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Triassic-Jurassic mass extinction

This event happened in less than 10,000 years. It marks the boundary between these two periods and is one of the biggest mass extinction events over the last 500 million years. It happened 201.3 million years ago and profoundly affected life in the seas, for example, 34% of marine genera disappeared. On land, the crurotarsan archosaurs e.g. Postosuchus and many of the large amphibians became extinct.

A chart of all the mass extinction's over the last 550 million years. The Triassic Jurassic extinction is the bar above the 200.

At least half of the species now known to have been living on Earth at that time went extinct. This event vacated terrestrial ecological niches, allowing the dinosaurs to take up the dominant roles in the Jurassic and then Cretaceous period. Before this, the more prominent dinosaurs were the families such as Coelophysidae, which consisted of dinosaurs such as Coelophysis which grew to about 2 metres long, or the bigger Gojirasaurus, which grew to around 5 metres making it one of the biggest dinosaurs of its time.

There had been suggestions that the end-Triassic mass extinction was caused by one or more asteroid impacts. The target was the Manicouagan crater in Quebec, a multiple-ring structure about 100 km across. It is the earth's sixth-largest impact crater, and so certainly large enough to have generated a global mass extinction. However, it is dated as 213-215 Myr old, some 12 Myr before the T-J boundary, and so had nothing to do with the mass extinction.

The clearest model for the T-J mass extinction is global warming, ocean stagnation, and ocean acidification set in train by massive volcanic eruption. At the end of the Triassic/ Early Jurassic a major rifting event, maybe the largest on Earth ever, was beginning as the continent of Pangea slowly began to break up. One of the largest LIPs of all time, the 6000 km diameter Central American Magmatic Province (CAMP) had began to erupt huge amounts (volume of at least 2,000,000 cubic kilometers) of basalt lavas. Scattered outcrops of the rocks can now be found located around the periphery of the central Atlantic region, for example the flood basalts of the Newark Basin, in the NE of the United States. These enormous volcanic provinces are thought to be the result of decompressive melting associated with rifting.

The eruptions sent huge volumes of sulphur dioxide and carbon dioxide into the atmosphere. The sulphur dioxide caused transitory atmospheric cooling, but the carbon dioxide, as a greenhouse gas, caused longer-term warming. The warming raised atmospheric temperatures by several degrees, and the gases with atmospheric water produced acid rain that killed plants on land, and led to wider terrestrial extinctions. In the oceans, the warming lowered thermoclines and terminated normal ocean mixing, preventing oxygen reaching the sea bed, and leaving to extinctions. Associated ocean acidification also killed species.

The British, and European, Rhaetian documents the last stages of the Triassic, and complete successions pass through the T-J boundary, providing opportunities to explore the mass extinction in detail.

For more information visit:

Wikipedia: Triassic Jurassic Extinction

Bristol: Triassic Jurassic Extinction

New world Encyclopedia: Mass Extinction

Natural History Museum: End-Triassic Mass Extinction

Dicynodon Illustration courtesy of John Sibbick.
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