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After 150 million years, the most successful empire in the history of Planet Earth finally collapsed 66 million years ago. A five-mile-wide space bomb--there's still disagreement as to whether it was an asteroid or a comet--hit on one of the worst places imaginable--a Yucatan Peninsula high in concentrations of two kinds of elements that are known to have climate-altering capabilities--carbon and sulfur. From the sulfur, life on Earth had to endure periods of acid rain and a decade of intense cold. From the carbon, a decade of intense cold was followed by centuries if not millennia of intense heat.

And now, thanks to a discovery in Hell Creek of a fossilized tsunami junk pile by Robert DePalma, we might have finally found the season in which the northern hemisphere was under when Chicxulub hit. Based on the remains of juvenile sturgeons and paddlefish, DePalma surmised that the fall of the dinosaur empire most likely started in the autumn.

I won't list you the 75% of the plant and animal species that died out in this event, for not only is it long, it's also not detailed among some groups. But when you consider that many climate-sensitive clades, like amphibians, did survive this catastrophe, it'd make sense that Chicxulub most likely hit the Yucatan during the fall, when countless plant and animal species were shutting down for the upcoming winter.

So with that in mind, how different would the outcome of the fall of the dinosaur empire be if Chicxulub hit the Yucatan at a different season--say, for example, summer?

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  • $\begingroup$ The Chicxulub impact has been suggested to have hit in early June, based on preserved plant remains with flowers at the boundary that belong to living genera that only bloom in June/July (early summer). $\endgroup$
    – user2352714
    Mar 20, 2020 at 2:49
  • $\begingroup$ That wasn't what DePalma found with those acipenseriform fish fossils. $\endgroup$
    – JohnWDailey
    Mar 20, 2020 at 3:14
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    $\begingroup$ The effects of the Chicxulub impact lasted not for days and weeks, but for years and decades. $\endgroup$
    – AlexP
    Mar 20, 2020 at 4:19
  • $\begingroup$ @JohnWDailey Checking the actual article, DePalma et al. 2019 say nothing about the season in which the impact happened in either the article or the supplementary information. Acipenseriform fishes are also likely to be poor indicators of season because sturgeon and paddlefishes don't reach maturity for more than a decade (and hence the presence of juveniles is not really season-specific). On the other hand...nature.com/articles/352420a0. $\endgroup$
    – user2352714
    Mar 20, 2020 at 4:57
  • $\begingroup$ @user2352714 "The asteroid had likely struck in the fall, DePalma speculated. He had reached this conclusion by comparing the juvenile paddlefish and sturgeon he’d found with the species’ known growth rates and hatching seasons" $\endgroup$
    – JohnWDailey
    Mar 20, 2020 at 11:38

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The seasons in the northern hemisphere are opposite with those of the south. While in one was fall, in the other it was spring.

And the subsequent dust winter lasted more than 1 season cycle.

Based on the above I suspect there is no big difference in the outcome by just changing the season when the impact happens.

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