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I'm sorry, I still don't buy the goats. Comparing the savannah that once occupied the Sahara to the American Great Plains is a bit of a stretch. Humans were introduced to North America at a time when the animals were no longer equipped to deal with that kind of a pack hunter. The bison were about the only ones who were, and that is why the Europeans saw such a homogenous ecosystem when they arrived. And the Dust Bowl was the result of killing off the buffalo (which had been eating the grasses in much the same way as goats) and poor plant-based agricultural practices. And if you want to say that climate had little to do with it, then, by that logic, the American Great Plains should still to this day look more like the Great Sandy Desert... but it doesn't. The Sahara savannah had none of those factors. If anything, it would have appeared most similar to South central Africa, where the animals are VERY well equipped to deal with pre-modern humans.
And, yes, that is one theory that I have read about the P-T extinction as well. The time period over which that occurred doesn't seem definitive, though. Bringing it back to modern times, how much of the CO2 output and levels in the air has to do with the plant life and vegetation that has been lost due to deforestation and other issues (i.e., human over population)?
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