Nothing is more important in the effort to achieve sustainability than keeping the biosphere and the organisms that compose it healthy. In the past century, especially, human activities have signicantly threatened the biosphere, and there is evidence to suggest that a mass extinction event associated with the beginning of the Anthropocene epoch is under way. Fossil records clearly show ve major extinction events millions of years in the past as illustrated in Figure 13.1.1 The rst of these took place at the end of the Ordovician period 434 million years ago with a loss of an estimated 60% of all marine and terrestrial organisms. The second mass extinction took place in the late Devonian period. The end of the Permian mass extinction 251 million years ago resulted in the extinction of up to 95% of marine species. The mass extinction at the end of the Triassic period extinguished about 80% of all terrestrial quadrupeds. The dinosaurs were wiped out in the end of the Cretaceous mass extinction 65 million years ago.