Supercontinent

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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. Pangea assembly 250.png
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.
Although not a supercontinent, the current Afro-Eurasian landmass contains about 57% of Earth's land area. Afro-Eurasia.png
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. [1] [2] [3] 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. [4] 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. [5]

Contents

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; [1] the closest is the current Afro-Eurasian landmass, which covers approximately 57% of Earth's total land area. The last period in which the continental landmasses were near to one another was 336 to 175 million years ago, forming the supercontinent Pangaea. The positions of continents have been accurately determined back to the early Jurassic, shortly before the breakup of Pangaea. [6] 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. [7]

A future supercontinent, termed Pangaea Proxima, is hypothesized to form within the next 250 million years. [8]

Theories

The Phanerozoic supercontinent Pangaea began to break up 215 Ma 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. [4]

For the period before Pangaea, there are two contrasting models for supercontinent evolution through geological time.

Series

The first model theorizes that at least two separate supercontinents existed comprising Vaalbara and Kenorland, with Kenorland comprising Superia and Sclavia. These parts of Neoarchean age broke off at ~2480 and 2312 Ma, and portions of them later collided to form Nuna (Northern Europe and North America). Nuna continued to develop during the Mesoproterozoic, primarily by lateral accretion of juvenile arcs, and in ~1000 Ma Nuna collided with other land masses, forming Rodinia. [4] Between ~825 and 750 Ma Rodinia broke apart. [9] However, before completely breaking up, some fragments of Rodinia had already come together to form Gondwana by ~608 Ma. 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 ~2.72 Ga until break-up during the Ediacaran period after ~0.573 Ga. The reconstruction [10] 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 0.75–0.573 Ga with only small peripheral modifications to the reconstruction. [11] 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. [11] This approach was widely criticized by many researchers as it uses incorrect application of paleomagnetic data. [12]

Cycles

A supercontinent cycle is the break-up of one supercontinent and the development of another, which takes place on a global scale. [4] Supercontinent cycles are not the same as the Wilson cycle, which is the opening and closing of an individual oceanic basin. The Wilson cycle rarely synchronizes with the timing of a supercontinent cycle. [1] However, supercontinent cycles and Wilson cycles were both involved in the creation of Pangaea and Rodinia. [6]

Secular trends such as carbonatites, granulites, eclogites, and greenstone belt deformation events are all possible indicators of Precambrian supercontinent cyclicity, although the Protopangea–Paleopangea solution implies that Phanerozoic style of supercontinent cycles did not operate during these times. Also, there are instances where these secular trends have a weak, uneven, or absent imprint on the supercontinent cycle; secular methods for supercontinent reconstruction will produce results that have only one explanation, and each explanation for a trend must fit in with the rest. [4]

The following table names reconstructed ancient supercontinents, using Bradley's 2011 looser definition, [7] with an approximate timescale of millions of years ago (Ma).

Supercontinent nameAge (Ma)Period/Era RangeComment
Vaalbara 3,636–2,803Eoarchean-MesoarcheanAlso described as a supercraton or just a continent [13]
Ur 2,803–2,408Mesoarchean-SiderianDescribed as both a continent [2] and a supercontinent [14]
Kenorland 2,720–2,114Neoarchean-RhyacianAlternatively the continents may have formed into two groupings Superia and Sclavia [15] [4]
Arctica 2,114–1,995Rhyacian-OrosirianNot generally regarded as a supercontinent, depending on definition [2]
Atlantica 1,991–1,124Orosirian-StenianNot generally regarded as a supercontinent, depending on definition [2]
Columbia (Nuna) 1,820–1,350Orosirian-Ectasian [15]
Rodinia 1,130–750Stenian-Tonian [15]
Pannotia 633–573Ediacaran [15]
Gondwana 550–175Ediacaran-JurassicFrom the Carboniferous, formed part of Pangaea, [4] not always regarded as a supercontinent [16]
Pangaea 336–175Carboniferous-Jurassic

Volcanism

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 FigureSlabAvalanche.jpg
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
The effects of mantle plumes possibly caused by slab avalanches elsewhere in the lower mantle on the breakup and assembly of supercontinents FigureSupercontinentBreakup.jpg
The effects of mantle plumes possibly caused by slab avalanches elsewhere in the lower mantle on the breakup and assembly of supercontinents

The causes of supercontinent assembly and dispersal are thought to be driven by convection processes in Earth's mantle. Approximately 660 km into the mantle, a discontinuity occurs, affecting the surface crust through processes involving plumes and superplumes (aka large low-shear-velocity provinces). When a slab of the subducted crust is denser than the surrounding mantle, it sinks to discontinuity. Once the slabs build up, they will sink through to the lower mantle in what is known as a "slab avalanche". This displacement at the discontinuity will cause the lower mantle to compensate and rise elsewhere. The rising mantle can form a plume or superplume. [1]

Besides having compositional effects on the upper mantle by replenishing the large-ion lithophile elements, volcanism affects plate movement. [1] The plates will be moved towards a geoidal low perhaps where the slab avalanche occurred and pushed away from the geoidal high that can be caused by the plumes or superplumes. This causes the continents to push together to form supercontinents and was evidently the process that operated to cause the early continental crust to aggregate into Protopangea. [17]

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. [18] 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. [6]

Plate tectonics

Global palaeogeography and plate interactions as far back as Pangaea are relatively well understood today. However, the evidence becomes more sparse further back in geologic history. Marine magnetic anomalies, passive margin match-ups, geologic interpretation of orogenic belts, paleomagnetism, paleobiogeography of fossils, and distribution of climatically sensitive strata are all methods to obtain evidence for continent locality and indicators of the environment throughout time. [4]

Phanerozoic (541 Ma to present) and Precambrian (4.6 Ga to 541 Ma) had primarily passive margins and detrital zircons (and orogenic granites), whereas the tenure of Pangaea contained few. [4] Matching edges of continents are where passive margins form. The edges of these continents may rift. At this point, seafloor spreading becomes the driving force. Passive margins are therefore born during the break-up of supercontinents and die during supercontinent assembly. Pangaea's supercontinent cycle is a good example of the efficiency of using the presence or lack of these entities to record the development, tenure, and break-up of supercontinents. There is a sharp decrease in passive margins between 500 and 350 Ma during the timing of Pangaea's assembly. The tenure of Pangaea is marked by a low number of passive margins during 336 to 275 Ma, and its break-up is indicated accurately by an increase in passive margins. [4]

Orogenic belts can form during the assembly of continents and supercontinents. The orogenic belts present on continental blocks are classified into three different categories and have implications for interpreting geologic bodies. [1] Intercratonic orogenic belts are characteristic of ocean basin closure. Clear indicators of intracratonic activity contain ophiolites and other oceanic materials that are present in the suture zone. Intracratonic orogenic belts occur as thrust belts and do not contain any oceanic material. However, the absence of ophiolites is not strong evidence for intracratonic belts, because the oceanic material can be squeezed out and eroded away in an intracratonic environment. The third kind of orogenic belt is a confined orogenic belt which is the closure of small basins. The assembly of a supercontinent would have to show intracratonic orogenic belts. [1] However, interpretation of orogenic belts can be difficult.

The collision of Gondwana and Laurasia occurred in the late Palaeozoic. By this collision, the Variscan mountain range was created, along the equator. [6] This 6000-km-long mountain range is usually referred to in two parts: the Hercynian mountain range of the late Carboniferous makes up the eastern part, and the western part is the Appalachian Mountains, uplifted in the early Permian. (The existence of a flat elevated plateau like the Tibetan Plateau is under debate.) The locality of the Variscan range made it influential to both the northern and southern hemispheres. The elevation of the Appalachians would greatly influence global atmospheric circulation. [6]

Climate

Continents affect the climate of the planet drastically, with supercontinents having a larger, more prevalent influence. Continents modify global wind patterns, control ocean current paths, and have a higher albedo than the oceans. [1] Winds are redirected by mountains, and albedo differences cause shifts in onshore winds. Higher elevation in continental interiors produces a cooler, drier climate, the phenomenon of continentality. This is seen today in Eurasia, and rock record shows evidence of continentality in the middle of Pangaea. [1]

Glacial

The term glacial-epoch refers to a long episode of glaciation on Earth over millions of years. [19] 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. [19] According to the model for Precambrian supercontinent series, the breakup of Kenorland and Rodinia was associated with the Paleoproterozoic and Neoproterozoic glacial epochs, respectively.

In contrast, the Protopangea–Paleopangea theory shows that these glaciations correlated with periods of low continental velocity, and it is concluded that a fall in tectonic and corresponding volcanic activity was responsible for these intervals of global frigidity. [11] During the accumulation of supercontinents with times of regional uplift, glacial epochs seem to be rare with little supporting evidence. However, the lack of evidence does not allow for the conclusion that glacial epochs are not associated with the collisional assembly of supercontinents. [19] This could just represent a preservation bias.

During the late Ordovician (~458.4 Ma), the particular configuration of Gondwana may have allowed for glaciation and high CO2 levels to occur at the same time. [20] 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 (~443.8 Ma) through the late Mississippian (~330.9 Ma). [6] Agreement can be met with the theory that continental snow can occur when the edge of a continent is near the pole. Therefore Gondwana, although located tangent to the South Pole, may have experienced glaciation along its coasts. [20]

Precipitation

Though precipitation rates during monsoonal circulations are difficult to predict, there is evidence for a large orographic barrier within the interior of Pangaea during the late Paleozoic (~251.9 Ma). The possibility of the southwest–northeast trending Appalachian-Hercynian Mountains makes the region's monsoonal circulations potentially relatable to present-day monsoonal circulations surrounding the Tibetan Plateau, which is known to positively influence the magnitude of monsoonal periods within Eurasia. It is therefore somewhat expected that lower topography in other regions of the supercontinent during the Jurassic would negatively influence precipitation variations. The breakup of supercontinents may have affected local precipitation. [21] 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 CO2. [9]

Temperature

Even though during the Archaean solar radiation was reduced by 30 percent and the Cambrian-Precambrian boundary by 6 percent, the Earth has only experienced three ice ages throughout the Precambrian. [6] Erroneous conclusions are more likely to be made when models are limited to one climatic configuration (which is usually present-day). [22]

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 CO2 content and ocean heat transport are not comparatively effective. [22]

CO2 models suggest that values were low in the late Cenozoic and Carboniferous-Permian glaciations. Although early Paleozoic values are much larger (more than 10 percent higher than that of today). This may be due to high seafloor spreading rates after the breakup of Precambrian supercontinents and the lack of land plants as a carbon sink. [20]

During the late Permian, it is expected that seasonal Pangaean temperatures varied drastically. Subtropic summer temperatures were warmer than that of today by as much as 6–10 degrees, and mid-latitudes in the winter were less than −30 degrees Celsius. These seasonal changes within the supercontinent were influenced by the large size of Pangaea. And, just like today, coastal regions experienced much less variation. [6]

During the Jurassic, summer temperatures did not rise above zero degrees Celsius along the northern rim of Laurasia, which was the northernmost part of Pangaea (the southernmost portion of Pangaea was Gondwana). Ice-rafted dropstones sourced from Russia are indicators of this northern boundary. The Jurassic is thought to have been approximately 10 degrees Celsius warmer along 90 degrees East paleolongitude compared to the present temperature of today's central Eurasia. [22]

Milankovitch cycles

Many studies of the Milankovitch cycles during supercontinent time periods have focused on the mid-Cretaceous. Present amplitudes of Milankovitch cycles over present-day Eurasia may be mirrored in both the southern and northern hemispheres of the supercontinent Pangaea. Climate modeling shows that summer fluctuations varied 14–16 degrees Celsius on Pangaea, which is similar or slightly higher than summer temperatures of Eurasia during the Pleistocene. The largest-amplitude Milankovitch cycles are expected to have been at mid-to high-latitudes during the Triassic and Jurassic. [22]

Atmospheric gases

Plate tectonics and the chemical composition of the atmosphere (specifically greenhouse gases) are the two most prevailing factors present within the geologic time scale. Continental drift influences both cold and warm climatic episodes. Atmospheric circulation and climate are strongly influenced by the location and formation of continents and supercontinents. Therefore, continental drift influences mean global temperature. [6]

Oxygen levels of the Archaean were negligible, and today they are roughly 21 percent. It is thought that the Earth's oxygen content has risen in stages: six or seven steps that are timed very closely to the development of Earth's supercontinents. [23]

  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. [23]

At 2.65 Ga there was an increase in molybdenum isotope fractionation. It was temporary but supports the increase in atmospheric oxygen because molybdenum isotopes require free oxygen to fractionate. Between 2.45 and 2.32 Ga, the second period of oxygenation occurred, which has been called the 'great oxygenation event.' Evidence supporting this event includes red beds appearance 2.3 Ga (meaning that Fe3+ was being produced and became an important component in soils).

The third oxygenation stage approximately 1.8 Ga is indicated by the disappearance of iron formations. Neodymium isotopic studies suggest that iron formations are usually from continental sources, meaning that dissolved Fe and Fe2+ had to be transported during continental erosion. A rise in atmospheric oxygen prevents Fe transport, so the lack of iron formations may have been the result of an increase in oxygen. The fourth oxygenation event, roughly 0.6 Ga, is based on modeled rates of sulfur isotopes from marine carbonate-associated sulfates. An increase (near doubled concentration) of sulfur isotopes, which is suggested by these models, would require an increase in the oxygen content of the deep oceans.

Between 650 and 550 Ma there were three increases in ocean oxygen levels, this period is the fifth oxygenation stage. One of the reasons indicating this period to be an oxygenation event is the increase in redox-sensitive molybdenum in black shales. The sixth event occurred between 360 and 260 Ma and was identified by models suggesting shifts in the balance of 34S in sulfates and 13C in carbonates, which were strongly influenced by an increase in atmospheric oxygen. [23] [24]

Proxies

U-Pb ages of 5,246 concordant detrital zircons from 40 of Earth's major rivers FigureUPbZircons.jpg
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. [4] Oceanic magnetic anomalies and paleomagnetic data are the primary resources used for reconstructing continent and supercontinent locations back to roughly 150 Ma. [6]

See also

Related Research Articles

The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.

Rodinia was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago (Ga) and broke up 750–633 million years ago (Ma). Valentine & Moores 1970 were probably the first to recognise a Precambrian supercontinent, which they named "Pangaea I." It was renamed "Rodinia" by McMenamin & McMenamin 1990 who also were the first to produce a reconstruction and propose a temporal framework for the supercontinent.

<span class="mw-page-title-main">Proterozoic</span> Geologic eon, 2500–539 million years ago

The Proterozoic is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, the longest eon of the Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozoic, and is the most recent part of the Precambrian "supereon".

<span class="mw-page-title-main">Laurasia</span> Northern landmass that formed part of the Pangaea supercontinent

Laurasia was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around 335 to 175 million years ago (Mya), the other being Gondwana. It separated from Gondwana 215 to 175 Mya during the breakup of Pangaea, drifting farther north after the split and finally broke apart with the opening of the North Atlantic Ocean c. 56 Mya. The name is a portmanteau of Laurentia and Asia.

<span class="mw-page-title-main">Kenorland</span> Hypothetical Neoarchaean supercontinent from about 2.8 billion years ago

Kenorland was one of the earliest known supercontinents on Earth. It is thought to have formed during the Neoarchaean Era c. 2.72 billion years ago by the accretion of Neoarchaean cratons and the formation of new continental crust. It comprised what later became Laurentia, Baltica, Western Australia and Kalaharia.

<span class="mw-page-title-main">Arctica</span> Ancient continent in the Neoarchean era

Arctica, or Arctida was an ancient continent which formed approximately 2.565 billion years ago in the Neoarchean era. It was made of Archaean cratons, including the Siberian Craton, with its Anabar/Aldan shields in Siberia, and the Slave, Wyoming, Superior, and North Atlantic cratons in North America. Arctica was named by Rogers 1996 because the Arctic Ocean formed by the separation of the North American and Siberian cratons. Russian geologists writing in English call the continent "Arctida" since it was given that name in 1987, alternatively the Hyperborean craton, in reference to the hyperboreans in Greek mythology.

<span class="mw-page-title-main">Pannotia</span> Hypothesized Neoproterozoic supercontinent

Pannotia, also known as the Vendian supercontinent, Greater Gondwana, and the Pan-African supercontinent, was a relatively short-lived Neoproterozoic supercontinent that formed at the end of the Precambrian during the Pan-African orogeny, during the Cryogenian period and broke apart 560 Ma with the opening of the Iapetus Ocean, in the late Ediacaran and early Cambrian. Pannotia formed when Laurentia was located adjacent to the two major South American cratons, Amazonia and Río de la Plata. The opening of the Iapetus Ocean separated Laurentia from Baltica, Amazonia, and Río de la Plata. A 2022 paper argues that Pannotia never fully existed, reinterpreting the geochronological evidence: "the supposed landmass had begun to break up well before it was fully assembled". However, the assembly of the next supercontinent Pangaea is well established.

<span class="mw-page-title-main">Neoarchean</span> Fourth era of the Archean Eon

The Neoarchean is the last geologic era in the Archean Eon that spans from 2800 to 2500 million years ago—the period being defined chronometrically and not referencing a specific level in a rock section on Earth. The era is marked by major developments in complex life and continental formation.

<span class="mw-page-title-main">Supercontinent cycle</span> Theory Earths continental crust movement

The supercontinent cycle is 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 reconfigured. One complete supercontinent cycle is said to take 300 to 500 million years. Continental collision makes fewer and larger continents while rifting makes more and smaller continents.

The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.

<span class="mw-page-title-main">Geological history of Earth</span> The sequence of major geological events in Earths past

The geological history of the Earth follows the major geological events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.

<span class="mw-page-title-main">Ur (continent)</span> Hypothetical Archaean supercontinent from about 3.1 billion years ago

Ur is a hypothetical supercontinent that formed in the Archean eon around 3.1 billion years ago (Ga). In a reconstruction by Rogers, Ur is half a billion years older than Arctica and, in the early period of its existence, probably the only continent on Earth, making it a supercontinent despite probably being smaller than present-day Australia. In more recent works geologists often refer to both Ur and other proposed Archaean continental assemblages as supercratons. Ur can, nevertheless, be half a billion years younger than Vaalbara, but the concepts of these two early cratonic assemblages are incompatible.

<span class="mw-page-title-main">Laurentia</span> Craton forming the geological core of North America

Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although originally it also included the cratonic areas of Greenland and also the northwestern part of Scotland, known as the Hebridean Terrane. During other times in its past, Laurentia has been part of larger continents and supercontinents and consists of many smaller terranes assembled on a network of early Proterozoic orogenic belts. Small microcontinents and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable Precambrian craton seen today.

<span class="mw-page-title-main">Pangaea</span> Supercontinent from the late Paleozoic to early Mesozoic eras

Pangaea or Pangea was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million years ago, and began to break apart about 200 million years ago, at the end of the Triassic and beginning of the Jurassic. In contrast to the present Earth and its distribution of continental mass, Pangaea was C-shaped, with the bulk of its mass stretching between Earth's northern and southern polar regions 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.

This is a list of articles related to plate tectonics and tectonic plates.

A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes, some are just a collection of small microcontinents while others are large conglomerates of crust. As time progresses and sea levels rise and fall more crust can be exposed making way for larger landmasses. The continents of the past shaped the evolution of organisms on Earth and contributed to the climate of the globe as well. As landmasses break apart, species are separated and those that were once the same now have evolved to their new climate. The constant movement of these landmasses greatly determines the distribution of organisms on Earth's surface. This is evident with how similar fossils are found on completely separate continents. Also, as continents move, mountain building events (orogenies) occur, causing a shift in the global climate as new rock is exposed and then there is more exposed rock at higher elevations. This causes glacial ice expansion and an overall cooler global climate. The movement of the continents greatly affects the overall dispersal of organisms throughout the world and the trend in climate throughout Earth's history. Examples include Laurentia, Baltica and Avalonia, which collided together during the Caledonian orogeny to form the Old Red Sandstone paleocontinent of Laurussia. Another example includes a collision that occurred during the late Pennsylvanian and early Permian time when there was a collision between the two continents of Tarimsky and Kirghiz-Kazakh. This collision was caused because of their askew convergence when the paleoceanic basin closed.

<span class="mw-page-title-main">Tectonic evolution of the Aravalli Mountains</span> Overview article

The Aravalli Mountain Range is a northeast-southwest trending orogenic belt in the northwest part of India and is part of the Indian Shield that was formed from a series of cratonic collisions. The Aravalli Mountains consist of the Aravalli and Delhi fold belts, and are collectively known as the Aravalli-Delhi orogenic belt. The whole mountain range is about 700 km long. Unlike the much younger Himalayan section nearby, the Aravalli Mountains are believed much older and can be traced back to the Proterozoic Eon. They are arguably the oldest geological feature on Earth. The collision between the Bundelkhand craton and the Marwar craton is believed to be the primary mechanism for the development of the mountain range.

<span class="mw-page-title-main">Qinling orogenic belt</span>

The Qinling orogenic belt is a tectonic feature that evolved throughout the Proterozoic and Phanerozoic eons due to a variety of tectonic activities. It is a part of the Central China Orogenic Belt, aligned in an east–west orientation across Central China, and spans portions of Shaanxi, Henan and Gansu provinces along the Qinling Mountains which are one of the greatest mountain ranges in China. The first materials involved in the Qinling orogenic belt formed around 2.5 billion years ago, whereas the main morphology of the belt now largely reflects the Triassic collision between the North China Plate and the South China Plate and Cenozoic extension across China. During these 2.5 billion years, various types of rocks have been formed here due to different tectonic processes and chemical reactions between rocks. Therefore, geologists are able to reconstruct the evolution of mountain belt based on evidence preserved in these rocks.

<span class="mw-page-title-main">South China Craton</span> Precambrian continental block located in China

The South China Craton or South China Block is one of the Precambrian continental blocks in China. It is traditionally divided into the Yangtze Block in the NW and the Cathaysia Block in the SE. The Jiangshan–Shaoxing Fault represents the suture boundary between the two sub-blocks. Recent study suggests that the South China Block possibly has one more sub-block which is named the Tolo Terrane. The oldest rocks in the South China Block occur within the Kongling Complex, which yields zircon U–Pb ages of 3.3–2.9 Ga.

A continent is a large geographical region defined by the continental shelves and the cultures on the continent. In the modern day, there are seven continents. However, there have been more continents throughout history. Vaalbara was the first supercontinent. Europe is the newest continent. Geologists have predicted that certain continents will appear, these being Pangaea Proxima, Novopangaea, Aurica, and Amasia.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 Rogers, John J. W.; Santosh, M. (2004). Continents and supercontinents. New York: Oxford University Press. ISBN   978-0195165890 . Retrieved 5 January 2021.
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  3. ↑ Hoffman, P.F. (1999). "The break-up of Rodinia, birth of Gondwana, true polar wander and the snowball Earth". Journal of African Earth Sciences. 28 (1): 17–33. Bibcode:1999JAfES..28...17H. doi:10.1016/S0899-5362(99)00018-4.
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  5. ↑ Meert, J.G. (2012). "What's in a name? The Columbia (Paleopangaea/Nuna) supercontinent". Gondwana Research. 21 (4): 987–993. Bibcode:2012GondR..21..987M. doi:10.1016/j.gr.2011.12.002.
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  7. 1 2 Bradley, D. C. (23 December 2014). "Mineral evolution and Earth history". American Mineralogist. 100 (1): 4–5. Bibcode:2015AmMin.100....4B. doi:10.2138/am-2015-5101. S2CID   140191182.
  8. ↑ Williams, Caroline; Nield, Ted (October 2007). "Earth's next supercontinent". New Scientist. 196 (2626): 36–40. doi:10.1016/S0262-4079(07)62661-X.
  9. 1 2 Donnadieu, Yannick et al. "A 'Snowball Earth' Climate Triggered by Continental Break-Up Through Changes in Runoff." Nature, 428 (2004): 303–306.
  10. ↑ Piper, J.D.A. "A planetary perspective on Earth evolution: Lid Tectonics before Plate Tectonics." Tectonophysics. 589 (2013): 44–56.
  11. 1 2 3 Piper, J.D.A. "Continental velocity through geological time: the link to magmatism, crustal accretion and episodes of global cooling." Geoscience Frontiers. 4 (2013): 7–36.
  12. ↑ Z.X, Li (October 2009). "How not to build a supercontinent: A reply to J.D.A. Piper". Precambrian Research. 174 (1–2): 208–214. Bibcode:2009PreR..174..208L. doi:10.1016/j.precamres.2009.06.007.
  13. ↑ de Kock, M.O.; Evans, D.A.D.; Beukes, N.J. (2009). "Validating the existence of Vaalbara in the Neoarchean" (PDF). Precambrian Research. 174 (1–2): 145–154. Bibcode:2009PreR..174..145D. doi:10.1016/j.precamres.2009.07.002.
  14. ↑ Mahapatro, S.N.; Pant, N.C.; Bhowmik, S.K.; Tripathy, A.K.; Nanda, J.K. (2011). "Archaean granulite facies metamorphism at the Singhbhum Craton–Eastern Ghats Mobile Belt interface: implication for the Ur supercontinent assembly". Geological Journal. 47 (2–3): 312–333. doi: 10.1002/gj.1311 . S2CID   127300220.
  15. 1 2 3 4 Nance, R.D.; Murphy, J.B.; Santosh, M. (2014). "The supercontinent cycle: A retrospective essay". Gondwana Research. 25 (1): 4–29. Bibcode:2014GondR..25....4N. doi:10.1016/j.gr.2012.12.026.
  16. ↑ Evans, D.A.D. (2013). "Reconstructing pre-Pangean supercontinents" (PDF). GSA Bulletin. 125 (11–12): 1736. Bibcode:2013GSAB..125.1735E. doi:10.1130/B30950.1.
  17. ↑ Piper, J.D.A. "Protopangea: palaeomagnetic definition of Earth's oldest (Mid-Archaean-Paleoproterozoic) supercontinent." Journal of Geodynamics. 50 (2010): 154–165.
  18. ↑ Piper, J.D.A., "Paleopangea in Meso-Neoproterozoic times: the paleomagnetic evidence and implications to continental integrity, supercontinent from and Eocambrian break-up." Journal of Geodynamics. 50 (2010): 191–223.
  19. 1 2 3 Eyles, Nick. "Glacio-epochs and the Supercontinent Cycle after ~3.0 Ga: Tectonic Boundary Conditions for Glaciation." Paleogeography, Palaeoclimatology, Palaeoecology 258 (2008): 89–129. Print.
  20. 1 2 3 Crowley, Thomas J., "Climate Change on Tectonic Time Scales". Tectonophysics. 222 (1993): 277–294.
  21. ↑ Baum, Steven K., and Thomas J. Crowley. "Milankovitch Fluctuations on Supercontinents." Geophysical Research Letters. 19 (1992): 793–796. Print.
  22. 1 2 3 4 Baum, Steven K., and Thomas J. Crowely. "Milankovitch Fluctuations on Supercontinents." Geophysical Research Letters. 19 (1992): 793–796. Print.
  23. 1 2 3 4 Campbell, Ian H., Charlotte M. Allen. "Formation of Supercontinents Linked to Increases in Atmospheric Oxygen." Nature. 1 (2008): 554–558.
  24. ↑ "G'day mate: 1.7-billion-year-old chunk of North America found in Australia". www.msn.com. Archived from the original on 2018-01-25.

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