Editing Supercontinent

{{Short description|Landmass comprising more than one continental core, or craton}}
[[File:Pangea assembly 250.png|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 craton|North China]]; SC=[[South China craton|South China]]; PA=[[Panthalassic Ocean]]; PT=[[Paleotethys Ocean]]; NT=[[Neotethys Ocean]]. [[Orogen]]s shown in red. [[Subduction zone]]s shown in black. [[Spreading center]]s shown in green.]]
[[File:Afro-Eurasia.png|thumb|Although not a supercontinent, the current [[Afro-Eurasia]]n landmass contains about 57% of Earth's land area.]]

In [[geology]], a '''supercontinent''' is the assembly of most or all of [[Earth]]'s [[continent|continental blocks]] or [[craton]]s to form a single large landmass.<ref name="rogers">{{cite book |last1=Rogers |first1=John J. W. |last2=Santosh |first2=M. |title=Continents and supercontinents |date=2004 |publisher=Oxford University Press |location=New York |isbn=978-0195165890 |url=https://books.google.com/books?id=CI9Ig7DGvTMC&q=Rogers%2C+John+J.+W.%2C+and+M.+Santosh.+Continents+and+Supercontinents.+Oxford++Oxford+UP%2C+2004.+Print.&pg=PP1 |access-date=5 January 2021}}</ref><ref name="Rogers_&_Santosh_2002">{{Cite journal |last1=Rogers |first1=J.J.W. |last2=Santosh |first2=M. |date=2002 |title=Configuration of Columbia, a Mesoproterozoic Supercontinent |url=http://szczepan.ct8.pl/teksty/seminar/3.pdf |url-status=dead |journal=Gondwana Research |volume=5 |issue=1 |pages=5–22 |doi=10.1016/S1342-937X(05)70883-2 |bibcode=2002GondR...5....5R |archive-url=https://web.archive.org/web/20150203145852/http://szczepan.ct8.pl/teksty/seminar/3.pdf |archive-date=2015-02-03}}</ref><ref name="hoffman">{{Cite journal |last=Hoffman |first=P.F. |year=1999 |title=The break-up of Rodinia, birth of Gondwana, true polar wander and the snowball Earth |journal=Journal of African Earth Sciences |volume=28 |issue=1 |pages=17–33 |doi=10.1016/S0899-5362(99)00018-4|bibcode=1999JAfES..28...17H }}</ref> 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.<ref name="bradley">{{Cite journal |last=Bradley |first=D.C. |date=2011 |title=Secular Trends in the Geologic Record and the Supercontinent Cycle |journal=Earth-Science Reviews |volume=108 |issue=1–2 |pages=16–33 |doi=10.1016/j.earscirev.2011.05.003|bibcode=2011ESRv..108...16B |citeseerx=10.1.1.715.6618 |s2cid=140601854 }}</ref> 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.<ref name="Meert_2012">{{Cite journal |last=Meert |first=J.G. |year=2012 |title=What's in a name? The Columbia (Paleopangaea/Nuna) supercontinent |journal=Gondwana Research |volume=21 |issue=4 |pages=987–993 |doi=10.1016/j.gr.2011.12.002|bibcode=2012GondR..21..987M }}</ref>

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;<ref name="rogers"/> the closest  is the current [[Afro-Eurasia]]n 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.<ref name="flutaeu">Fluteau, Frédéric. (2003). "Earth dynamics and climate changes". C. R. Geoscience '''335''' (1): 157–174. doi:10.1016/S1631-0713(03)00004-X</ref> Pangaea's predecessor [[Gondwana]] is not considered a supercontinent under the first definition since the landmasses of [[Baltica]], [[Laurentia]] and [[Siberia (continent)|Siberia]] were separate at the time.<ref name=Bradley>{{cite journal|last1=Bradley|first1=D. C.|title=Mineral evolution and Earth history|journal=American Mineralogist|date=23 December 2014|volume=100|issue=1|pages=4–5|doi=10.2138/am-2015-5101|bibcode=2015AmMin.100....4B|s2cid=140191182}}</ref>

A future supercontinent, termed [[Pangaea Proxima]], is hypothesized to form within the next 250 million years.<ref name="WilliamsNield2007">{{cite journal |last1=Williams |first1=Caroline |last2=Nield |first2=Ted |title=Earth's next supercontinent |journal=New Scientist |date=October 2007 |volume=196 |issue=2626 |pages=36–40 |doi=10.1016/S0262-4079(07)62661-X }}</ref>

== Theories ==
The [[Phanerozoic]] supercontinent Pangaea began to break up {{nobr|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.<ref name="bradley" />

For the period before Pangaea, there are two contrasting models for supercontinent evolution through [[Geologic time scale|geological time]]. 

=== Series ===
The first model theorizes that at least two separate supercontinents existed comprising [[Vaalbara]] and [[Kenorland]], with Kenorland comprising [[Superior craton|Superia]] and [[Sclavia craton|Sclavia]]. These parts of [[Neoarchean]] age broke off at ~2480 and {{nobr|2312 Ma}}, and portions of them later collided to form [[Columbia (supercontinent)|Nuna]] (Northern Europe and North America). Nuna continued to develop during the [[Mesoproterozoic]], primarily by lateral [[Accretion (geology)|accretion]] of juvenile arcs, and in {{nobr|~1000 Ma}} Nuna collided with other land masses, forming [[Rodinia]].<ref name="bradley" /> Between ~825 and {{nobr|750 Ma}} Rodinia broke apart.<ref name="donnadieu">Donnadieu, Yannick et al. "A 'Snowball Earth' Climate Triggered by Continental Break-Up Through Changes in Runoff." Nature, 428 (2004): 303–306.</ref> However, before completely breaking up, some fragments of Rodinia had already come together to form [[Gondwana]] by {{nobr|~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 [[Paleomagnetism|palaeomagnetic]] and geological evidence and proposes that the continental crust comprised a single supercontinent from {{nobr|~2.72 Ga}} until break-up during the [[Ediacaran]] period after {{nobr|~0.573 Ga}}. The [[plate reconstruction|reconstruction]]<ref name="piper1">Piper, J.D.A. "A planetary perspective on Earth evolution: Lid Tectonics before Plate Tectonics." Tectonophysics. 589 (2013): 44–56.</ref> 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 {{nobr|0.75–0.573 Ga}} with only small peripheral modifications to the reconstruction.<ref name="piper2">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.</ref> 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.<ref name="piper2" /> This approach was widely criticized by many researchers as it uses incorrect application of paleomagnetic data.<ref name="li2009">{{cite journal |last1=Z.X |first1=Li |date=October 2009 |title=How not to build a supercontinent: A reply to J.D.A. Piper |journal=Precambrian Research |volume=174 |issue=1–2 |pages=208–214 |bibcode=2009PreR..174..208L |doi=10.1016/j.precamres.2009.06.007}}</ref>

== Cycles ==
A [[supercontinent cycle]] is the break-up of one supercontinent and the development of another, which takes place on a global scale.<ref name="bradley" /> 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.<ref name="rogers" /> However, supercontinent cycles and Wilson cycles were both involved in the creation of Pangaea and Rodinia.<ref name="flutaeu" />

[[Secular variation|Secular]] trends such as [[carbonatite]]s, [[granulite]]s, [[eclogite]]s, 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.<ref name="bradley" />

The following table names reconstructed ancient supercontinents, using Bradley's 2011 looser definition,<ref name="Bradley" /> with an approximate timescale of millions of years ago (Ma).

{| class="wikitable"
! Supercontinent name !! Age (Ma) || Period/Era Range || Comment
|-
|[[Vaalbara]]
|3,636–2,803 || Eoarchean-Mesoarchean ||Also described as a supercraton or just a continent<ref name="de_Kock__etal_2009">{{Cite journal |last1=de Kock |first1=M.O. |last2=Evans |first2=D.A.D. |last3=Beukes |first3=N.J. |date=2009 |title=Validating the existence of Vaalbara in the Neoarchean |url=https://people.earth.yale.edu/sites/default/files/files/Evans/35_09g-deKock+Vaalbara.pdf |journal=Precambrian Research |volume=174 |issue=1–2 |pages=145–154 |doi=10.1016/j.precamres.2009.07.002|bibcode=2009PreR..174..145D }}</ref>
|-
| [[Ur (continent)|Ur]] || 2,803–2,408 || Mesoarchean-Siderian ||Described as both a continent<ref name="Rogers_&_Santosh_2002"/> and a supercontinent<ref name="Mahapatro_etal_2011">{{Cite journal |last1=Mahapatro |first1=S.N. |last2=Pant |first2=N.C. |last3=Bhowmik |first3=S.K. |last4=Tripathy |first4=A.K. |last5=Nanda |first5=J.K. |date=2011 |title=Archaean granulite facies metamorphism at the Singhbhum Craton–Eastern Ghats Mobile Belt interface: implication for the Ur supercontinent assembly |url=https://www.academia.edu/26707795|journal=Geological Journal |volume=47 |issue=2–3 |pages=312–333 |doi=10.1002/gj.1311|s2cid=127300220 |doi-access=free }}</ref>
|-
| [[Kenorland]] || 2,720–2,114 || Neoarchean-Rhyacian ||Alternatively the continents may have formed into two groupings [[Superior craton|Superia]] and [[Sclavia craton|Sclavia]]<ref name="Nance_etal_2014">{{Cite journal |last1=Nance |first1=R.D. |last2=Murphy |first2=J.B. |last3=Santosh |first3=M. |date=2014 |title=The supercontinent cycle: A retrospective essay |journal=Gondwana Research |volume=25 |issue=1 |pages=4–29 |doi=10.1016/j.gr.2012.12.026|bibcode=2014GondR..25....4N }}</ref><ref name="bradley" />
|-
| [[Arctica]] || 2,114–1,995 || Rhyacian-Orosirian ||Not generally regarded as a supercontinent, depending on definition<ref name="Rogers_&_Santosh_2002"/>
|-
|[[Atlantica]]
|1,991–1,124 || Orosirian-Stenian ||Not generally regarded as a supercontinent, depending on definition<ref name="Rogers_&_Santosh_2002"/>
|-
| [[Columbia (supercontinent)|Columbia (Nuna)]] || 1,820–1,350 || Orosirian-Ectasian ||<ref name="Nance_etal_2014"/>
|-
| [[Rodinia]] || 1,130–750 || Stenian-Tonian ||<ref name="Nance_etal_2014"/>
|-
| [[Pannotia]] || 633–573 || Ediacaran ||<ref name="Nance_etal_2014"/>
|- 
|[[Gondwana]] || 550–175 || Ediacaran-Jurassic ||From the Carboniferous, formed part of Pangaea,<ref name="bradley" /> not always regarded as a supercontinent<ref name="Evans_2013">{{Cite journal |last=Evans |first=D.A.D. |date=2013 |title=Reconstructing pre-Pangean supercontinents
|url=https://people.earth.yale.edu/sites/default/files/files/Evans/58-GSAB125.pdf |journal=GSA Bulletin |volume=125 |issue=11–12 |pages=1736 |doi=10.1130/B30950.1|bibcode=2013GSAB..125.1735E }}</ref>
|-
| [[Pangaea]] || 336–175 || Carboniferous-Jurassic ||
|}

==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<ref name=rogers />]] -->
<!-- Deleted image removed: [[File:FigureSupercontinentBreakup.jpg|thumb|The effects of mantle plumes possibly caused by slab avalanches elsewhere in the lower mantle on the breakup and assembly of supercontinents<ref name=rogers />]] -->

The causes of supercontinent assembly and dispersal are thought to be driven by [[convection]] processes in [[Earth's mantle]]. Approximately 660&nbsp;km into the mantle, a discontinuity occurs, affecting the [[Earth's crust|surface crust]] through processes involving [[mantle plume|plumes]] and ''superplumes'' (aka [[large low-shear-velocity provinces]]). When a slab of the [[Subduction|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.<ref name=rogers />

Besides having compositional effects on the [[upper mantle]] by replenishing the [[incompatible element|large-ion lithophile elements]], volcanism affects plate movement.<ref name=rogers /> 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.<ref name='piper3'>Piper, J.D.A. "Protopangea: palaeomagnetic definition of Earth's oldest (Mid-Archaean-Paleoproterozoic) supercontinent." Journal of Geodynamics. 50 (2010): 154–165.</ref> 

Dispersal of supercontinents is caused by the accumulation of heat underneath the crust due to the rising of very large [[convection cell]]s or plumes, and a massive heat release resulted in the final break-up of Paleopangea.<ref name="piper4">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.</ref> 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 basalt]]s. 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 [[paleoclimatology|paleoclimate]].<ref name=flutaeu />

==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 belt]]s, 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.<ref name=bradley />

Phanerozoic (541 Ma to present) and Precambrian ({{nobr|4.6 Ga}} to {{nobr|541 Ma}}) had primarily passive margins and detrital [[zircon]]s (and orogenic [[granite]]s), whereas the tenure of Pangaea contained few.<ref name=bradley /> 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 {{nobr|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 {{nobr|275 Ma,}} and its break-up is indicated accurately by an increase in passive margins.<ref name=bradley />

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.<ref name=rogers /> Intercratonic orogenic belts are characteristic of ocean basin closure. Clear indicators of intracratonic activity contain [[ophiolite]]s 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.<ref name=rogers /> However, interpretation of orogenic belts can be difficult.

The collision of Gondwana and Laurasia occurred in the late Palaeozoic. By this collision, the [[Variscan orogeny|Variscan mountain range]] was created, along the equator.<ref name=flutaeu /> This 6000-km-long mountain range is usually referred to in two parts: the [[Variscan orogeny|Hercynian mountain range]] of the late Carboniferous makes up the eastern part, and the western part is the [[Appalachian Mountains]], uplifted in the [[Cisuralian|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.<ref name=flutaeu />

==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.<ref name=rogers /> 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 [[Continental climate|continentality]]. This is seen today in [[Eurasia]], and rock record shows evidence of continentality in the middle of Pangaea.<ref name=rogers />

===Glacial===

The term glacial-epoch refers to a long episode of [[Glacial period|glaciation]] on Earth over millions of years.<ref name='eyles'>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.</ref> 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.<ref name=eyles /> 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.<ref name="piper2" /> 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.<ref name="eyles" /> 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 CO<sub>2</sub> levels to occur at the same time.<ref name="crowley">Crowley, Thomas J., "Climate Change on Tectonic Time Scales". Tectonophysics. 222 (1993): 277–294.</ref> 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 [[Llandovery epoch|early Silurian]] {{nobr|(~443.8 Ma)}} through the late [[Mississippian age|Mississippian]] {{nobr|(~330.9 Ma).}}<ref name="flutaeu" /> 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.<ref name="crowley" />

===Precipitation===

Though precipitation rates during [[Monsoon|monsoonal]] circulations are difficult to predict, there is evidence for a large orographic barrier within the interior of Pangaea during the late Paleozoic {{nobr|(~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.<ref name="Baum">Baum, Steven K., and Thomas J. Crowley. "Milankovitch Fluctuations on Supercontinents." Geophysical Research Letters. 19 (1992): 793–796. Print.</ref> When any supercontinent breaks up, there will be an increase in precipitation [[Surface runoff|runoff]] over the surface of the continental landmasses, increasing [[Silicate mineral|silicate]] [[weathering]] and the consumption of CO<sub>2</sub>.<ref name=donnadieu />

===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 age|ice ages]] throughout the Precambrian.<ref name=flutaeu /> Erroneous conclusions are more likely to be made when models are limited to one climatic configuration (which is usually present-day).<ref name="baum">Baum, Steven K., and Thomas J. Crowely. "Milankovitch Fluctuations on Supercontinents." Geophysical Research Letters. 19 (1992): 793–796. Print.</ref>

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.<ref name=baum />

CO<sub>2</sub> 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]].<ref name=crowley />

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.<ref name=flutaeu />

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 [[dropstone]]s 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 [[paleomagnetism|paleolongitude]] compared to the present temperature of today's central Eurasia.<ref name=baum />

===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.<ref name=baum />

=== Atmospheric gases ===
[[Plate tectonics]] and the chemical composition of the atmosphere (specifically [[greenhouse gas]]es) 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.<ref name="flutaeu" />

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.<ref name="Campbell">Campbell, Ian H., Charlotte M. Allen. "Formation of Supercontinents Linked to Increases in Atmospheric Oxygen." Nature. 1 (2008): 554–558.</ref>
# Continents collide
# Super-mountains form
# Erosion of super-mountains
# Large quantities of minerals and nutrients wash out to open ocean
# Explosion of marine algae life (partly sourced from noted nutrients)
# 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.<ref name="Campbell" />

At {{nobr|2.65 Ga}} there was an increase in [[Isotopes of molybdenum|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 {{nobr|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 {{nobr|2.3 Ga}} (meaning that Fe<sup>3+</sup> was being produced and became an important component in soils). 

The third oxygenation stage approximately {{nobr|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 Fe<sup>2+</sup> 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 {{nobr|0.6 Ga,}} is based on modeled rates of [[Isotopes of sulfur|sulfur isotopes]] from marine carbonate-associated [[sulfate]]s. 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 {{nobr|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 [[shale]]s. The sixth event occurred between 360 and {{nobr|260 Ma}} and was identified by models suggesting shifts in the balance of <sup>34</sup>S in [[sulfate]]s and <sup>13</sup>C in [[carbonate]]s, which were strongly influenced by an increase in atmospheric oxygen.<ref name="Campbell" /><ref>{{cite web |title=G'day mate: 1.7-billion-year-old chunk of North America found in Australia |url=https://www.MSN.com/en-us/news/technology/day-mate-17-billion-year-old-chunk-of-north-America-found-in-Australia/ar-AAv5aZn |url-status=live |archive-url=https://web.archive.org/web/20180125134510/http://www.msn.com/en-us/news/technology/gday-mate-17-billion-year-old-chunk-of-north-america-found-in-australia/ar-AAv5aZn |archive-date=2018-01-25 |website=www.msn.com}}</ref>

==Proxies==
<!-- Deleted image removed: [[File:FigureUPbZircons.jpg|thumb|U–Pb ages of 5,246 concordant detrital zircons from 40 of Earth's major rivers<ref name="Campbell">Campbell, Ian H., Charlotte M. Allen. "Formation of Supercontinents Linked to Increases in Atmospheric Oxygen." Nature. 1 (2008): 554–558.</ref>]] -->

Granites and detrital zircons have notably similar and episodic appearances in the rock record. Their fluctuations correlate with Precambrian supercontinent cycles. The [[Uranium–lead dating|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 [[pluton]]ic consumption. Where granite zircons are less adequate, detrital zircons from [[sandstone]]s appear and make up for the gaps. These detrital zircons are taken from the sands of major modern rivers and their [[drainage basin]]s.<ref name="bradley" /> Oceanic magnetic anomalies and paleomagnetic data are the primary resources used for reconstructing continent and supercontinent locations back to roughly 150 Ma.<ref name="flutaeu" />

== See also ==
* [[List of paleocontinents]]
* [[Superocean]]

==References==
{{Reflist}}

==Further reading==
* Nield, Ted, ''Supercontinent: Ten Billion Years in the Life of Our Planet'', Harvard University Press, 2009, {{ISBN|978-0674032453}}

==External links==
* [http://scotese.com/ The Paleomap Project – Christopher R. Scotese]
{{Continents of the world}}

[[Category:Continents|*]]
[[Category:Historical geology]]
[[Category:Supercontinents| ]]