WUHAN, Oct. 19 (Xinhua) -- Chinese, British and German scientists have discovered that the worst extinction of the Earth's history happened because the planet was simply too hot to survive.
The discovery about the end-Permian mass extinction, which wiped out the world's species 250 million years ago and was followed by a "dead zone" of five million years in which the planet welcomed no new species,came in a paper published on Friday in Science, one of world's top scientific journals.
The joint study by the China University of Geosciences in Wuhan, capital of central China's Hubei Province, the University of Leeds in Britain and the University of Erlangen-Nuremburg in Germany, shows the cause of the lengthy devastation was a temperature rise to lethal levels: around 50 to 60 degrees Celsius on land, and 40 degrees Celsius 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," said the lead author, 27-year-old Yadong Sun, who is completing a joint PhD in geology with the China University of Geosciences and the University of Leeds.
According to Sun, this is also the first study to show water temperatures close to the ocean's surface can reach 40 degrees Celsius, a near-lethal level at which marine life dies and photosynthesis stops. Climate modelers had assumed sea-surface temperatures cannot surpass 30 degrees Celsius.
"The findings may help us understand future climate change," he said.
The dead zone was 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 for them to deal with the heat. Only the polar regions provided a refuge from the baking heat.
Before this mass extinction, Earth teemed with plants and animals including primitive reptiles and amphibians, and a wide variety of sea creatures including coral and sea lilies.
The "broken world" scenario was caused by a breakdown in global carbon cycling, according to report author Yan Chunbo, a 28-year-old Ph.D. candidate of the China University of Geosciences.
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, Yan explained.
The study is the most detailed temperature record of this study period (252 to 247 million years ago) to date, said Lai Xulong, a professor at the China University of Geosciences and one of the study's co-authors.
Sun and his colleagues collected data from 150,000 ancient conodonts (tiny teeth of extinct eel-like fish) located in two tonnes of rocks from South China. By studying the ratio of oxygen isotopes in the conodonts, they were able to detect temperature levels hundreds of millions of years ago.
"Nobody has ever dared to say that past climates attained these levels of heat. Hopefully, future global warming won't get anywhere near the temperatures of 250 million years ago, but if it does we have shown that it may take millions of years to recover," said Paul Wignall, professor of the School of Earth and Environment at the University of Leeds and another of the study's co-authors.
The study, funded by the Chinese Science Foundation, is the latest collaboration in a 20-year research partnership between the China University of Geosciences and the University of Leeds.