The scientific community has voiced two general concerns about the future of the earth. Climatologists and oceanographers have focused on the changes in our physical environment--changes in the climate, the oceans, and the chemistry of the air we breathe. Environmental biologists, on the other hand, have addressed issues of conservation and the extinction of species. There is increasing evidence that these two broad concerns are intertwined and mutually dependent. Past changes in biodiversity have both responded to and caused changes in Earth's environment. In its discussions of ten key...