Lethally Hot Temperatures During the Early Triassic Greenhouse

Paleogeographic reconstruction of the Early Triassic world (Smithian substage) around 250 million years ago, with
a ‘dead zone’ in the tropics. Presence of marine reptiles (ichthyosaurs), terrestrial tetrapods and fish was almost exclusively in higher latitudes (>30 °N and >40 °S) with rare exceptions. Credit: Yadong Sun, University of Leeds

The end-Permian mass extinction, which occurred around 250 million years ago, wiped out nearly all the world’s species. Typically, a mass extinction is followed by a ‘dead zone’ during which new species are not seen for tens of thousands of years. In this case, the dead zone, during the Early Triassic period which followed, lasted for five million years.

A study jointly led by the University of Leeds and China University of Geosciences (Wuhan), in collaboration with the University of Erlangen-Nurnburg (Germany), shows the cause of this lengthy devastation was a temperature rise to lethal levels in the tropics: around 50-60°C (122-140°F) on land, and 40°C  (104°F) at the sea-surface.

Lead author Yadong Sun, who is based in Leeds while completing a joint PhD in geology, says: “Global warming has long been linked to the end-Permian mass extinction, but this study is the first to show extreme temperatures kept life from re-starting in Equatorial latitudes for millions of years.”

The dead zone would have been a strange world – very wet in the tropics but with almost nothing growing. No forests grew, only shrubs and ferns. No fish or marine reptiles were to be found in the tropics, only shellfish, and virtually no land animals existed because their high metabolic rate made it impossible to deal with the extreme temperatures. Only the polar regions provided a refuge from the baking heat.

Before the end-Permian mass extinction the Earth had teemed with plants and animals including primitive reptiles and amphibians, and a wide variety of sea creatures including coral and sea lillies.

This broken world scenario was caused by a breakdown in global carbon cycling. In normal circumstances, plants help regulate temperature by absorbing carbon dioxide and burying it as dead plant matter. Without plants, levels of carbon dioxide can rise unchecked, which causes temperatures to increase.

Professor Paul Wignall from the School of Earth and Environment at the University of Leeds, one of the study’s co-authors, said: “Nobody has ever dared say that past climates attained these levels of heat. Hopefully future global warming won’t get anywhere near temperatures of 250 million years ago, but if it does we have shown that it may take millions of years to recover.”

References

- Lethally Hot Temperatures During the Early Triassic Greenhouse
http://www.sciencemag.org/content/338/6105/366.abstract

- Tropical collapse caused by lethal heat
http://www.eurekalert.org/pub_releases/2012-10/uol-tcc101712.php

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