[olddustytrail]

I don't know, I wasn't there. How old do you think I am?!

Just kidding. I suspect that's an interglacial when you have warming and melting but before the trees have grown back to recapture the co2. But check with an expert if you want a more authoritative answer.

[bee_rider]

I think is is pretty obvious: those were previous species that tried to become industrial, but were killed by Bigfoots. Humans, with our natural tendency toward absolutely slaughtering other species of large mammals, are the first species to escape the Bigfoot trap.