Laurasia

Laurasia (IPAEng|lɔˈreɪʃiə, lɔˈreɪʒə [OED] ) was a supercontinent that most recently existed as a part of the split of the Pangaean supercontinent in the late Mesozoic era. It included most of the landmasses which make up today's continents of the northern hemisphere, chiefly Laurentia (the name given to the North American craton), Baltica, Siberia, Kazakhstania, and the North China and East China cratons.

The name combines the names of Laurentia and Eurasia.

Origin

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 1 billion 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.

Break up 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. There is no evidence, though, for any large scale Carbonifeous glaciation of the northern continents. This cold period saw the re-joining of Laurentia and Baltica with the formation of the Appalachian Mountains and the vast coal deposits which are today a mainstay of the economy of such regions as West Virginia, the United Kingdom and Germany.

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, Pangaea started to break-up. Between eastern North America and northwest Africa, a new ocean formed - the Atlantic Ocean, even though Greenland (attached to North America) and Europe were still joined together. The separation of Europe and Greenland occurred around 60 million years ago (in the Paleocene). Laurasia finally divided into the continents after which it is named: "Laurentia" (now North America) and "Eurasia" (excluding India and Arabia).

See also

* Alexander du Toit
* Alfred Wegener
* Avalonia

References