You don't really think that man has the might to send the Earth into a downward spiral do you? We as a species look at everything as related to us. In our time frame in our views of what is hospitable and what is not. We are nothing, we are less than nothing. On a global scale and in geological terms we could set off every bomb on the planet and not even phase it. Would it create difficulties for homo sapiens, yes. Would it change the structure of life on the planet?, yes for a time. Would it change the weather? Yes for a time. Would it sterilize the planet?, no. Would life survive? Absolutely. What effect do you feel the detonation of all warheads on the planet (the maximum that we could do to it that I can think of) would have in a million years? How about 2 million or 10 million? My answer would be none as far as the planet is concerned. Maybe just a change as to who is king of the hill. My point is only that all of this talk of destroying the planet or destroying the ecology is crap. We may be altering it in ways that a determental to us, but to destroy it is impossible, we are simply not smart enough. Think about it.