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Paleo-Tethys Ocean
The Paleo-Tethys or Palaeo-Tethys Ocean was an ocean located along the northern margin of the paleocontinent Gondwana that started to open during the Middle Cambrian, grew throughout the Paleozoic, and finally closed during the Late Triassic; existing for about 400 million years. Paleo-Tethys was a precursor to the Tethys Ocean (also called the Neo-Tethys), which was located between Gondwana and the Hunic terranes (continental fragments that broke off Gondwana and moved north). It opened as the Proto-Tethys Ocean subducted under these terranes and closed as the Cimmerian terranes (that also broke-off Gondwana and moved north) gave way to the Tethys Ocean. Confusingly, the Neo-Tethys is sometimes defined as the ocean south of a hypothesized mid-ocean ridge separating Greater India from Asia, in which case the ocean between Cimmeria and this hypothesized ridge is called the Meso-Tethys, i.e., the "Middle-Tethys". The so-called Hunic terranes are divided into the ''European H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Supercontinent Cycle
The supercontinent cycle is the quasi-periodic aggregation and dispersal of Earth's continental crust. There are varying opinions as to whether the amount of continental crust is increasing, decreasing, or staying about the same, but it is agreed that the Earth's crust is constantly being reconfigured. One complete supercontinent cycle is said to take 300 to 500 million years. Continental collision makes fewer and larger continents while rifting makes more and smaller continents. Theory The most recent supercontinent, Pangaea, formed about 300 million years ago (0.3 Ga), during the Paleozoic era. There are two different views on the history of earlier supercontinents. Series The first theory proposes a series of supercontinents: starting with Vaalbara (3.6 to 2.8 Ga); Ur (c. 3 Ga); Kenorland (2.7 to 2.1 Ga); Columbia (1.8 to 1.5 Ga); Rodinia (1.25 Ga to 750 Ma); and Pannotia ( 600 Ma), whose dispersal produced the continents ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago (Megaannum, Ma), to the beginning of the succeeding Carboniferous period at Ma. It is the fourth period of both the Paleozoic and the Phanerozoic. It is named after Devon, South West England, where rocks from this period were first studied. The first significant evolutionary radiation of history of life#Colonization of land, life on land occurred during the Devonian, as free-spore, sporing land plants (pteridophytes) began to spread across dry land, forming extensive coal forests which covered the continents. By the middle of the Devonian, several groups of vascular plants had evolved leaf, leaves and true roots, and by the end of the period the first seed-bearing plants (Pteridospermatophyta, pteridospermatophyt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhenohercynian Basin
The Rhenohercynian Zone or Rheno-Hercynian zone in structural geology describes a Fold and thrust belt, fold belt of west and central Europe, formed during the Hercynian orogeny (about ). The zone consists of fold (geology), folded and thrust fault, thrust Devonian and early Carboniferous sedimentary rocks that were deposited in a back-arc basin along the southern margin of the then existing paleocontinent Laurussia. The Rhenohercynian Zone, named for the Rhine River and the Hercynian Forest of Antiquity, forms a narrow zone through western and central Europe, from Cornwall and Ireland in the west to the Harz mountains of central Germany in the east, including the Rhenish Massif (Ardennes, Taunus, Eifel and Hunsrück). The total length of this ancient basin (the Rhenohercynian Basin) could have been more than 2500 km. In the east the basin merges with the East-Silesian basin of southern Poland. The sedimentary rocks that were laid down in the basin are often weakly metamorphis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben with normal faulting and rift-flank uplifts mainly on one side. Where rifts remain above sea level they form a rift valley, which may be filled by water forming a rift lake. The axis of the rift area may contain volcanic rocks, and active volcanism is a part of many, but not all, active rift systems. Major rifts occur along the central axis of most mid-ocean ridges, where new oceanic crust and lithosphere is created along a divergent boundary between two tectonic plates. ''Failed rifts'' are the result of continental rifting that failed to continue to the point of break-up. Typically the transition from rifting to spreading develops at a triple junction where three converging rifts meet over a hotspot. Two of these evolve to t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rheic Ocean
The Rheic Ocean (; ) was an ocean which separated two major paleocontinents, Gondwana and Laurussia ( Laurentia- Baltica- Avalonia). One of the principal oceans of the Paleozoic, its sutures today stretch from Mexico to Turkey and its closure resulted in the assembly of the supercontinent Pangaea and the formation of the Variscan– Alleghenian– Ouachita orogenies. Etymology The ocean located between Gondwana and Laurentia in the Early Cambrian was named for Iapetus, in Greek mythology the father of Atlas (from which source the Atlantic Ocean ultimately gets its name), just as the Iapetus Ocean was the predecessor of the Atlantic Ocean. The ocean between Gondwana and Laurussia ( Laurentia– Baltica– Avalonia) that existed from the Early Ordovician to the Early Carboniferous was named the Rheic Ocean after Rhea, sister of Iapetus. Geodynamic evolution At the beginning of the Paleozoic Era, about 540 million years ago, most of the continental mass on Earth was clu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Euramerica
Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pangaea, drifting further north after the split and finally broke apart with the opening of the North Atlantic Ocean 56 Mya. The name is a portmanteau of Laurentia and Eurasia. Laurentia, Avalonia, Baltica, and a series of smaller terranes, collided in the Caledonian orogeny c. 400 Mya to form Laurussia. Laurussia then collided with Gondwana to form Pangaea. Kazakhstania and Siberia were then added to Pangaea 290–300 Mya to form Laurasia. Laurasia finally became an independent continental mass when Pangaea broke up into Gondwana and Laurasia. Terminology and origin of the concept Laurentia, the Palaeozoic core of North America and continental fragments that now make up part of Europe, collided with Baltica and Aval ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period Megaannum, Ma (million years ago) to the start of the Silurian Period Ma. The Ordovician, named after the Celtic Britons, Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same Rock (geology), rock beds in North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed Stratum, strata were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received international approval in 1960 (forty years after Lapworth's death), when it was adopted as an official per ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Back-arc Basin
A back-arc basin is a type of geologic Structural basin, basin, found at some convergent boundary, convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of them result from Tension (physics), tensional forces, caused by a process known as Oceanic trench#Trench rollback, oceanic trench rollback, where a subduction zone moves towards the subducting plate. Back-arc basins were initially an unexpected phenomenon in plate tectonics, as convergent boundaries were expected to universally be zones of compression. However, in 1970, Dan Karig published a model of back-arc basins consistent with plate tectonics. Structural characteristics Back-arc basins are typically very long and relatively narrow, often thousands of kilometers long while only being a few hundred kilometers wide at most. For back-arc extension to form, a subduction zone is required, but not a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
249 Global
49 may refer to: * 49 (number) * "Forty Nine", a song by Karma to Burn from the album '' V'', 2011 * one of the years 49 BC, AD 49, 1949, 2049 * 49 Pales 49 Pales () is a large, dark main-belt asteroid. It was discovered by German-French astronomer Hermann Goldschmidt on 19 September 1857 from his balcony in Paris. The asteroid is named after Pales, the goddess of shepherds in Roman mytholog ..., a main-belt asteroid * Tatra 49, a three-wheeled motor vehicle {{Numberdis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
290 Global
9 (nine) is the natural number following and preceding . Evolution of the Hindu–Arabic digit Circa 300 BC, as part of the Brahmi numerals, various Indians wrote a digit 9 similar in shape to the modern closing question mark without the bottom dot. The Kshatrapa, Andhra and Gupta started curving the bottom vertical line coming up with a -look-alike. How the numbers got to their Gupta form is open to considerable debate. The Nagari continued the bottom stroke to make a circle and enclose the 3-look-alike, in much the same way that the sign @ encircles a lowercase ''a''. As time went on, the enclosing circle became bigger and its line continued beyond the circle downwards, as the 3-look-alike became smaller. Soon, all that was left of the 3-look-alike was a squiggle. The Arabs simply connected that squiggle to the downward stroke at the middle and subsequent European change was purely cosmetic. While the shape of the glyph for the digit 9 has an ascender in most modern typefa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
