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October 19, 2012
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Deadly heat baked pre-dinosaur world: study
Oct. 19, 2012
Courtesy of the University of Leeds
and World
Science staff
Vicious heat made huge swaths of Earth virtually unlivable for fully five million years following its worst mass extinction, a new study indicates. Artist's concept of the end-Permian extinction, in which 90 percent of all marine species are thought to have perished.
(Credit: NASA Lunar & Planetary Inst.)
According to the research, deadly high temperatures simply cleared out the fish from huge areas of ocean and are something worth thinking about as global warming stalks us even today.
Around 250 million years ago the world witnessed the “end-Permian mass extinction,” a disaster that wiped out nearly all species of life. The event also marked the beginning a new geologic period—the Triassic—which witnessed the first dinosaurs, but that was
some 20 million years later.
In stark contrast, the first five million years of the Triassic were a “dead zone,” scientists say. Typically, a mass extinction is followed by a dead zone during which new species aren’t seen for tens of thousands of years, they explain, but in this case the devastation lingered for millions.
The new study indicates a temperature rise to lethal levels in the tropics caused the slow-motion catastrophe. Temperatures were an estimated 50-60 degrees C (up to about 122 degrees F) on land, and 40 degrees C (about 104 degrees F) at the sea surface.
The study is the first to show ocean surface temperatures can go that high at all—something
experts didn’t believe, said Yadong Sun, the study’s lead author, who is based
at the University of Leeds in the U.K. while completing a joint doctorate in geology. Such a temperature nearly stops sea life in its tracks in part because it shuts down photosynthesis, the process by which plants draw energy from sunlight, he added.
The study is published Oct. 19 in the research journal Science.
“Nobody has ever dared say that past climates attained these levels of heat. Hopefully future global warming won’t get anywhere near [that], but if it does...
it may take millions of years to recover,” said earth scientist and study co-author Paul Wignall of the University of Leeds.
“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,” Sun said.
The dead zone would have been a strange world, according to researchers: very wet in the tropics but with almost nothing growing. No
trees to offer a dollop of shade, only shrubs and ferns. No fish or marine reptiles, only shellfish, and virtually no land animals because their high metabolic rate made it impossible to deal with the extreme temperatures. Only the polar regions,
the investigators say, provided a refuge.
The finding, Sun and colleagues added, might help explain a significant dearth of coal deposits known from the Early
Triassic. Coal comes from dead plants.
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 lilies.
Studies have reached differing conclusions regarding whether
heat caused the initial mass extinction of the end-Permian itself.
Be that as it may, Sun and colleagues said the ravaging heat that followed
was likely due to a breakdown in global carbon cycling. Normally, 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.
Sun and colleagues 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, or variants, of oxygen in
the skeletons depend on temperature, so the levels of these
isotopes in the conodonts are believed to give an estimate of ancient temperatures.
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Vicious heat made huge swaths of Earth virtually unlivable for fully five million years following its worst mass extinction, a new study indicates. According to the research, deadly high temperatures simply cleared out the fish from huge areas of ocean and are something worth thinking about as global warming stalks us even today. Around 250 million years ago the world witnessed the “end-Permian mass extinction,” a disaster that wiped out nearly all species of life. The event also marked the beginning a new geologic period—the Triassic—which witnessed the first dinosaurs, but that was about 20 million years later. In stark contrast, the first five million years of the Triassic were a “dead zone,” scientists say. Typically, a mass extinction is followed by a dead zone during which new species aren’t seen for tens of thousands of years, they explain, but in this case the devastation lingered for millions. The new study, led by the University of Leeds in the U.K. and China University of Geosciences, indicates a temperature rise to lethal levels in the tropics caused the slow-motion catastrophe. Temperatures were an estimated 50-60 degrees C (up to about 122 degrees F) on land, and 40 degrees C (about 104 degrees F) at the sea surface. The study is the first to show ocean surface temperatures can go that high at all—something climate modellers didn’t believe, said Yadong Sun, the study’s lead author, who is based in Leeds while completing a joint doctorate in geology. Such a temperature nearly stops sea life in its tracks in part because it shuts down photosynthesis, the process by which plants draw energy from sunlight, he added. The study is published Oct. 19 in the research journal Science. “Nobody has ever dared say that past climates attained these levels of heat. Hopefully future global warming won’t get anywhere near [that], but if it does we have shown that it may take millions of years to recover,” said earth scientist and study co-author Paul Wignall of the University of Leeds. “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,” Sun said. The dead zone would have been a strange world, according to researchers: very wet in the tropics but with almost nothing growing, researchers said. 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. 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. The broken world scenario is believed to have been caused by a breakdown in global carbon cycling. Normally, 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. Sun and colleagues 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, or variants, of oxygen in skeletons are temperature controlled, so by studying the levels in the conodonts he was able to estimate temperature levels hundreds of millions of years ago.