The greenhouse extinction

Carbon dioxide is extremely toxic to marine life. It interferes with the biochemistry that many plankton use to build their calcium carbonate shells, and it acidifies the blood. Knoll anti his colleagues proposed that this influx of carbon dioxide was so poisonous that almost everything in the oceans died.

This model, as elegant as it was, didn't say much about what happened to life on land. But our new evidence suggests to me that land animals were also killed by carbon dioxide, although indirectly, Terrestrial plants and animals are far less sensitive to increases in carbon dioxide than marine life, so the change in atmospheric chemistry wouldn't have been able to do any direct harm. But when the gas emerged from the volcanoes and the oceans, though it didn't poison terrestrial life, it did heat up the atmosphere.

The surge in temperature is reflected in the red beds that appear suddenly along the canyon walls of the Caledon River at the P/T boundary. Red beds can be formed when sediments are exposed to the air at high temperature; the iron compounds they contain essentially rust, giving the sediments a ruddy hue. Such red beds are almost unheard of at high latitudes, and their abrupt appearance at the end of the Permian suggests a climate change of massive proportions.

The rapidly changing climate altered weather patterns around the world, and regions that were wet and rainy may have become dry, and vice versa--much as happened this winter during the latest El Nino. Most land animals couldn't survive the change. The few that did, such as the lystrosaurs, seem to have adopted a burrowing habit, not to stave off cold as so many animals do today but perhaps to avoid the heat.

The Permian extinction is now shaping up as an entirely new type of mass extinction. It had nothing to do with extraterrestrial causes, yet it happened far faster than typical extinctions triggered by internal changes to Earth's climate and chemistry. And if our hypothesis is correct, it raises some very disturbing implications about our current situation. We humans are producing carbon dioxide at a prodigious rate, and many climatologists believe that we are already raising temperatures and altering weather patterns. Are we walking down the same path that killed off so much life 250 million years ago--not from carbon dioxide liberated from the oceans but from carbon dioxide liberated by our cars and industry.? There is still far more work to be done and more trips to Africa to be made. But the image of an ancient killer now lies exposed in the red strata of the ancient Karroo desert, a killer I certainly hope is not currently coming back to life after its quarter-billion-year-long sleep.

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