5-Million-Year-Long ‘Dead Zone’ Caused By Extreme Heat Followed Largest Extinction Event Ever 250 Million Years Ago

October 19, 2012 in Geology & Climate

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The end-Permian mass extinction event 250 million years ago left a ‘broken world’ where new species weren’t seen for the next five million years. Why this ‘dead zone’ lasted so much longer than other similar periods after mass extinctions had been somewhat unclear. But now new research is strongly suggesting that it was simply too hot for nearly anything to survive.

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Mass extinctions are nearly always followed by a period of tens of thousands of years when no new species emerge, a ‘dead zone’. The dead zone following the Early Triassic period is such an extreme outlier, at five million years long, that researchers have long suspected that there must be some unknown influence at work.

The new research clarifies: “the cause of this lengthy devastation was a temperature rise to lethal levels in the tropics: around 50-60°C on land, and 40°C 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 study is also the first to show that water temperatures close to the ocean’s surface can soar up to 40°C. Those are nearly uniformly lethal levels for marine life. And heat that extreme even stops photosynthesis. Climate modellers have been mistakenly assuming that the temperatures at the surface of the ocean can’t exceed 30°C. These findings should prove very relevant to the prediction of possible future climatic extremes.

“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.”

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The Earth had been practically exploding with new life before the end-Permian mass extinction event, including many early reptiles and amphibians, and a very diverse and wide variety of sea creatures, most of which are now extinct.

“This broken world scenario was caused by a breakdown in global carbon cycling. In normal circumstances, plants help regulate temperature by absorbing Co2 and burying it as dead plant matter. Without plants, levels of Co2 can rise unchecked, which causes temperatures to increase.”

This new research is by far the most detailed record of temperatures ever assembled for this period, 252-247 million years ago.

The researchers gathered data “from 15,000 ancient conodonts (tiny teeth of extinct eel-like fishes) extracted from two tonnes of rocks from South China. Conodonts form a skeleton using oxygen. The isotopes of oxygen in skeletons are temperature controlled, so by studying the ratio of oxygen isotopes in the conodonts he was able to detect temperature levels hundreds of millions of years ago.”

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.”

The new research was just published October 19th in the journal Science.

Source: University of Leeds

Image Credits: Yadong Sun, University of Leeds; University of Bristol

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