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69-649: Archaeagnostinae, Quadragnostinae The Peronopsidae (which may also be called peronopsids ) comprise the earliest family of the Agnostina suborder. Species of this family occurred on all paleocontinents . The earliest representatives of this family first occur just before the start of the Middle Cambrian , and the last disappeared just after the start of the Upper Cambrian . Peronopsidae are cosmopolitan . Temporal distribution: The Peronopsidae are considered to be

138-532: A preservation bias . During the late Ordovician (~458.4 Ma), the particular configuration of Gondwana may have allowed for glaciation and high CO 2 levels to occur at the same time. 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

207-550: A low number of passive margins during 336 to 275 Ma, and its break-up is indicated accurately by an increase in passive margins. 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. Intercratonic orogenic belts are characteristic of ocean basin closure. Clear indicators of intracratonic activity contain ophiolites and other oceanic materials that are present in

276-578: A single lava flow is also undetermined. These are important factors on how flood basalts influenced paleoclimate . 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

345-401: 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. Besides having compositional effects on

414-519: A supercontinent would have to show intracratonic orogenic belts. 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. This 6000-km-long mountain range is usually referred to in two parts: the Hercynian mountain range of the late Carboniferous makes up

483-694: Is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia , or Europe north of the Trans-European Suture Zone and west of the Ural Mountains . The thick core of Baltica, the East European Craton , is more than three billion years old and formed part of the Rodinia supercontinent at c. 1  Ga . Baltica formed at c. 2.0–1.7 Ga by

552-503: Is an association between the rifting and breakup of continents and supercontinents and glacial epochs. 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

621-498: 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 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

690-453: Is better preserved south of the polar region (65 °N) where shallow-water sediments can be found in the western Urals whilst the eastern Urals are characterised by deep-water deposits. The oldest known mid-ocean hydrothermal vent in the south-central part of the Urals clearly delimits the eastern extent. The straightness of the mountain chain is the result of continuous strike-slip movements during

759-448: Is concluded that a fall in tectonic and corresponding volcanic activity was responsible for these intervals of global frigidity. 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. This could just represent

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828-534: 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

897-413: Is hypothesized to form within the next 250 million years. 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

966-472: Is seen today in Eurasia , and rock record shows evidence of continentality in the middle of Pangaea. The term glacial-epoch refers to a long episode of glaciation on Earth over millions of years. 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

1035-943: Is the Timanide orogen which stretches north to the Novaya Zemlya archipelago. The extent of the Proterozoic continent are defined by the Iapetus Suture to the west; the Trollfjorden-Komagelva Fault Zone in the north; the Variscan-Hercynian suture to the south; the Tornquist Zone to the southwest; and the Ural Mountains to the east. At c. 555 Ma during the Timanian Orogeny the northern margin became an active margin and Baltica expanded northward with

1104-477: 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 S in sulfates and C in carbonates , which were strongly influenced by an increase in atmospheric oxygen. Granites and detrital zircons have notably similar and episodic appearances in

1173-439: Is the opening and closing of an individual oceanic basin . The Wilson cycle rarely synchronizes with the timing of a supercontinent cycle. However, supercontinent cycles and Wilson cycles were both involved in the creation of Pangaea and Rodinia. Secular trends such as carbonatites , granulites , eclogites , and greenstone belt deformation events are all possible indicators of Precambrian supercontinent cyclicity, although

1242-461: 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. When any supercontinent breaks up, there will be an increase in precipitation runoff over the surface of the continental landmasses, increasing silicate weathering and

1311-500: 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. 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

1380-468: 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. 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

1449-552: Is unlikely the craton also reached into Laurentia. The margin stretches north to Novaya Zemlya where early Palaeozoic Baltica faunas have been found, but the sparsity of data makes it difficult to locate the margin in the Arctic. Ordovician faunas indicate that most of Svalbard , including Bjørnøya , was part of Laurentia, but Franz Josef Land and Kvitøya (an eastern island of the Svalbard archipelago) most likely became part of Baltica in

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1518-647: The Iapetus Ocean between the two landmasses. Laurentia quickly moved northward into low latitudes but Baltica remained an isolated continent in the temperate mid-latitudes of the Southern Hemisphere, closer to Gondwana , on which endemic trilobites evolved in the Early and Middle Ordovician. During the Ordovician, Baltica moved northward, approaching Laurentia, which again allowed trilobites and brachiopods to cross

1587-523: The Mesoproterozoic , primarily by lateral accretion of juvenile arcs, and in ~1000 Ma Nuna collided with other land masses, forming Rodinia . Between ~825 and 750 Ma Rodinia broke apart. 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 . The second model (Kenorland-Arctica)

1656-403: The upper mantle by replenishing the large-ion lithophile elements , volcanism affects plate movement. 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

1725-569: The Atlantic ocean like puzzle pieces. For the period before Pangaea, there are two contrasting models for supercontinent evolution through geological time . 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

1794-588: The Caledonian orogeny until the formation of the Ural Mountains. These terranes can be linked to either northeastern Laurentia, Baltica, or Siberia because of a similar sequence of fossils; detrital zircon from 2–1 Ga-old sources and evidence of Grenvillian magmatism; and magmatism and island arcs from the Late Neoproterozoic and Ordovician-Silurian. From at least 1.8 Ga to at least 0.8 Ga

1863-652: The Iapetus Ocean. In the Silurian, c. 425 Ma, the final collision between Scotland-Greenland and Norway resulted in the closure of the Iapetus and the Scandian Orogeny . Baltica is a very old continent and its core is a very well-preserved and thick craton. Its current margins, however, are the sutures that are the result of mergers with other, much younger continental blocks. These often deformed sutures do not represent

1932-624: The Mesoproterozoic and Neoproterozoic. 750–600 million years ago, Baltica and Laurentia rotated clockwise together and drifted away from the Equator towards the South Pole where they were affected by the Cryogenian Varanger glaciations . Initial rifting between the two continents is marked by the c. 650 Ma Egersund dike swarm in southern Norway and from 600 Ma they began to rotate up to 180° relative to each other, thus opening

2001-757: The Neoproterozoic. The Western Gneiss Region in western Norway is composed of 1650–950 Ma-old gneisses overlain by continental and oceanic allochthons that were transferred from Laurentia to Baltica during the Scandian orogeny. The allochthons were accreted to Baltica during the closure of the Iapetus Ocean c. 430–410 Ma; Baltica's basement and the allochthons were then subducted to UHP depth c. 425–400 Ma; and they were finally exhumed to their present location c. 400–385 Ma. The presence of micro-diamonds in two islands in western Norway, Otrøya and Flemsøya , indicate that this margin of Baltica

2070-726: The Novaya Zemlya archipelago. The margin follows the bent shape of Novaya Zemlya which was caused in the Late Permian by the Siberian Traps . It is clear from Baltic endemic fossils in Novaya Zemlya that the islands have been part of Baltica since the Early Palaeozoic, whereas the Taymyr Peninsula farther east was part of the passive margin of Siberia in the Early Palaeozoic. Northern Taymyr, together with Severnaya Zemlya and parts of

2139-527: The Peronopsidae are diminutive, with the headshield (or cephalon ) and tailshield (or pygidium ) of approximately the same size (or isopygous ) and outline. Like all Agnostina, Peronopsidae have only two thorax segments. The cephalon and pygidium usually have a complete set of furrows. The preglabellar furrow - between the front and the central raised area of the cephalon (or glabella ) - is lacking or incomplete. The cephalon carries no spines. The border around

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2208-402: 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

2277-478: The Silurian. Some Norwegian terranes have faunas distinct from those of either Baltica or Laurentia as a result of being island arcs that originated in the Iapetus Ocean and were later accreted to Baltica. The Baltica craton most likely underlies these terranes and the continent-ocean boundary passes several kilometres off Norway, but, since the North Atlantic opened c. 54 Ma where the Iapetus Ocean closed, it

2346-481: 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). 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. Though precipitation rates during monsoonal circulations are difficult to predict, there

2415-695: The Timanide Orogeny. The Taymyr Peninsula , in contrast, never was part of Baltica: southern Taymyr was part of Siberia whilst northern Taymyr and the Severnaya Zemlya archipelago were part of the independent Kara Terrane in the early Palaeozoic. The eastern margin, the Uralide orogen, extends 2,500 km (1,600 mi) from the Arctic Novaya Zemlya archipelago to the Aral Sea . The orogen contains

2484-574: The Urals. The basement of the eastern margin is composed of an Archaean craton, metamorphosed rocks at least 1.6 Ga old, which is surrounded by the fold belt of the Timanide orogeny and overlain by Mesoproterozoic sediments. The margin became a passive margin facing the Ural Ocean in the Cambrian–Ordovician. The eastern margin stretches south through the Ural Mountains from the northern end of

2553-399: 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

2622-626: The accretion of a series of continental blocks: the Timan-Pechora Basin , the northernmost Ural Mountains, and the Novaya Zemlya islands. This expansion coincided with the Marinoan or Varanger glaciations , also known as Snowball Earth . Terranes of the North American Cordillera , including Alaska-Chukotka , Alexander, Northern Sierra, and Eastern Klamath, share a rift history with Baltica and most likely were part of Baltica from

2691-400: 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

2760-414: The breakup of Precambrian supercontinents and the lack of land plants as a carbon sink . 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

2829-422: 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. 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

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2898-452: The collision of three Archaean - Proterozoic continental blocks: Fennoscandia (including the exposed Baltic Shield ), Sarmatia ( Ukrainian Shield and Voronezh Massif ), and Volgo-Uralia (covered by younger deposits). Sarmatia and Volgo-Uralia formed a proto- craton (sometimes called "Proto-Baltica") at c. 2.0 Ga which collided with Fennoscandia c. 1.8–1.7 Ga. The sutures between these three blocks were reactivated during

2967-723: The consumption of CO 2 . 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. Erroneous conclusions are more likely to be made when models are limited to one climatic configuration (which is usually present-day). 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,

3036-452: The contemporary Earth became dominant only during the latter part of geological times. This approach was widely criticized by many researchers as it uses incorrect application of paleomagnetic data. A supercontinent cycle is the break-up of one supercontinent and the development of another, which takes place on a global scale. Supercontinent cycles are not the same as the Wilson cycle , which

3105-537: The crust of the Arctic Ocean, formed the Kara Terrane. The Urals Mountains formed in the mid and late Palaeozoic when Laurussia collided with Kazakhstania , a series of terranes. The eastern margin, however, originally extended farther east to an active margin bordered by island arcs , but those parts have been compressed, fractured, and distorted especially in the eastern Urals. The early Palaeozoic eastern margin

3174-591: The earliest family of the Agnostina. This implicates that the earliest Peronopsid genus ( Archaeagnostus ) probably descended directly from the Eodiscoid genus Tannudiscus ( Weymouthiidae ). Some scholars do not consider the Agnostina true trilobites, and consequently rejected the idea that they were related to the Eodiscina. Many lineages are thought to have evolved within the Peronopsidae, six of which gave rise to later Agnostina families. Like all Agnostida, members of

3243-416: The early continental crust to aggregate into Protopangea. 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

3312-629: 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. Continents affect

3381-440: The environment throughout time. 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. 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

3450-661: The gaps. These detrital zircons are taken from the sands of major modern rivers and their drainage basins . Oceanic magnetic anomalies and paleomagnetic data are the primary resources used for reconstructing continent and supercontinent locations back to roughly 150 Ma. [REDACTED] Africa [REDACTED] Antarctica [REDACTED] Asia [REDACTED] Australia [REDACTED] Europe [REDACTED] North America [REDACTED] South America [REDACTED] Afro-Eurasia [REDACTED] Americas [REDACTED] Eurasia [REDACTED] Oceania Baltica Baltica

3519-474: 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

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3588-462: The large size of Pangaea. And, just like today, coastal regions experienced much less variation. 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

3657-433: 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

3726-597: The original, Precambrian–early Palaeozoic extent of Baltica; for example, the curved margin north of the Urals running parallel to Novaya Zemlya was probably deformed during the eruption of the Siberian Traps in the Late Permian and Early Triassic . Baltica's western margin is the Caledonide orogen , which stretches northward from the Scandinavian Mountains across Barents Sea to Svalbard . Its eastern margin

3795-445: The pygidium is not forked. 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; 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

3864-479: The rate of heat transport must increase to become greater than the rate of radiative cooling. Through climate models, alterations in atmospheric CO 2 content and ocean heat transport are not comparatively effective. CO 2 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

3933-527: 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

4002-571: The record of at least two collisions between Baltica and intra-oceanic island arcs before the final collision between Baltica and Kazakhstania - Siberia during the formation of Pangaea . The Silurian-Devonian island arcs were accreted to Baltica along the Main Uralian Fault , east of which are metamorphosed fragments of volcanic arc mixed with small amounts of Precambrian and Paleozoic continental rocks. However, no rocks unambiguously originating from either Kazakhstania or Siberia have been found in

4071-553: The rest. The following table names reconstructed ancient supercontinents, using Bradley's 2011 looser definition, with an approximate timescale of millions of years ago (Ma). 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

4140-471: 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

4209-591: 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 Fe 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 Fe had to be transported during continental erosion. A rise in atmospheric oxygen prevents Fe transport, so

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4278-463: The southwestern margin of Baltica was connected to Amazonia while the southeast margin was connected to the West African Craton . Baltica, Amazonia, and West Africa rotated 75° clockwise relative to Laurentia until Baltica and Amazonia collided with Laurentia in the 1.1–0.9 Ga Grenville - Sveconorwegian - Sunsás orogenies to form the supercontinent Rodinia . When the break-up of Rodinia

4347-550: 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. Plate tectonics and the chemical composition of the atmosphere (specifically greenhouse gases ) are

4416-403: 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

4485-485: 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. 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,

4554-422: 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. Oxygen levels of the Archaean were negligible, and today they are roughly 21 percent. It

4623-438: 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. 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 ,

4692-715: Was buried c. 120 km (75 mi) for at least 25 million years around 429 Ma shortly after the Baltica-Laurentia collision. The Baltica-Laurentia-Avalonia triple junction in the North Sea is the southwest corner of Baltica. The Baltica-Laurentia suture stretching northeast from the triple junction was deformed in the Late Cambrian in the Scandinavian Caledonides as well as in the Scandian Orogeny during

4761-465: Was complete c. 0.6 Ga Baltica became an isolated continent — a 200 million year period when Baltica was truly a separate continent. Laurentia and Baltica formed a single continent until 1.265 Ga which broke up some time before 0.99 Ga. After the subsequent closure of the Mirovoi Ocean Laurentia, Baltica and Amazonia remained merged until the opening of the Iapetus Ocean in

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