More Chicxulub Results

In the last four decades, we have learned about the Chicxulub impact which seems to have caused a mass extinction and the end of the dinosaurs.  While it is easy to see that being hit by a mile-wide chunk of rock is bad, it has taken some work to figure out just how it could wipe out so many species all around the world, land, sea, and air.

This year, several studies report detailed models of the impact.  A sample core from the Chicxulub crater indicates that the sediments impacted included very large amounts of Sulfur, which would have ejected into the atmosphere and even the stratosphere and above.  In addition to the short term effects, the Sulfur would have been suspended as particulates, with world wide effects on climate akin to a nuclear winter scenario.

This fall, an international team of researchers report a study of fossil records of marine species [1]. These species are highly sensitive to pH, and thus mark the overall acidity of the ocean.  The study shows that populations were stable for 100,000 years (despite the Deccan vulcanism), but plunged dramatically right at the time of the  Chicxulub impact.  This suggests that the massive ejections of Sulfur into the atmosphere led to instant acidification of the ocean from fallout and acid rain.

These findings indicate that there was a massive die off of plankton, which would account for die off of many marine species which depend on them.  It also dramatically changed the Carbon cycle.

The study indicates that surface waters rapidly acidified and rapidly bounced back.  The latter would reflect the lack of plankton which absorb Carbon and Calcium from the water.  Modelling these effects at depths, the researchers hypothesize that the impact caused a substantial reduction, but not a complete collapse of plankton.  The oceans did not recover for 100,000 years or more.

This research does not support hypothesized role of outgassing from the Deccan traps, or any other increase in CO2.  These effects are “overwhelmed by the biogeochemical effect of extinction” ([1], p 3)

These results certainly make sense, especially in light of other recent research.  This is a nice, careful study.  Of course, this is based on limited data, and I can’t evaluate the models in detail.

If these hypotheses hold up, we begin so see that the Chicxulub impact did, indeed, kill off the dinosaurs and many other species.  At least part of the disastrous effect was due to the luck of where the object hit, in shallow water with Sulfur rich sediments.  The research suggests that such an impact would cause massive damage, around the world, and the fallout would cause catastrophic changes to the atmosphere and oceans which cause the extinction of many plankton and plants. Larger animals would quickly starve.

Further, these changes lasted for hundreds of thousands of years.  The Earth did, indeed, recover from this sudden perturbation, but that process took millennia.

---

1. 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, Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact. Proceedings of the National Academy of Sciences:201905989, 2019. http://www.pnas.org/content/early/2019/10/15/1905989116.abstract
2. Lucas Joel, The Dinosaur-Killing Asteroid Acidified the Ocean in a Flash, in New York Times. 2019: New York. https://www.nytimes.com/2019/10/21/science/chicxulub-asteroid-ocean-acid.html