Dinosaur-Killing Asteroid Caused Marine Mollusk Extinction--But Not from Ocean Acidification

A massive asteroid slammed into Earth about 66 million years ago, causing the mass extinction of the dinosaurs. But dinosaurs weren't the only ones to disappear. Scientists have found that mollusks may have also vanished after this catastrophic event.

Ammonites were free-swimming mollusks of the ancient oceans, and are common fossils. While they were common in the past, though, they became extinct at the time of the end-Cretaceous asteroid impact, along with more than 90 percent of species of calcium carbonate-shelled plankton.

Interestingly, other groups that did not possess calcium carbonate shells were less severely affected. Going off of this information, researchers believe that ocean acidification may have played a role, which is why they decided to investigate the asteroid impact and its effects on the ocean a bit more closely.

The researchers simulated several acidifying mechanisms, including wildfires emitting CO2 into the atmosphere and vaporization of gypsum rocks leading to sulphuric acid rain, which would have been deposited on the ocean's surface. Both of these mechanisms could have occurred after the impact of an asteroid.

Surprisingly, the acidification levels produced by these mechanisms would have been too weak to cause the disappearance of the calcifying organisms. So if it wasn't ocean acidification, what was it?

The researchers aren't sure. However, they do have some theories. It's possible that intense and prolonged darkness from soot and aerosols may have played a role after the impact. What they are sure about, though, is that ocean acidification didn't cause the mass extinction event.

The findings are published in the journal Proceedings of the National Academy of Sciences.

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