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Politics : The Environmentalist Thread -- Ignore unavailable to you. Want to Upgrade?

To: greenspirit who wrote (20225)	2/11/2008 3:46:14 AM
From: maceng2	Respond to of 36917

How about a change of subject, but "on topic"? telegraph.co.uk it's also in the New Scientist. (if you have access to the site) you can read a sampler here... newscientist.com Bugs poisoned Earth with rotten egg gas By Roger Highfield, Science Editor Last Updated: 6:01pm GMT 06/02/2008 Evidence that the biggest extinction of life in the Earth's history was caused by microscopic life has been found by scientists. Some 251 million years ago, at the end of what is called the Permian period, up to 95 per cent of marine species and 85 per cent of those on land went extinct. Few remark on how the oldest and most successful life forms on Earth - the bacteria and primitive singled-celled creatures called archaea - sailed through virtually unharmed. Now it appears that they played a starring role in the extinctions. advertisement This new view comes from studies of biochemicals that have been trapped inside rocks for billions of years, "molecular fossils" which mean that ancient organisms that otherwise left no trace in the fossil record can now be identified, reports New Scientist. In 2005 Roger Summons, now at the Massachusetts Institute of Technology, teamed up with geochemist Kliti Grice of Curtin University of Technology in Perth, Western Australia. Working with cores of sedimentary rock from China and Western Australia, they identified an interesting organic chemical, a "biomarker", known as isorenieratene. Today, the precursors of this molecule are found only in the pigments of a very specific group of microbes - the green sulphur bacteria. These peculiar microbes make a living by photosynthesis but cannot tolerate oxygen and depend on hydrogen sulphide, the "rotten egg" gas which is highly toxic to plants and animals. The team realised that the presence of these microbes indicated an ocean environment that was shallow enough for light to penetrate and photosynthesis to occur, yet was lacking in oxygen. Instead, it was saturated with hydrogen sulphide: the seas of the late Permian were awash with poison. The team has since found the sulphur bacteria biomarker at a dozen late-Permian sites around the world, good evidence that the hydrogen sulphide oceans were a global phenomenon. Three years ago, Summons, Grice and others combined their biomarker evidence in an influential paper that eliminated asteroids as a suspect for the Permian extinction and pointed the finger at a mass poisoning. A team led by geochemist Lee Kump of Pennsylvania State University in University Park suggested that so much hydrogen sulphide was produced in an ocean devoid of oxygen that it escaped into the atmosphere and poisoned plants and animals, as well as depleting the ozone layer that protects Earth from the sun's harmful UV radiation. "Subsequent work has reduced the predicted severity of these consequences, but release of this toxic gas from the oceans still provides a compelling link between the terrestrial and marine extinctions," says Kump The ultimate culprit was intense global warming triggered by massive emissions of greenhouse gases from one of the largest and most sustained volcanic eruptions ever known, the Siberian Traps. In the hothouse of the late Permian, temperatures at the high latitudes were barely different from those at the equator, currents ground to a halt and the oceans changed, ultimately causing a lethal build-up of hydrogen sulphide produced by bacteria. "Warm water holds less gas (oxygen) that starts the buildup of hydrogen sulphide," explains Kump. "Further eutrophication (buildup of nutrients) intensifies the oxygen depletion and hydrogen sulphide buildup. The buildup of nutrients occurs because the warm, wet climate brings nutrients in from the land with increased river flow."