Extreme heat caused massive die-off 250m yrs ago

London: For five million years after the worst mass extinction in Earth`s history, much of the planet was simply too hot for anything to survive, researchers have revealed.

Experts have long been puzzled by the `broken world` scenario that followed the Permian-Triassic mass extinction 250 million years ago. Up to 96 percent of all marine species and 70 percent of land-dwelling vertebrates were wiped out by the event, which is thought to have been caused by a combination of climate change and volcanic activity. During the long heat wave no forests grew in the tropics, only shrubs and ferns, and shellfish were the only marine creatures left in the oceans. Virtually no land animals existed because their metabolisms would not have withstood such high temperatures and only the Polar Regions offered a habitable refuge from the baking heat. Typically it takes tens of thousands of years for new species to appear after a mass extinction but in the case of the Permian-Triassic event, this `dead zone` lasted an extraordinary five million years and a new study has now indicated why. The reason behind this being the rise in temperature - it rose in the tropics to lethal levels, soaring to 60C on land and 40C in the sea, and prevented life from re-emerging. "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 restarting in equatorial latitudes for millions of years," the Daily Mail quoted lead researcher Yadong Sun from the University of Leeds as saying. According to the researchers, a breakdown in global carbon cycling was responsible for the hothouse conditions. Normally plants help regulate temperature by absorbing carbon dioxide and sealing it away in vegetable matter but without plants, levels of the greenhouse gas rose unchecked, causing temperatures to rise. The scientists collected data from 15,000 conodonts - tiny teeth from extinct eel-like fishes - from rocks in southern China. By studying oxygen atoms in the conodonts, they were able to calculate temperature levels many millions of years ago. "Nobody has ever dared say that past climates attained these levels of heat," Professor Paul Wignall said. "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," he added. ANI