[knuthom]

He contends that debris in the comet’s tail contaminated the atmosphere with a chemical known to cause aggressive behavior

Did he say what the chemical was?

[Wonder Warthog]

"Did he say what the chemical was?"

Probably dihydrogen monoxide--it has all sorts of bad properties, y'know. (Seriously--that was the first question I had on finishing reading the posted article).

[doug from upland]

Saltpeter. :)

[RightWhale]

Did he say what the chemical was?

Yes. I forget, but it is a hormone or neurotransmitter. Eating or breathing it wouldn't do anything but it is worth thinking about these things because obviously our ancestors were doing something back then and we don't have much of a clue what.

[colonialhk]

Beer