounts of oxygen produced during photosynthesis

The process of Earth's increase in atmospheric oxygen content is theorized to have started with the continent-continent collision of huge landmasses forming supercontinents, and therefore possibly supercontinent mountain ranges (super-mountains). These super-mountains would have eroded, and the mass amounts of nutrients, including iron and phosphorus, would have washed into oceans, just as is seen happening today. The oceans would then be rich in nutrients essential to photosynthetic organisms, which would then be able to respire mass amounts of oxygen. There is an apparent direct relationship between orogeny and the atmospheric oxygen content. There is also evidence for increased sedimentation concurrent with the timing of these mass oxygenation events, meaning that the organic carbon and pyrite at these times were more likely to be buried beneath sediment and therefore unable to react with the free oxygen. This sustained the atmospheric oxygen increases.

Proxies

<!-- Deleted image removed: thumb|U–Pb ages of 5,246 concordant detrital zircons from 40 of Earth's major rivers -->

Granites and detrital zircons have notably similar and episodic appearances in the rock record. Their fluctuations correlate with Precambrian supercontinent cycles. The U–Pb zircon dates from orogenic granites are among the most reliable aging determinants.

Some issues exist with relying on granite sourced zircons, such as a lack of evenly globally sourced data and the loss of granite zircons by sedimentary coverage or plutonic consumption. Where granite zircons are less adequate, detrital zircons from sandstones appear and make up for the gaps. These detrital zircons are taken from the sands of major modern rivers and their drainage basins.