It was the asteroid, not volcanoes

Evidence of ocean acidification provides new insights into the last mass extinction.

Researchers have resolved long-standing uncertainty about what caused the last mass extinction around 66 million years ago, which killed three quarters of the planet’s flora and fauna and wiped out the dinosaurs.

Putting to rest other causal hypotheses, particularly a prominent one about gradual volcanic action, they have confirmed that the impact of the Chicxulub asteroid caused sudden ocean acidification, impacting marine ecosystems and the carbon cycle.

They also find that this plunge in ocean ph, coinciding with the mass extinction known more technically as Cretaceous paleogene (K-PG), explains how biodiversity and marine carbon recycling were so slow to recover.

“For years, people suggested there would have been a decrease in ocean ph because the meteor impact hit sulphurrich rocks and caused the raining-out of sulphuric acid,” says lead author Michael Henehan from Yale University, US, “but until now no one had any direct evidence to show this happened.”

The clue, Henehan and colleagues report in the journal Proceedings of the

National Academy of Sciences, came from foraminifera – tiny plankton that grow a shell from calcium carbonate and have a complete fossil record over hundreds of millions of years.

Records from a shallow marine cave at Geulhemmerberg, in the Netherlands, comprising part of the K-PG boundary, gave insights into the first 100 to 1000 years after the asteroid’s impact, a timeline not available from deep marine records.