
Several times in the distant past, catastrophic extinctions have swept the Earth, causing more than half of all species--from single-celled organisms to awe-inspiring behemoths--to suddenly vanish and be replaced by new life forms. Today the rich diversity of life on the Earth...

Several times in the distant past, catastrophic extinctions have swept the Earth, causing more than half of all species--from single-celled organisms to awe-inspiring behemoths--to suddenly vanish and be replaced by new life forms. Today the rich diversity of life on the Earth...