I've heard this explanation for the death of the dinosaurs (and not the small mammals) and for the last Biblical plague. Hear me out!

The theory on the dinosaurs is that when the asteroid hit, it pulverized so much limestone or something like that, that a cloud of CO2 went around the globe close to the ground and got the dinosaurs but not small mammals that were up in trees--or something like that.

The theory on the firstborn of Egypt dying in the last plague was that the firstborn sons slept on special beds that were extra low to the ground, unlike everybody else. So the low cloud of CO2 from the eruption of Santorini (or some such) got the firstborn sons and no one else.