Climate cooling associated with sulphur gases directly contributed to dinosaur extinction, says St Andrews University

© James McKay – Creative Commons

Climate cooling associated with sulphur gases directly contributed to the extinction of the dinosaurs, according to research from St Andrews University.

The gases had been ejected into the Earth’s atmosphere after a six-mile-wide asteroid hit what is now the Yucatan Peninsula around 66 million years ago.

This research was carried out in collaboration with Bristol University, Syracuse University, New York and Texas A&M University.

It was published today in the PNAS journal and the consequences of this asteroid impact, known as the Chicxulub impact, has been explored.

The research team found that sulphur gases circulated worldwide for years in the Earth’s atmosphere.

It cooled the climate and contributed to the mass extinction of life.

This extinction event was catastrophic for dinosaurs and other life, but it did also allow for the diversification of mammals, including primates.

Dr Aubrey Zerkle, of the School of Earth and Environmental Sciences at the University of St Andrews, said: "One reason this particular impact was so devastating to life seems to be that it landed in a marine environment that was rich in sulphur and other volatiles.

"The dinosaurs were just really unlucky."

Sulphate aerosols had long been implicated as a primary forcing agent of the mass extinction event, which marked the end of the Cretaceous period and the start of the Paleogene period on Earth, but to what extent was unknown.

The new research was able examine the rare sulphur isotopes in material ejected by the impact and deposited in a nearby sea now represented by rocks found along the Brazos River in the American state of Texas.

Dr James Witts, of the School of Earth Sciences as the University of Bristol, said: "Our data provided the first direct evidence for the massive amounts of sulphur released by the Chicxulub impact.

"It’s amazing to be able to see such rapid and catastrophic global change in the geological record."

Atmospheric sulphur in the stratosphere scattered incoming solar radiation and prolonged planetary-scale cooling for many years after the original impact, causing acid rain and reducing the light available for photosynthesis, which is important for plant life and marine plankton that form the base of the food chain.

Christopher Junium, of the Department of Earth and Environmental Sciences at Syracuse University, said: "The initial effects of the impact were caused by rock dust, soot and wildfires, but the sulphur aerosols extended the time period over which life would have suffered from extreme cooling, reduced sunlight and acidification of the land surface and oceans, and it was this extended duration of cooling that likely played a central role in the severity of the extinction."

The Cretaceous period, the third and final period of the Mesozoic Era, lasted from around 145 to 66 million years ago and featured a warm climate with reptiles and dinosaurs dominating Earth.

Its end was marked by the Cretaceous-Paleogene extinction event, a sudden mass extinction event which also marked the start of the Cenozoic Era in which we are still living within today.

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