Lethal heat turned Earth into ‘broken world’
U. LEEDS (UK) — The “dead zone” period that followed the worst extinction of all time lasted 5 million years because it was simply too hot to survive.
The end-Permian mass extinction, which occurred around 250 million years ago in the pre-dinosaur era, wiped out nearly all the world’s species. Typically, the period during which new species are not seen following a mass extinction lasts for tens of thousands of years—not five million.
The research, published in the journal Science, shows 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.
“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,” says lead author Yadong Sun, who is based at the University of Leeds while completing a PhD in geology.
The study is also the first to show water temperatures close to the ocean’s surface can reach 40°C—a near-lethal value at which marine life dies and photosynthesis stops. Until now, climate models have assumed sea-surface temperatures cannot surpass 30°C. The findings may help understand future climate change patterns. The findings may help understand future climate change patterns.
The “dead zone” period 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 Co2 and burying it as dead plant matter. Without plants, levels of Co2 can rise unchecked, which causes temperatures to increase.
For the study, the most detailed temperature record of the period (252-247 million years ago) to date, Sun collected data from 15,000 ancient conodonts (tiny teeth of extinct eel-like fishes) extracted from two tons 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.
“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,” says co-author Paul Wignall, professor from the School of Earth and Environment at Leeds.
The study is the latest collaboration in a 20-year research partnership between the University of Leeds and China University of Geosciences in Wuhan. It was funded by the Chinese Science Foundation. Researchers from the University of Erlangen-Nurnburg in Germany contributed.
Source: University of Leeds
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