Laurasia (/lɔːˈreɪʒə, -ʃiə/)[1] 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.

[2] Laurentia, Avalonia, Baltica, and a series of smaller terranes, collided in the Caledonian orogeny c. 400 Mya to form Laurussia.

[3] Laurentia, the Palaeozoic core of North America and continental fragments that now make up part of Europe, collided with Baltica and Avalonia in the Caledonian orogeny from c. 430–420 Mya to form Laurussia.

[5] "Laurussia" was defined by Swiss geologist Peter Ziegler in 1988 as the merger between Laurentia and Baltica along the northern Caledonian suture.

[5] These original connections apparently survived through one and possibly even two Wilson Cycles, though their intermittent duration and recurrent fit is debated.

[14] In the reconstruction of some Russian geologists, however, the southern margin (modern coordinates) of Siberia merged with the northern margin of Laurentia, and these two continents broke up along what is now the 3,000 km (1,900 mi)-long Central Asian Foldbelt no later than 570 Mya and traces of this breakup can still be found in the Franklin dike swarm in northern Canada and the Aldan Shield in Siberia.

Other blocks that now form part of southwestern Europe and North America from New England to Florida were still attached to the African-South American margin of Gondwana.

A series of continental blocks,  the Cadomian, Avalonian, Cathaysian, Cimmerian terranes,  broke away from Gondwana and began to drift north.

[21] In the Late Cambrian, the mid-ocean ridge in the Iapetus Ocean subducted beneath Gondwana which resulted in the opening of a series of large back-arc basins.

[21][22] With the Caledonian orogeny completed Laurussia was delimited thus:[23] During the Devonian (416-359 Mya) the combined landmass of Baltica and Avalonia rotated around Laurentia, which remained static near the Equator.

The Laurentian warm, shallow seas and on shelves a diverse assemblage of benthos evolved, including the largest trilobites exceeding 1 m (3 ft 3 in).

The Old Red Sandstone Continent stretched across northern Laurentia and into Avalonia and Baltica but for most of the Devonian a narrow seaway formed a barrier where the North Atlantic would later open.

Low sea-levels during the Early Devonian produced natural barriers in Laurussia which resulted in provincialism within the benthic fauna.

High plankton productivity from the Devonian-Carboniferous boundary resulted in anoxic events that left black shales in the basins of Laurentia.

[24] The subduction of the Iapetus Ocean resulted in the first contact between Laurussia and Gondwana in the Late Devonian and terminated in full collision or the Variscan orogeny in the early Carboniferous (340 Mya).

[30] In the late Carboniferous, Laurussia was centred on the Equator and covered by tropical rainforests, commonly referred to as the coal forests.

[32] The Palaezoic-Mesozoic transition was marked by the reorganisation of Earth's tectonic plates which resulted in the assembly of Pangaea, and eventually its break-up.

East Antarctica was the highest ground within Pangaea and produced sediments that were transported across eastern Gondwana but never reached Laurasia.

[35] During the Neoproterozoic-Early Paleozoic break-up of Rodinia, the opening of the Proto-Tethys Ocean split the Asian blocks – Tarim, Qaidam, Alex, North China, South China – from the northern shores of Gondwana (north of India and Australia in modern coordinates) and the closure of the same ocean reassembled them along the same shores 500–460 Mya resulting in Gondwana at its largest extent.

Lhasa, Burma, Sikuleh, southwest Sumatra, West Sulawesi, and parts of Borneo, broke off during the Late Triassic-Late Jurassic.

The eastern branch of the Paleo-Tethys Ocean, however, remained opened while Siberia was added to Laurussia and Gondwana collided with Laurasia.

Pterosaur diversity reach a maximum in the Late Jurassic—Early Cretaceous and plate tectonic didn't affect the distribution of these flying reptiles.

In the early Eocene, a peak in global warming led to a pan-Arctic fauna with alligators and amphibians present north of the Arctic Circle.

While this group now has a mostly tropical distribution, they originated in the Arctic in the late Eocene c. 35 Mya from where they diversified across Laurasia and farther south across the Equator.