Pangean megamonsoon

Last updated

The Pangean megamonsoon refers to the theory that the supercontinent Pangea experienced a distinct seasonal reversal of winds, which resulted in extreme transitions between dry and wet periods throughout the year. Pangea was a conglomeration of all the global continental land masses, which lasted from the late Carboniferous to the mid-Jurassic. [1] The megamonsoon intensified as the continents continued to shift toward one another and reached its maximum strength in the Triassic, when the continental surface area of Pangea was at its peak. [2] [3]

Contents

The megamonsoon would have led to immensely arid regions along the interior regions of the continent. Those areas would have been nearly uninhabitable, with extremely hot days and frigid nights. The coasts experienced seasonality, however, and transitioned from rainy weather in the summer to dry conditions during the winter. [3]

Monsoon circulation

Monsoon circulations, defined as a seasonal reversal of winds, exhibit large shifts in precipitation patterns across the impacted region. Monsoons are therefore characterized by two primary seasons: rainy and dry. They are induced by the presence of at least one large land mass and large body of water in close proximity to each other. The most commonly studied present-day monsoon circulation is the East Asian Monsoon.

Discovery

The concept of a Pangean monsoon circulation was first proposed in 1973. [3] The evaporites in the geologic record suggest vast and extensive regions of persistent dry conditions near the Pangean centre, serving as the initial evidence for the theory’s dissemination. The interior of the supercontinent, especially the eastern portion, would have been extremely dry as the hemispheric pressure systems driving the circulation would have diverted nearly all atmospheric moisture away from the region. [3] The later indication of a monsoon-driven climate was acquired via the examination of coal deposits along the exterior portions of the continent. The presence of both features in the geologic record suggest monsoonal circulations. [3]

As the theory of the Pangean megamonsoon began to increase in credibility, paleoclimatologists predicted the climatological impacts of the circulation to ascertain whether observations and models supported the hypothesis. The general consensus listed four primary signs that needed to be present to validate the existence of megamonsoon. [3]

  1. The lithologic indicators of seasonality should span broad distances along the Pangean coasts.
  2. Evidence depicting a deviation from zonal flow regimes needed to be identified.
  3. Records should indicate that the equatorial regions of Pangea would have been plagued by persistent aridity.
  4. Models and geologic observations would need to demonstrate that this circulation peaked during the Triassic. [3]

Monsoon climate on Pangea

In the Northern Hemisphere's summer, when Earth’s axial tilt was directed toward the sun, Laurasia would have received the most direct solar insolation, which would have yielded a broad area of warm, rising air and low surface pressure over the continent. Models have suggested that this seasonal low was positioned at 35° latitude, relatively near the Tethys Ocean. [4] In Gondwana, high pressure would have dominated, as the land would have been receiving less solar radiation and therefore experiencing cooler temperatures. [5]

The pressure-gradient force dictates that air will travel from regions of high to low pressure. That would have driven the atmospheric flow from the Southern Hemisphere toward Laurasia during which it would cross the Tethys Ocean. Water from the Tethys would evaporate into the air mass. Eventually, the air mass would reach the coast of Laurasia and resulted in immense amounts of precipitation. [5] Models estimate the globally-averaged precipitation to equal roughly 1,000 mm per year, with coastal regions receiving upwards of 8 mm of rain each day during the rainy season. [4] As the atmospheric flow was directed away from the Gondwana high pressure system, surface winds would have diverged, producing clear and very dry conditions across the Southern Hemisphere. [4]

Several studies have indicated that the circulation was so intense during the Triassic, it would have been capable of reversing part of the predominantly-easterly global wind flow [3] [6] [7] and so westerly winds impacted the western coast. That worked to maximize surface convergence and increased seasonality along the western coasts of each continent. [3]

During the Northern Hemisphere winter, when Earth’s tilt was directed away from the Sun, the circulation reversed as the area of maximum solar insolation shifted toward the Southern Hemisphere. Air then traveled from Laurasia (region of high pressure), across the Tethys Ocean to Gondwana (region of low pressure). Moisture advection toward the Southern Hemisphere would have fueled heavy precipitation along the Gondwana coasts, while Laurasia remained very dry. [4]

Comparison to present day

There are marked similarities between factors contributing to the East Asian monsoon and those that would have influenced Pangean climate. That supports the theory that Pangean climate was dominated by the monsoon and aids in its study by providing paleoclimatologists with a present-day example to which they can compare their findings. The width of the Tethys Ocean is believed to have been roughly the same as that of the Indian Ocean. [3] It is well documented that the Indian Ocean can provide onshore-moving air masses with enough moisture to support a monsoon-driven environment. Thus, the Tethys should have been able to as well.

Many paleoclimate models have attempted to recreate climate patterns on Pangea. The models have yielded results that are comparable with the East Asian Monsoon. For instance, one model reported that the seasonal pressure differential (wintertime high pressure – summertime low pressure) over the continent was 25 millibars, [4] while the Asian pressure varies by 36 millibars on average throughout the year. [3]

The Central Pangean Mountains potentially played a similar role in the megamonsoon as the Tibetan Plateau in the East Asian Monsoon. [3] Model simulations suggest that without the presence of the mountain range, the monsoon circulation would have been substantially weakened. [4] Higher elevations may have intensified the atmospheric circulation by maximizing the surface heating and subsequently the latent heat release during the summer rainy season. [8] There is still significant uncertainty regarding the extent of the impact that range would have had, however, because mountain elevations are unknown.

Geologic record

Coal and evaporites

Coal is typically an indicator of moist climates since it needs both plant matter and humid conditions to form. The poleward progression of coal deposits with time suggests that the regions of maximum rainfall shifted away from the equator. Nonetheless, the employment coal as climatic indicator of precipitation is still employed with caution by geologists, as its creation secondarily depends on rainfall amounts. [3] When a significant amount of evaporation occurs, evaporites are formed, which therefore signifies arid conditions.

Loess

Loess, or windblown dust, can be used as an indicator of past atmospheric circulation patterns. Without the presence of the monsoon, surface winds across the globe would have been primarily zonal and easterly. The geologic record, however, indicates that winds exhibited a meridional cross-equatorial pattern but also that western Pangea experienced westerly flow during the peak period of the megamonsoon. [3] [9] [10]

Paleontological evidence

Fossils dating back to Pangean times also support the claim that a strongly-monsoonal circulation dominated the supercontinent’s climate. For example, tree rings (also called growth rings) provide convincing proof of distinct changes in annual weather patterns. Trees rooted in areas that do not experience seasonality will not exhibit rings within their trunks as they grow. Fossilized wood excavated from what was once coastal, mid-latitude Pangea, however, display the clear presence of rings. [2] Other paleoflora suggest that a significant portion of the year would have been dominated by a warm, moist season. Large, smooth leaf shapes with thin cuticles and symmetric distribution of stomata, as well as tropical fern species have been uncovered from those regions. [2]

The invertebrates and vertebrates that existed on Pangea offer further evidence of seasonality. For instance, unionid bivalve shells exhibit uniform banding patterns. Unionid bivalves were aquatic organisms that required shallow, oxygen-rich lakes to thrive. During the summer, when rain was persistent, their respiration occurred aerobically and precipitated calcium carbonate to grow their shells. In the winter, when precipitation ceased, the shallow aquatic environments within the Pangean continent began to dry up. Thus, unionid bivalves depleted their environments of oxygen and eventually had to resort to anaerobic processes for respiration. The anaerobic respiration yielded acidic waste, which reacted with the calcium carbonate shell, creating a darker ring and marking the presence of a distinct dry season. Once the summer rains returned, aerobic respiration was restored and calcium carbonate was once again produced. The transition from dry winters to rainy summers is therefore recorded in these alternating patterns of light and dark bands on the unionid bivalve shells. [2]

Lungfish burrowing patterns also correlate well with the rise and the fall of the water levels. [2] The height of the water would have increased during the rainy season, but then decreased rapidly as the winds shifted and diverted moisture away from the location, thus initiating the dry season. Additional evidence of seasonality can be observed in the fossilized carcasses of other vertebrate organisms. These show signs of substantial drying, which would have occurred during the winter, before they were buried and preserved by mudflow (resulting from a persistent rainy period). [2]

Evolution

Carboniferous

During much of the Carboniferous, the tropics would have experienced humid conditions, and the high latitudes of Gondwana were covered by glaciers. [11] Still, the first signs of the poleward movement of moisture arose during the late Carboniferous. Geologists have tracked regions of past coal accumulation as they began to be deposited further from the equator with time, evidence of a shift in precipitation patterns from the tropics toward the higher latitudes. [3] Still, land mass distribution remained more heavily concentrated in the Southern Hemisphere. Atmospheric flow, therefore, remained largely zonal, [12] indicating that the monsoon circulation had not yet begun to dominate the climatic pattern.

Permian

By Permian times, the monsoon circulation is apparent in the lithology. Winds with a westerly component (indicative of the summer monsoon, or wet season) are observed for the Early Permian. [13] The continents continued to drift northward. As they did so, the land mass became more evenly distributed across the equator and the megamonsoon continued to intensify.

Gondwana’s progression northward also influenced its gradual deglaciation. [14] Climate models indicate that low pressure systems strengthened as planetary ice cover decreased, thus exaggerating the effect of the monsoon. This also acted to magnify the aridity of the tropics. It is therefore suggested that glacial-interglacial patterns had a significant effect on the Pangean monsoonal circulation. [15] Models have also indicated that worldwide carbon dioxide substantially increased between Carboniferous and Permian times and resulted in increased temperatures.

Triassic

During the Triassic, the megamonsoon reached its maximum intensity, which is believed to be a result of the supercontinent attaining its largest surface area during this period from the final addition of Siberia and the North and South China cratons. Land mass was also equally distributed between the Northern and Southern Hemispheres, was nearly perfectly bisected by the equator, and extended from 85°N to 90°S. [3]

Both the increase in Pangean surface area and the equitable dissemination of the land mass across the hemispheres maximized surface heating during the summer. [3] The stronger the surface heating was, the more extreme the convection. By intensifying rising motion, the central pressure of the summertime surface low would have dropped. That, in turn, increased the hemispheric pressure gradient and amplified the cross-equatorial flow.

Additionally, the planet was experiencing a greenhouse climate during the Triassic, which resulted in continents completely devoid of ice, including the polar regions. [16] Interglacial periods correlate well with an intensification of the monsoon circulation. [17] Records clearly indicate a western component to the wind direction throughout this time period. It is also from that period that the paleontological evidence is most prevalent. [18] [3]

Jurassic

During the early Jurassic, the supercontinent continued to shift northward. The coasts along the Tethys Ocean grew more persistently humid. [19] The monsoon circulation began to weaken through Jurassic time, when the continents started to drift apart. [3] Records indicate that large-scale atmospheric flow progressively returned to a primarily zonal pattern. [5] Climatic patterns therefore became less extreme across the continents.

Model simulations

Today, the presence of the Pangean megamonsoon is generally accepted by the paleoclimate community. There is a substantial amount of evidence, both in the geologic record and model simulations, to support its existence. [4] [2] [3] [20] [21] Nevertheless, a significant amount of uncertainty still remains, particularly from a modeling perspective. One of the greater unknowns paleoclimatologists face is the impact of the Central Pangean Mountains. Model simulations have suggested that without the presence of the mountain range, the monsoon circulation would have been substantially weakened. [4]

Mountains were located to the north of the Tethys Ocean and resulted from the northward progression and subsequent subduction of the paleo-Tethyan plate. [2] However, the height of these mountains has yet to be quantified. Scientists have acknowledged that approximating their elevation is of “capital importance”. [22] Extremely high mountain ranges (rivaling the Himalayas) would have magnified atmospheric circulation, intensified the low pressure system, accelerated moisture transport to the coasts, and induced a rain shadow effect, promoting aridity on the leeward side of the range. [23]

Studies also continue to examine the impact of orbital cycles on the monsoon circulation. [24] [4] [25] The monsoon during the late Triassic appears to have been particularly impacted by Milankovich cycles for a period extending over at least 22 million years. Orbital eccentricity seems to have significantly affected precipitation cycles, but further research is required to better understand this correlation. [26]

Climate modelers are trying to further understand and account for the surface and deep water circulations of the Panthalassic Ocean. The transport of heat resulting from these circulations significantly alters the simulated monsoon; therefore accurately representing them is of great importance. [4] [27] Continued research will eventually provide scientists with a much more complete comprehension of the progression and behavior of the megamonsoon that dominated the Pangean climate.

Notes

  1. ↑ Smith, pp.187, 135-179.
  2. 1 2 3 4 5 6 7 8 Dubiel, Russell F; Parrish, Judith Totman; Parrish, J. Michael; Good, Steven (August 1991). "The Pangaean Megamonsoon—Evidence from the Upper Triassic Chinle Formation, Colorado Plateau". PALAIOS. 6 (4): 347–370. Bibcode:1991Palai...6..347D. doi:10.2307/3514963. JSTOR   3514963. S2CID   54856289.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Parrish, Judith Totman (March 1993). "Climate of the Supercontinent Pangea". Journal of Geology. 101 (2): 215–233. Bibcode:1993JG....101..215P. doi:10.1086/648217. S2CID   128757269.
  4. 1 2 3 4 5 6 7 8 9 10 Kutzbach, Judith Totman; Gallimore, R.G. (20 March 1989). "Pangaean climates: Megamonsoons of the megacontinent". Journal of Geophysical Research. 94 (D3): 3341–3357. doi:10.1029/JD094iD03p03341.
  5. 1 2 3 Parrish, Judith Totman; Peterson, Fred (April 1988). "Wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western United States—A comparison". Sedimentary Geology. 56 (1–4): 261–282. doi:10.1016/0037-0738(88)90056-5.
  6. ↑ Soreghan, M.S., Soreghan, G.S., and Hamilton, M.A., 2002: Paleowinds inferred from detrital-zircon geochronology of upper Paleozoic loessite, western equatorial Pangea. Geology, 30, 695-698.
  7. ↑ Tabor, N.J. and I.P. Montañez, 2002: Shifts in late Paleozoic atmospheric circulation over western equatorial Pangaea: Insights from pedogenic mineral ɗ18O compositions. Geology, 30, 12, 1127-1130.
  8. ↑ Dubiel et al. 1991
  9. ↑ Soreghan, M.S., Soreghan, G.S., and Hamilton, M.A., 2002: Paleowinds inferred from detrital-zircon geochronology of upper Paleozoic loessite, western equatorial Pangea. Geology, 30, 695-698.
  10. ↑ Tabor, N.J. and I.P. Montañez, 2002: Shifts in late Paleozoic atmospheric circulation over western equatorial Pangaea: Insights from pedogenic mineral ɗ18O compositions. Geology, 30, 12, 1127-1130.
  11. ↑ Francis, J.E., 2009: Palaeoclimates of Pangea- geological evidence. Canadian Society of Petroleum Geologists, 17, 265-274.
  12. ↑ Francis, J.E., 2009: Palaeoclimates of Pangea- geological evidence. Canadian Society of Petroleum Geologists, 17, 265-274.
  13. ↑ Soreghan, M.S., Soreghan, G.S., and Hamilton, M.A., 2002: Paleowinds inferred from detrital-zircon geochronology of upper Paleozoic loessite, western equatorial Pangea. Geology, 30, 695-698.
  14. ↑ Francis, J.E., 2009: Palaeoclimates of Pangea- geological evidence. Canadian Society of Petroleum Geologists, 17, 265-274.
  15. ↑ Miller, K.B., T.J. McCahon, R.R. West, 1996: Lower Permian (Wolfcampiam) paleosols-bearing cycles of the U.S. Midcontinent: evidence of climatic cyclicity. Journal of Sedimentary Research, 66, 71-84.
  16. ↑ Olsen, P.E. and D.V. Kent, 1995: Milankovich climate forcing in the tropics of Pangea during the late Triassic. Palaeogeography, Palaeoclimatology, Palaeoecology, 122, 1-26.
  17. ↑ Francis, J.E., 2009: Palaeoclimates of Pangea- geological evidence. Canadian Society of Petroleum Geologists, 17, 265-274.
  18. ↑ Dubiel, R.F., J.T. Parrish, J.M. Parrish, S.C. Good, 1991: The Pangaean Megamonsoon—Evidence from the Upper Triassic Chinle Formation, Colorado Plateau. Society for Sedimentary Geology, 6, 347-370.
  19. ↑ Francis, J.E., 2009: Palaeoclimates of Pangea- geological evidence. Canadian Society of Petroleum Geologists, 17, 265-274.
  20. ↑ Soreghan, M.S., Soreghan, G.S., and Hamilton, M.A., 2002: Paleowinds inferred from detrital-zircon geochronology of upper Paleozoic loessite, western equatorial Pangea. Geology, 30, 695-698.
  21. ↑ Francis, J.E., 2009: Palaeoclimates of Pangea- geological evidence. Canadian Society of Petroleum Geologists, 17, 265-274.
  22. ↑ Fluteau, F., B.J. Broutin, and G. Ramstein, 2001: The late Permian climate. What can be inferred from climate modeling concerning Pangea scenarios and Hercynian range altitude? Palaeogeography, Palaeoclimatology, Palaeoecology, 167, 39-71.
  23. ↑ Fluteau, F., B.J. Broutin, and G. Ramstein, 2001: The late Permian climate. What can be inferred from climate modeling concerning Pangea scenarios and Hercynian range altitude? Palaeogeography, Palaeoclimatology, Palaeoecology, 167, 39-71.
  24. ↑ Olsen, P.E., 1986: A 40-million-yearlake record of early Mesozoic climate forcing. Science, 234, 842-848.
  25. ↑ Olsen, P.E. and D.V. Kent, 1995: Milankovich climate forcing in the tropics of Pangea during the late Triassic. Palaeogeography, Palaeoclimatology, Palaeoecology, 122, 1-26.
  26. ↑ Olsen, P.E. and D.V. Kent, 1995: Milankovich climate forcing in the tropics of Pangea during the late Triassic. Palaeogeography, Palaeoclimatology, Palaeoecology, 122, 1-26.
  27. ↑ Peyser, C.E and D.J. Poulsen, 2008: Controls on Permo-Carboniferous precipitation over tropical Pangaea: A GCM sensitivity study. Paleogeography, Paleaoclimatology, Paleoecology, 268, 181-192.

Related Research Articles

<span class="mw-page-title-main">Carboniferous</span> Fifth period of the Paleozoic Era, 359–299 million years ago

The Carboniferous is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period 358.9 Ma to the beginning of the Permian Period, 298.9 Ma. In North America, the Carboniferous is often treated as two separate geological periods, the earlier Mississippian and the later Pennsylvanian.

The Mesozoic Era is the second-to-last era of Earth's geological history, lasting from about 252 to 66 million years ago, comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of gymnosperms and of archosaurian reptiles, such as the dinosaurs; a hot greenhouse climate; and the tectonic break-up of Pangaea. The Mesozoic is the middle of the three eras since complex life evolved: the Paleozoic, the Mesozoic, and the Cenozoic.

<span class="mw-page-title-main">Permian</span> Sixth and last period of the Paleozoic Era 299–252 million years ago

The Permian is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia.

The PaleozoicEra is the first of three geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic and ends 251.9 Ma at the start of the Mesozoic Era. The Paleozoic is subdivided into six geologic periods :

The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record. The time before the Phanerozoic, collectively called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.

<span class="mw-page-title-main">Supercontinent</span> Landmass comprising more than one continental core, or craton

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

<span class="mw-page-title-main">Triassic</span> First period of the Mesozoic Era 252–201 million years ago

The Triassic is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. The Triassic Period is subdivided into three epochs: Early Triassic, Middle Triassic and Late Triassic.

<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">Panthalassa</span> Prehistoric superocean that surrounded Pangaea

Panthalassa, also known as the Panthalassic Ocean or Panthalassan Ocean, was the vast superocean that encompassed planet Earth and surrounded the supercontinent Pangaea, the latest in a series of supercontinents in the history of Earth. During the Paleozoic–Mesozoic transition, the ocean occupied almost 70% of Earth's surface, with the supercontinent Pangaea taking up less than half. The original, ancient ocean floor has now completely disappeared because of the continuous subduction along the continental margins on its circumference. Panthalassa is also referred to as the Paleo-Pacific or Proto-Pacific because the Pacific Ocean is a direct continuation of Panthalassa.

<span class="mw-page-title-main">Intertropical Convergence Zone</span> Meteorological phenomenon

The Intertropical Convergence Zone, known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. It encircles Earth near the thermal equator though its specific position varies seasonally. When it lies near the geographic Equator, it is called the near-equatorial trough. Where the ITCZ is drawn into and merges with a monsoonal circulation, it is sometimes referred to as a monsoon trough.

The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between 237 Ma and 201.4 Ma. It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. The corresponding series of rock beds is known as the Upper Triassic. The Late Triassic is divided into the Carnian, Norian and Rhaetian ages.

<span class="mw-page-title-main">Late Paleozoic icehouse</span> Ice age

The late Paleozoic icehouse, also known as the Late Paleozoic Ice Age (LPIA) and formerly known as the Karoo ice age, was an ice age that began in the Late Devonian and ended in the Late Permian, occurring from 360 to 255 million years ago (Mya), and large land-based ice-sheets were then present on Earth's surface. It was the second major icehouse period of the Phanerozoic. It is named after the tillite found in the Karoo Basin of western South Africa, where evidence for the ice age was first clearly identified in the 19th century.

<span class="mw-page-title-main">Hadley cell</span> Tropical atmospheric circulation feature

The Hadley cell, also known as the Hadley circulation, is a global-scale tropical atmospheric circulation that features air rising near the equator, flowing poleward near the tropopause at a height of 12–15 km (7.5–9.3 mi) above the Earth's surface, cooling and descending in the subtropics at around 25 degrees latitude, and then returning equatorward near the surface. It is a thermally direct circulation within the troposphere that emerges due to differences in insolation and heating between the tropics and the subtropics. On a yearly average, the circulation is characterized by a circulation cell on each side of the equator. The Southern Hemisphere Hadley cell is slightly stronger on average than its northern counterpart, extending slightly beyond the equator into the Northern Hemisphere. During the summer and winter months, the Hadley circulation is dominated by a single, cross-equatorial cell with air rising in the summer hemisphere and sinking in the winter hemisphere. Analogous circulations may occur in extraterrestrial atmospheres, such as on Venus and Mars.

<span class="mw-page-title-main">Cimmeria (continent)</span> Ancient string of microcontinents that rifted from Gondwana

Cimmeria was an ancient continent, or, rather, a string of microcontinents or terranes, that rifted from Gondwana in the Southern Hemisphere and was accreted to Eurasia in the Northern Hemisphere. It consisted of parts of present-day Turkey, Iran, Afghanistan, Pakistan, Tibet, China, Myanmar, Thailand, and Malaysia. Cimmeria rifted from the Gondwanan shores of the Paleo-Tethys Ocean during the Early Permian and as the Neo-Tethys Ocean opened behind it, during the Permian, the Paleo-Tethys closed in front of it. Because the different chunks of Cimmeria drifted northward at different rates, a Meso-Tethys Ocean formed between the different fragments during the Cisuralian. Cimmeria rifted off Gondwana from east to west, from Australia to the eastern Mediterranean. It stretched across several latitudes and spanned a wide range of climatic zones.

<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">Gondwana</span> Neoproterozoic to Cretaceous landmass

Gondwana was a large landmass, sometimes referred to as a supercontinent. It was formed by the accretion of several cratons, beginning c. 800 to 650Ma with the East African Orogeny, the collision of India and Madagascar with East Africa, and culminating in c. 600 to 530 Ma with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa, and the addition of Australia and Antarctica, respectively. Eventually, Gondwana became the largest piece of continental crust of the Palaeozoic Era, covering an area of some 100,000,000 km2 (39,000,000 sq mi), about one-fifth of the Earth's surface. It fused with Euramerica during the Carboniferous to form Pangea. It began to separate from northern Pangea (Laurasia) during the Triassic, and started to fragment during the Early Jurassic. The final stages of break-up, involving the separation of Antarctica from South America and Australia, occurred during the Paleogene (from around 66 to 23 million years ago. Gondwana was not considered a supercontinent by the earliest definition, since the landmasses of Baltica, Laurentia, and Siberia were separated from it. To differentiate it from the Indian region of the same name, it is also commonly called Gondwanaland.

<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.

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">Central Pangean Mountains</span> Major feature of the supercontinent

The Central Pangean Mountains were an extensive northeast–southwest trending mountain range in the central portion of the supercontinent Pangaea during the Carboniferous, Permian and Triassic periods. They were formed as a result of collision between the large landmasses of Euramerica and Gondwana during the formation of Pangaea. At its greatest elevation during the early part of the Permian period, it was comparable to the present Himalayas. Remnants of this massive mountain range include the Appalachian Mountains and Ouachita Mountains of North America as well as the Bohemian Massif and Massif Central in Europe.

<span class="mw-page-title-main">Monsoon of South Asia</span> Monsoon in Indian subcontinent

The Monsoon of South Asia is among several geographically distributed global monsoons. It affects the Indian subcontinent, where it is one of the oldest and most anticipated weather phenomena and an economically important pattern every year from June through September, but it is only partly understood and notoriously difficult to predict. Several theories have been proposed to explain the origin, process, strength, variability, distribution, and general vagaries of the monsoon, but understanding and predictability are still evolving.

References

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.