The most likely explanation for the disappearance of up to 90 percent of species 250 million years ago, said David Bottjer, is that "the earth got sick."
Bottjer, professor of earth sciences in the USC College of Letters, Arts and Sciences, leads a research group presenting several new pieces of the P-T extinction puzzle.
Matthew Clapham, a recent Ph.D. graduate of Bottjer's laboratory, has found that species diversity and environmental changes were "decoupled" long before the extinction. Conditions on the planet were deteriorating long before species began to die off, Bottjer said, casting doubt on the meteorite strike theory.
"People in the past used to think this big mass extinction was like a car hitting a wall," he said. Instead, Clapham's interpretation of the geological record shows "millions of years of environmental stress."
Pedro Marenco, a doctoral student in Bottjer's lab, has been testing a leading theory for the P-T extinction: that a warming of the earth and a slowdown in ocean circulation made it harder to replace the oxygen sucked out of the water by marine organisms. According to the theory, microbes would have saturated the water with hydrogen sulfide, a highly toxic chemical.
There are two groups of theorists with respect to the PT Extinction. The first is the more traditional ones that view the event as something that happened slowly and over time. The second group is that of the fast killers: the PT Event was on the order of thousands of years or less. The latter group has a lot of impact theory supporters. The former has a lot of others such as anoxia supporters.
The PT Event was a pretty dramatic one that has many aspects that we are still undecovering. I would hesitate to do what is often done and pronounce that X new evidence completely rewrites and solves EVERYTHING. Such pronouncations tend to come back and bite the prouncer in the kartoosh.
That said, this IS interesting stuff.