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Sunday, December 15

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Dialing back the clock with new perspectives

In our last Research Blog, we discussed the sad reality of the contemporary extinctions we are facing—the appropriately named Sixth Mass Extinction. Now, let’s dial back the clock a bit and reconsider some new perspectives on what happened during one of the earlier big ones.

It has been known for some time that the disappearance of the dinosaurs and so much else of the Earth’s biodiversity at the Cretaceous-Paleogene boundary (about 66 million years ago) was caused by the impact of the Chicxulub Asteroid that landed where the northern tip of Mexico’s Yucatan Peninsula now is located. The impact was devastating locally, and the resultant tsunamis were devastating regionally. But the debris plume that developed encircled the Earth for perhaps a decade, completely altering global climate. Biodiversity on Earth was forever changed by an instantaneous event that had profound short and long-term effects. Many of us tend to consider that event in terms of its effects on terrestrial life, especially the doomed dinosaurs (except for the group that eventually became birds!). A new study published this week (see link below), however, focuses on the asteroid’s effects on the world’s oceans. By looking at the levels of the chemical boron in the shells of extinct foraminifera (tiny shelled planktonic creatures), the researchers were able to evaluate the acidity of the oceans in which they lived. Their sampling and calculations revealed that the oceans became dramatically more acidic in a very short time, geologically speaking, after the asteroid struck. And this dramatic change in the oceans’ environment also resulted in a major cataclysm for marine biodiversity.

The connection that struck me the most is that in our current observations and models of future changes in our environment, increasing acidity in our oceans is one of the predominant features of these changes. Watching events such as coral reefs bleaching and dying globally, we now have a window to the past to see what happened the last time the oceans acidified dramatically.

Thanks for reading!

Publication: Michael J. Henehan, Andy Ridgwell, Ellen Thomas, Shuang Zhang, Laia Alegret, Daniela N. Schmidt, James W. B. Rae, James D. Witts, Neil H. Landman, Sarah E. Greene, Brian T. Huber, James R. Super, Noah J. Planavsky, and Pincelli M. Hull. 2019. Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact. Proceedings of the National Academy of Sciences https://doi.org/10.1073/pnas.1905989116

Open-access link to the original article: https://www.pnas.org/content/early/2019/10/15/1905989116

Joe Mendelson, PhD
Director of Research

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