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Permian Extinction Was Beginning Of 5-Million-Year Deadly Heat Wave

October 19, 2012
Paleogeographic reconstruction of the Earth before the end-Permian extinction event 252-247 million years ago. Credit: Wikipedia CC By-SA 3.0

Lawrence LeBlond for redOrbit.com – Your Universe Online

Life about 250 million years ago was hard to come by. In fact, it was nearly non-existent. Scientists, studying why this period, known as the end-Permian event, lasted so long and have found a key ingredient: heat.

Paul Wignall, a paleontologist at England´s Leeds University, and study coauthor, said during the 200,000-year-long Permian extinction the Earth began cooking, with life struggling to thrive, especially at the equator.

The end-Permian event was also met with a large die-off of plants. And with no plants around to consume carbon dioxide (a gas that warms the planet) the earth became “like a runaway greenhouse–it [started] to get out of control,” said Wignall.

While some life survived the Permian extinction–such as snails and clams–the intense heat soon even killed these creatures, leaving the planet a virtual “dead zone” for 5 million years, he said. While dead zones are typically seen after extinction events, they usually only last on a scale of tens of thousands of years. So it was perplexing to find the dead zone from the Permian extinction event lasted on a scale of millions, rather than thousands, of years.

Lead author Yadong Sun, along with Wignall and research partners from China University of Geosciences and University of Erlangen-Nurnburg in Germany, found that the lengthy die-off was due to a temperature rise in the tropics to around 104°F at sea-surface and up to 140°F on land.

“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 Sun, who holds a PhD in geology at Leeds.

This was also the first study to show water temperatures close to the ocean´s surface can reach temperatures of more than 100°F–a temperature at which point marine life cannot thrive and photosynthesis stops. Until now, climate models have only been able to show sea-surface temperatures reaching a maximum of 86°F.

Researchers hope the new findings will help climate forecasters better understand future climate change patterns.

This dead zone would have been a world unlike anything we have seen before. The tropics would have been very wet, but with nearly zero growth. Only shrubs and ferns would exist, and even they would struggle. Marine life would also have been limited to shellfish in the tropics. Land animals would not be able to survive the intense temperatures because their high metabolic rate made it impossible to deal with these extreme temperatures. During this period, only life at the polar regions could flourish.

Before the Permian extinction, the earth was teeming with plants and animals. Land animals included primitive reptiles and amphibians. The sea was also crawling with life, including lilies, corals and other types of marine life. But as the Permian extinction neared, Co2 levels were on the rise, and as plants began to die off, not being able to keep Co2 in check, the planet started baking slowly. As the planet heated up, more and more life went by the wayside. Less plant life meant even more Co2, continuing the vicious cycle for eons.

To figure out why the die-off was so intense and covered such a long span, Sun and colleagues looked at tiny fossils taken from shallow seas in southern China, which at the time of the Permian extinction, would have been the equator.

By studying oxygen isotopes in these fossils, which the researchers note serve as a “reliable” example for seawater temperatures of the time, they found that Permian seas reached 104°F at sea level.

Armed with this information, the researchers are hoping they can answer why it took the Earth so long to recover from the Permian extinction. Apparently the heat had a lot to do with it, they emphasized.

“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,” said Wignall.

To put it in perspective, the planet now is on a path of reaching dangerous temperature levels that could threaten the world´s agricultural resources. The average global temperature has increased 1.4 degrees in the last 130 years, according to NASA’s Goddard Institute for Space Studies. Two-thirds of that warming has happened since 1975.

But that is still a long way off from the sweltering heat found 250 million years ago during the end-Permian event. And for temperatures to reach such staggeringly huge numbers like that again, most of the plant life on Earth would have to be wiped out first–an unlikely scenario based on current models, noted Wignall.

This study, published in the journal Science, was funded by the Chinese Science Foundation.


Source: Lawrence LeBlond for redOrbit.com - Your Universe Online