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Re: Mystery of Mass Extinctions Is No Longer Murky

In practical terms I agree, although will point out that life as we know it might be over before that point is reached. However, due to my continuing skepticism re the constancy of atmospheric N through post-Archean time, I don't have your level of certainty.

I don't see what could have happened to the chemically extremely stable nitrogen...

You seem to be saying that even a 97% CO2 atmosphere (er, from some totally hypothetical extraterrestrial CO2 source for example) wouldn't start a runaway on Earth. This aroused my curiosity. Is that what you meant?

Oh, no. I'm saying we have no chance of getting a 97 % CO2 atmosphere unless we somehow dissolve all limestone in the world. Even the worst-case scenario (the whole world turns into a tropical paradise) is about 0.1 %, and that would require a massive methane burp that is, judging from the last 55 million years, not very probable.