As many glaciers are melting and icy tundras are decaying, there's an unprecedented amount of woolly mammoth material that's becoming dislodged from the ice. Not just mammoth, but all kinds of fossils from the past. What occurred to me was, had anyone tried to pinpoint the first case of human-induced extinction? What was the first time we as species pushed another one to oblivion? I would argue that's probably going to be one of the defining moral problems of the century, human-induced extinction. And I really wanted to know, when did we first cross that barrier?