Laurasia

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Laurasia
Laurasia-Gondwana.svg
Map of Pangaea with Laurasia and Gondwana.
Historical continent
Formed1,071 Mya (Proto-Laurasia)
253 Mya
Type Geological supercontinent
Today part of
Smaller continents
Tectonic plate

Laurasia ( /lɔːˈrʒə, -ʃiə/ ) [1] was the more northern of two supercontinents (the other being Gondwana) that formed part of the Pangaea supercontinent around 335 to 175 million years ago (Mya). It separated from Gondwana 215 to 175 Mya (beginning in the late Triassic period) during the breakup of Pangaea, drifting farther north after the split.

Supercontinent 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, many earth scientists use a different definition: "a clustering of nearly all continents", which leaves room for interpretation and is easier to apply to Precambrian times.

Gondwana Neoproterozoic to Carboniferous supercontinent

Gondwana, , was a supercontinent that existed from the Neoproterozoic until the Jurassic.

Pangaea 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 earlier continental units approximately 335 million years ago, and it began to break apart about 175 million years ago. In contrast to the present Earth and its distribution of continental mass, much of Pangaea was in the southern hemisphere and surrounded by a superocean, Panthalassa. Pangaea was the most recent supercontinent to have existed and the first to be reconstructed by geologists.

Contents

The name combines the names of Laurentia, the name given to the North American craton, and Eurasia. As suggested by the geologic naming, Laurasia included most of the land masses which make up today's continents of the Northern Hemisphere, chiefly Laurentia, Baltica, Siberia, Kazakhstania, and the North China and East China cratons.

Laurentia A large continental craton that forms the ancient geological core of the North American continent

Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of the North American continent. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although originally it also included the cratonic areas of Greenland and also the northwestern part of Scotland, known as the Hebridean Terrane. During other times in its past, Laurentia has been part of larger continents and supercontinents and itself consists of many smaller terranes assembled on a network of Early Proterozoic orogenic belts. Small microcontinents and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable Precambrian craton seen today.

Craton Old and stable part of the continental lithosphere

A craton is an old and stable part of the continental lithosphere, where the lithosphere consists of the Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by younger sedimentary rock. They have a thick crust and deep lithospheric roots that extend as much as several hundred kilometres into the Earth's mantle.

Eurasia The combined continental landmass of Europe and Asia

Eurasia is the combined continental landmass of Europe and Asia. The term is a portmanteau of its constituent continents. Located primarily in the Northern and Eastern Hemispheres, it is bordered by the Atlantic Ocean to the west, the Pacific Ocean to the east, the Arctic Ocean to the north, and by Africa, the Mediterranean Sea, and the Indian Ocean to the south. The division between Europe and Asia as two different continents is a historical social construct, with no clear physical separation between them; thus, in some parts of the world, Eurasia is recognized as the largest of the six, five, or even four continents on Earth. In geology, Eurasia is often considered as a single rigid megablock. However, the rigidity of Eurasia is debated based on paleomagnetic data.

Origin

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Although Laurasia is known as a Mesozoic phenomenon, today it is believed that the same continents that formed the later Laurasia also existed as a coherent supercontinent after the breakup of Rodinia around 750 million years ago. To avoid confusion with the Mesozoic continent, this is referred to as Proto-Laurasia. It is believed that Laurasia did not break up again before it recombined with the southern continents to form the late Precambrian supercontinent of Pannotia, which remained until the early Cambrian. Laurasia was assembled, then broken up, due to the actions of plate tectonics, continental drift, and seafloor spreading.

The Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles and the Age of Conifers.

Rodinia Hypothetical neoproterozoic supercontinent from between about a billion to about three quarters of a billion years ago

Rodinia is a Neoproterozoic supercontinent that was assembled 1.1–0.9 billion years ago and broken up 750–633 million years ago. Valentine & Moores 1970 were probably the first to recognise a Precambrian supercontinent, which they named 'Pangaea I'. It was renamed 'Rodinia' by McMenamin & McMenamin 1990 who also were the first to produce a reconstruction and propose a temporal framework for the supercontinent.

The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.

Breakup and reformation

During the Cambrian, Laurasia was largely located in equatorial latitudes and began to break up, with North China and Siberia drifting into latitudes further north than those occupied by continents during the previous 500 million years. By the Devonian, North China was located near the Arctic Circle and it remained the northernmost land in the world during the Carboniferous Ice Age between 300 and 280 million years ago. No evidence, though, exists for any large-scale Carboniferous glaciation of the northern continents. This cold period saw the rejoining of Laurentia and Baltica with the formation of the Appalachian Mountains and vast coal deposits, found in regions including West Virginia, Britain, and Germany.

The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, England, where rocks from this period were first studied.

Arctic Circle Boundary of the Arctic

The Arctic Circle is one of the two polar circles and the most northerly of the five major circles of latitude as shown on maps of Earth. It marks the northernmost point at which the centre of the noon sun is just visible on the December solstice and the southernmost point at which the centre of the midnight sun is just visible on the June solstice. The region north of this circle is known as the Arctic, and the zone just to the south is called the Northern Temperate Zone.

The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago (Mya), to the beginning of the Permian Period, 298.9 Mya. The name Carboniferous means "coal-bearing" and derives from the Latin words carbō ("coal") and ferō, and was coined by geologists William Conybeare and William Phillips in 1822.

Siberia moved southwards and joined with Kazakhstania, a small continental region believed today to have been created during the Silurian by extensive volcanism. When these two continents joined together, Laurasia was nearly reformed, and by the beginning of the Triassic, the East China craton had rejoined the redeveloping Laurasia as it collided with Gondwana to form Pangaea. North China became, as it drifted southwards from near-Arctic latitudes, the last continent to join with Pangaea.

Final split

Around 200 million years ago, laurasia started to break up. Between eastern North America and northwest Africa, a new ocean formed - the Atlantic Ocean, though Greenland (attached to North America) and Europe were still joined together. The separation of Europe and Greenland occurred around 55 million years ago (at the end of the Paleocene). Laurasia finally divided into the continents after which it is named: Laurentia (now North America) and Eurasia (excluding the Indian subcontinent).

North America Continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere

North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere; it is also considered by some to be a northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the southeast by South America and the Caribbean Sea.

Africa The second largest and second most-populous continent, mostly in the Northern and Eastern Hemispheres

Africa is the world's second largest and second most-populous continent, being behind Asia in both categories. At about 30.3 million km2 including adjacent islands, it covers 6% of Earth's total surface area and 20% of its land area. With 1.2 billion people as of 2016, it accounts for about 16% of the world's human population. The continent is surrounded by the Mediterranean Sea to the north, the Isthmus of Suez and the Red Sea to the northeast, the Indian Ocean to the southeast and the Atlantic Ocean to the west. The continent includes Madagascar and various archipelagos. It contains 54 fully recognised sovereign states (countries), nine territories and two de facto independent states with limited or no recognition. The majority of the continent and its countries are in the Northern Hemisphere, with a substantial portion and number of countries in the Southern Hemisphere.

Atlantic Ocean Ocean between Europe, Africa and the Americas

The Atlantic Ocean is the second largest of the world's oceans, with an area of about 106,460,000 square kilometers. It covers approximately 20 percent of the Earth's surface and about 29 percent of its water surface area. It separates the "Old World" from the "New World".

See also

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Forgotten Continent may refer to:

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