We're all familiar with the standard scenario of how the dinosaurs met their fate. A mountain-sized asteroid crashed into what is now the Yucatan Peninsula, setting off continent-wide forest fires, a nuclear winter, and a mass die-off first of plants, then of plant-eaters, and finally of T. rex and his fellow carnivores.

Geochemist Lee Kump doesn't dispute that an asteroid set off the mass extinction at the end of the Mesozoic Era, but he has a different theory about the mechanism. He thinks a load of superheated toxic metals from the disintegrating asteroid -- copper, chromium, aluminum, mercury and lead -- poisoned the oceans and killed off the plankton.

Ninety-three percent of the nannoplankton that form the basis of the marine food web died off in that disaster, and the rest took 270,000 years to recover. By then, most of the land life was done for, as well.

But the most sobering part of Kump's theory -- and the part which has lessons for us today -- is that it may not require an asteroid impact to poison the oceans. Global warming might be able to do the job just as well by generating large clouds of hydrogen sulfide -- that stinky stuff given off by rotten eggs.

Kump thinks that was what happened during the mass extinction that ended the Paleozoic Era 250 million years ago and made possible the rise of the dinosaurs. That earlier event was even more devastating than the one that did in the dinosaurs, wiping out an estimated 95% of all species alive at that time.

According to Kump, it began when Siberian volcanoes gave off massive amounts of carbon dioxide, warming the oceans so that they could not hold as much oxygen and thereby promoting the growth of bacteria that produce hydrogen sulfide.

In 2005, Kump and his colleagues suggested that the seas might have released huge clouds of hydrogen sulfide that drifted over the continents, poisoning all life in their path. Now their projections are not quite as extreme, but they see even occasional belches of the gas as deadly in the long run.

“It may be that 99.9 percent of the time the atmosphere is perfectly breathable, but then these storms come along and you continue to impose these chronic stresses,” Kump told Discovery News. And he warns that the kind of chronic stresses that did in the primitive reptiles and mammals of the Permian could overwhelm us just as easily.

Painting by Donald E. Davis made available by NASA and is in the public domain. Via Wikimedia Commons