They are known ominously as the Big Five—the five greatest mass extinctions over the past 500 million years, each of which is thought to have annihilated anywhere from 50 to 95 percent of all species on the planet.
Many unsolved mysteries remain regarding these disasters, perhaps the greatest of which is what caused each of them. But research is uncovering how these extinction events dictated the fate of life on this planet—for instance, determining which animals first crawled onto land and which ruled the oceans.
The main suspects behind these catastrophes seem to come either from above, in the form of deadly asteroids or comets, or from below, in the form of extraordinarily massive volcanism. Occasionally, however, unexpected culprits arise—for instance, otherwise innocuous forests.
My Late Triassic Extinction post is progressing slowly, but surely during class breaks. This class is actually showing more promise. Anyways, the LTE post is getting long and needs to have some more information taken from some books at home and the citations need to be done. Mostly its there. Just not polished (it also needs the purty pix).