I read in Walter Alvarez' book T. Rex and the Crater of Doom that the Earth's collision with the large meteor leading to the K-T extinction catalyzed the reaction of atmospheric oxygen and nitrogen molecules to form nitric oxide, which in turn formed highly corrosive nitric acid when combined with water. In addition the impact is thought to have volatilized huge amounts of sulfur contained in anhydrite, which in turn formed sulfuric acid.

This question refers to a thickness of $\pu{1.8m}$ for the section where iridium could be detected in the K-T boundary, suggesting that the resolution may be too low to note the effects of acid rain following the collision.

Is there evidence in the geological record of the formation of these acid species thought to be associated with the collision, say from deposits and/or effects of the ensuing acid rain?


Estimated sulfur release 325 gigatonnes = 325,000 teragrams. The numbers in this diagram are in teragrams

Sulfur Cycleenter image description here

so the release is $\approx 1000\times $ today's annual sulfur cycle.

I think most of the sulfur compounds would be washed into the ocean and then deposited into sediments. I can't find how much sulfur is currently in the oceans, this article says gigatons (because you can smell it). I also can't find how fast the increased sulfur would be deposited.

Another issue is that, unlike iridium, there is normally a lot of sulfur in marine deposits, so it is hard to distinguish what comes from Chicxulub.

  • $\begingroup$ Excellent, thank you! The original article estimating volume of ejecta is agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GL074879. I don't have access right now but the supporting info is also useful. I'll have to look to see if there is reference to the formation of nitric acid in the introduction or discussion. $\endgroup$ – Try Hard Feb 27 at 7:29
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    $\begingroup$ I'm sort of thinking out loud here. I see that the oceans are 3% sulfate so the increase in sulfur concentration is negligible in the oceans (1.332 billion cubic kilometers ). (Cubic kilometer $\approx$ gigatonne.) $\endgroup$ – Keith McClary Feb 27 at 17:58
  • $\begingroup$ I am also just brainstorming out of curiosity. That does seem like "a drop in the ocean" once you dilute the sulfate in the sea against a background that is over 6 orders of magnitude larger. Sulfates are generally very soluble with some exceptions (Ba, Sr, Ag, Pb) says my solubility table. Maybe some unusual local deposits of these minerals formed. Maybe the fossil record shows evidence of sudden acid precipitation. The article you link to is a good lead... $\endgroup$ – Try Hard Feb 27 at 21:59
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    $\begingroup$ I was able to access the article here: hal.archives-ouvertes.fr/hal-01639659/document $\endgroup$ – Try Hard Feb 28 at 8:58

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