How 450mn-yr-old mass extinction is closely linked to climate change

WASHINGTON - Geobiologists at California Institute of Technology have found how the mass extinction that occurred 450 million years ago is linked to a cooling climate.

The mass extinction coincided with a glacial period, during which global temperatures cooled and the planet saw a marked increase in glaciers.

So the team studied the timing and magnitude of the glaciation and how it affected ocean temperatures near the equator.

“Our observations imply a climate system distinct from anything we know about over the last 100 million years,” said Woodward Fischer.

However, “one of the biggest sources of uncertainty in studying the paleoclimate record is that it’s very hard to differentiate between changes in temperature and changes in the size of continental ice sheets,” said Seth Finnegan.

Both factors are equally plausible in having caused the mass extinction but differentiating between the two effects is a challenge because until now, the best method for measuring ancient temperatures has also been affected by the size of ice sheets.

Using a new type of paleothermometer the team developed, the researchers have determined the average temperatures during the Late Ordovician-the first time they have been able to tide over the issue.

“By providing independent information on ocean temperature, this new method allows us to know the isotopic composition of 450-million-year-old seawater,” Finnegan said.

“Using that information, we can estimate the size of continental ice sheets through this glaciation.”

And eventually, the researchers can learn more about what Ordovician climate was like-and how it might have stressed marine ecosystems and led to the extinction.

The team discovered that even though tropical ocean temperatures were higher than they are now, moderately sized glaciers still existed near the poles before and after the mass extinction. But during the extinction intervals, glaciation peaked.

Tropical surface waters cooled by five degrees, and the ice sheets on Gondwana grew to be as large as 150 million cubic kilometers-bigger than the glaciers that covered Antarctica and most of the Northern Hemisphere during the modern era’s last ice age 20,000 years ago.

“Although polar glaciers existed for several million years, they only caused cooling of the tropical oceans during the short interval that coincides with the main pulse of mass extinction,” Finnegan said.

The study is published online in Science on January 27. (ANI)