Everybody’s favorite extinction event is the end of the age of the dinosaurs. Like so many popular mystery stories, there are too many clues. (“In the Library with the Candlestick” or maybe “in the Parlor with the Lead Pipe”.) An asteroid (or comet), the Deccan volcanoes, and plenty of less spectacular factors may have played a role.
In recent years, more detailed evidence is accumulating about the Chicxulub impact, which was certainly a very bad day for Dinosaurs and everyone else. (this, this, this, this, this) But massive vulcanism was happening in India at the time, and the climate certainly changed rapidly, which probably involved many interacting factors and feedback loops.
So what happened to the Dinosaurs at the end, at the Cretaceous-Paleogene boundary?
This year an international team of researchers report on detailed modelling of global paleoclimate and the fossil record for this period, in an effort to untangle the multiple events [1].
“That both volcanism and the impact event occurred within several hundred thousand years of the K/Pg extinctions is beyond reasonable doubt.” ([1], p. 1)
As in any good mystery, the solution (or at least our best estimate) depends on timing.
The researchers conclude that the massive Deccan Traps vulcanism started before the K-Pg boundary, and continued throughout and after the impact. However, they find little evidence of extinction or exceptional climate change before the impact.
On the other hand, the impact event created a huge, short lived “nuclear winter”, during which many species died out. This extinction dramatically altered the biology of the Earth and oceans, producing “biologically amplified carbon cycle change “. The effects of the continuing volcanism would have contributed to long recovery from the disaster.
Interestingly, these two catastrophes may have worked against each other, moderating the effects over the next million years. I.e., the impact caused massive global cooling, while the ongoing vulcanism was causing massive global warming.
“Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from post-extinction volcanism.” ([1], p.1)
It goes to show that it’s not necessarily easy to wipe out a whole planet, or expunge all the life on an ocean world like ours.
Obviously, these findings depend on complex models of the Earth, as well as still limited data. This looks pretty solid, but we’ll have to see if additional data or alternative models support these conclusions in the future. The estimates of global temperature and biology are known from a relative few samples, so understanding may change with more data.
My own non-expert caveat is that this sort of modelling can be very sensitive to artifacts such as the granularity of time and space. In other words, if and when we can redo this work at 100 or 1000 times finer grain, the could be surprises (such as, this [3]).
Assuming these results hold up, it looks like the Chicxulub event killed the Dinosaurs, which is surely the most satisfying way conceivable to tap out old T. rex and company.
And, as I have said before, our species, indeed our whole extended family, truly are Children of Chicxulub.
- Pincelli M. Hull, André Bornemann, Donald E. Penman, Michael J. Henehan, Richard D. Norris, Paul A. Wilson, Peter Blum, Laia Alegret, Sietske J. Batenburg, Paul R. Bown, Timothy J. Bralower, Cecile Cournede, Alexander Deutsch, Barbara Donner, Oliver Friedrich, Sofie Jehle, Hojung Kim, Dick Kroon, Peter C. Lippert, Dominik Loroch, Iris Moebius, Kazuyoshi Moriya, Daniel J. Peppe, Gregory E. Ravizza, Ursula Röhl, Jonathan D. Schueth, Julio Sepúlveda, Philip F. Sexton, Elizabeth C. Sibert, Kasia K. Śliwińska, Roger E. Summons, Ellen Thomas, Thomas Westerhold, Jessica H. Whiteside, Tatsuhiko Yamaguchi, and James C. Zachos, On impact and volcanism across the Cretaceous-Paleogene boundary. Science, 367 (6475):266, 2020. http://science.sciencemag.org/content/367/6475/266.abstract
- Lucas Joel, Meteorite or Volcano? New Clues to the Dinosaurs’ Demise, in New York times. 2020. https://www.nytimes.com/2020/01/16/science/dinosaurs-extinction-meteorite-volcano.html
- Jun-xuan Fan, Shu-zhong Shen, Douglas H. Erwin, Peter M. Sadler, Norman MacLeod, Qiu-ming Cheng, Xu-dong Hou, Jiao Yang, Xiang-dong Wang, Yue Wang, Hua Zhang, Xu Chen, Guo-xiang Li, Yi-chun Zhang, Yu-kun Shi, Dong-xun Yuan, Qing Chen, Lin-na Zhang, Chao Li, and Ying-ying Zhao, A high-resolution summary of Cambrian to Early Triassic marine invertebrate biodiversity. Science, 367 (6475):272, 2020. http://science.sciencemag.org/content/367/6475/272.abstract
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