| Planet of Weeds |
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The archeological record shows five great extinctions since life began, each representing an evolutionary setback, a wholesale impoverishment of life on the earth. The last of these mass extinctions occurred some 65 million years ago, most likely when an asteroid collided with the earth, spewing vast amounts of dust and debris into the atmosphere. The resultant abrupt cooling obliterated the dinosaurs and at least one fifth of all other extant life forms. We are now in the early stage of the sixth great extinction. Unlike previous ones, which were caused by natural phenomena, this one is of human origin. For the first time in the earth's long history, one species has reached the point where it can eradicate much of life. |
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