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Arctica
Arctica or Arctida was an ancient continent which formed approximately 2.565 billion years ago in the Neoarchean era. It was made of Archaean cratons, including the Siberian Craton, with its Anabar/Aldan shields in Siberia, and the Slave, Wyoming, Superior, and North Atlantic cratons in North America. Arctica was named by because the Arctic Ocean formed by the separation of the North American and Siberian cratons. Russian geologists writing in English call the continent "Arctida" since it was given that name in 1987, alternatively the Hyperborean craton, in reference to the hyperboreans in Greek mythology. Nikolay Shatsky () was the first to assume that the crust in the Arctic region was of continental origin. Shatsky, however, was a "fixist" and, erroneously, explained the presence of Precambrian and Paleozoic metamorphic rocks on the New Siberian, Wrangel, and De long Islands with subduction. "Mobilists", on the other hand, also erroneously, proposed that North Amer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ur (continent)
Ur is a hypothetical supercontinent that formed in the Archean (3.1 billion). In a reconstruction by Rodgers, Ur is half a billion years older than Arctica and, in the early period of its existence, it was probably the only continent on Earth, and as such can be considered a supercontinent, though it was probably smaller than present-day Australia. In more recent works geologists often refer to both Ur and other proposed Archaean continental assemblages as supercratons. Ur can, nevertheless, be half a billion years younger than Vaalbara, but the concepts of these two early cratonic assemblages are incompatible. Incompatible reconstructions About 1,300–1,071 Mya, Ur joined the continents Nena and Atlantica to form the supercontinent Rodinia. In the reconstruction of , Ur remained the nucleus of East Gondwana until the break-up of Gondwana. In other reconstructions, however, India and East Antarctica did not collide until Rodinia formed 1,071 Mya. Furthermore, in the Early ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Siberia (continent)
Siberia, also known as Angaraland (or simply Angara) and Angarida, is an ancient craton in the heart of Siberia. Today forming the Central Siberian Plateau, it was an independent continent before the Permian period. The Verkhoyansk Sea, a passive continental margin, was fringing the Siberian Craton to the east in what is now the East Siberian Lowland. Angaraland was named in the 1880s by Austrian geologist Eduard Suess who erroneously believed that in the Paleozoic there were two large continents in the Northern Hemisphere: "Atlantis", North America connected to Europe by a peninsula (=Greenland and Iceland); and "Angara-land", eastern Asia, named after the Angara River in Siberia. Precambrian history About 2.5 billion years ago (Siderian), Siberia was part of a continent called Arctica, along with the Canadian Shield. Around 1.1 billion years ago (Stenian), Siberia became part of the supercontinent of Rodinia, a state of affairs which lasted until the Cryogenian about 750 mill ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Siberian Craton
Siberia, also known as Angaraland (or simply Angara) and Angarida, is an ancient craton in the heart of Siberia. Today forming the Central Siberian Plateau, it was an independent continent before the Permian period. The Verkhoyansk Sea, a passive continental margin, was fringing the Siberian Craton to the east in what is now the East Siberian Lowland. Angaraland was named in the 1880s by Austrian geologist Eduard Suess who erroneously believed that in the Paleozoic there were two large continents in the Northern Hemisphere: "Atlantis", North America connected to Europe by a peninsula (=Greenland and Iceland); and "Angara-land", eastern Asia, named after the Angara River in Siberia. Precambrian history About 2.5 billion years ago (Siderian), Siberia was part of a continent called Arctica, along with the Canadian Shield. Around 1.1 billion years ago (Stenian), Siberia became part of the supercontinent of Rodinia, a state of affairs which lasted until the Cryogenian about 750 million ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nena (supercontinent)
Nena, an acronym for Northern Europe–North America, was the Early Proterozoic amalgamation of Baltica and Laurentia into a single "cratonic landmass", a name first proposed in 1990. Since then several similar Proterozoic supercontinents have been proposed, including Nuna and Arctica, that include other Archaean cratons, such as Siberia and East Antarctica. In the original concept Nena formed in the Penokean, Makkovikan, Ketilidian, and Svecofennian orogenies. However, because Nena excludes several known Archaean cratons, including those in India and Australia, it is strictly speaking not a supercontinent. Although Nena and Nuna share many similarities, Nena accounted for a larger landmass than Nuna. This extended landmass included the Angara, Antarctica, Baltica, Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aldan Shield
Aldan Shield (russian: Алданский щит) is a shield in Siberia. It is an exposed basement of the Siberian Craton. Together with the Anabar Shield further to the northwest, the Aldan Shield is one of the main features of the craton. The Aldan Shield geological region coincides geographically with parts of the Aldan Highlands and Olyokma-Chara Plateau, located at the southern end of the Sakha Republic and the eastern end of Irkutsk Oblast.Google Earth The exposed crust parts of the shield date back to the Archean and reflect the first phases of accretion of the crust. They only emerge in a few areas, the eastern and northern sectors of the shield being largely covered by sediments accumulated between the end of the Precambrian and the Cambrian, while in the western and southern regions they have undergone processes of tectonic rejuvenation that have brought about the formation of new structures above and below. On the Aldan Shield there is the only charoite deposit know ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canadian Shield
The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), the ancient geologic core of the North American continent. Glaciation has left the area with only a thin layer of soil, through which exposures of igneous bedrock resulting from its long volcanic history are frequently visible. As a deep, common, joined bedrock region in eastern and central Canada, the Shield stretches north from the Great Lakes to the Arctic Ocean, covering over half of Canada and most of Greenland; it also extends south into the northern reaches of the United States. Geographical extent The Canadian Shield is a physiographic division comprising four smaller physiographic provinces: the Laurentian Upland, Kazan Region, Davis and James. The shield extends into the United States as the Adirondack Mountains (connected by the Fro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anabar Shield
Anabar Shield (russian: Анабарский щит) is a shield in Siberia. It is an exposed basement of the Siberian Craton. Together with the Aldan Shield to the southeast, the Anabar Shield is one of the main features of the craton. On the surface it appears as an upland of moderate height, built of gneisses and crystalline shales folded in the Archean. There are numerous dislocations and intrusions. The outer zone has slightly undulated layers of Proterozoic deposits.Анабарский массив The Anabar Shield coincides geographically with the |
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. Description The most recent supercontinent, Pangaea, formed about 300 million years ago (0.3 Ga). There are two different views on the history of earlier supercontinents. The first proposes a series of supercontinents: Vaalbara ( 3.6 to c. 2.8 billion years ago); Ur ( 3 billion years ago); Kenorland ( 2.7 to 2.1 billion years ago); Columbia ( 1.8 to 1.5 billion years ago); Rodinia ( 1.25 billion to 750 million years ago); and Pannotia ( 600 million years a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gigaannum
A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the planet, four seasons are generally recognized: spring, summer, autumn and winter. In tropical and subtropical regions, several geographical sectors do not present defined seasons; but in the seasonal tropics, the annual wet and dry seasons are recognized and tracked. A calendar year is an approximation of the number of days of the Earth's orbital period, as counted in a given calendar. The Gregorian calendar, or modern calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars. For the Gregorian calendar, the average length of the calendar year (the mean y ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleocontinent
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 expo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages of break-up, involving the separation of Antarctica from South America (forming the Drake Passage) and Australia, occurred during the Paleogene. 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 (see ), it is also commonly called Gondwanaland. Gondwana was formed by the accretion of several cratons. Eventually, Gondwana became the largest piece of continental crust of the Palaeozoic Era, covering an area of about , about one-fifth of the Earth's surface. During the Carboniferous Period, it merged with Laurasia to form a larger supercontinent called Pangaea. Gondwana (and Pan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subduction
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Subduction is possible because the cold oceanic lithosphere is slightly denser than the underlying asthenosphere, the hot, ductile layer in the upper mantle underlying the cold, rigid lithosphere. Once initiated, stable subduction is driven mostly by the negative buoyancy of the de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
