The most-studied mass extinction in Earth history happened 65 million years ago and is widely thought to have wiped out the dinosaurs. New University of Washington research indicates that a separate extinction came shortly before that, triggered by volcanic eruptions that warmed the planet and killed life on the ocean floor.
The well-known second event is believed to have been triggered by an asteroid at least 6 miles in diameter slamming into Mexico's Yucatn Peninsula. But new evidence shows that by the time of the asteroid impact, life on the seafloor mostly species of clams and snails was already perishing because of the effects of huge volcanic eruptions on the Deccan Plateau in what is now India.
"The eruptions started 300,000 to 200,000 years before the impact, and they may have lasted 100,000 years," said Thomas Tobin, a UW doctoral student in Earth and space sciences.
The eruptions would have filled the atmosphere with fine particles, called aerosols, that initially cooled the planet but, more importantly, they also would have spewed carbon dioxide and other greenhouse gases to produce long-term warming that led to the first of the two mass extinctions.
"The aerosols are active on a year to 10-year time scale, while the carbon dioxide has effects on a scale of hundreds to tens of thousands of years," Tobin said.
During the earlier extinction it was primarily life on the ocean floor that died, in contrast to the later extinction triggered by the asteroid impact, which appeared to kill many more free-swimming species.
"The species in the first event are extinct but the groups are all recognizable things you could find around on a beach today," he said.
Tobin is the lead author of a paper in the journal Palaeogeography, Palaeoclimatology, Palaeoecology that documents results of research conducted in a fossil-rich area on Seymour Island, off the Antarctic Peninsula.
|Contact: Vince Stricherz|
University of Washington