Thus began the next stage of evolution, the Cenozoic era or Age of Mammals. The extinction spasm we are now inflicting can be moderated if we choose. If not, the next century will see the closing of the Cenozoic era and the start of a new one characterized by biological impoverishment. It might appropriately be called the Eremozoic era, the Age of Loneliness. People commonly respond to the evidence of species extinction by entering three successive stages of denial.
Extinction is natural.
Species have been dying out through more than 3 billion years of history without permanent harm to the biosphere. Evolution has always replaced extinct species with new ones. All these statements are true, but with a terrible twist. After the Mesozoic spasm, and after each of the four greatest previous spasms spaced over 400 million years, evolution required about 10 million years to restore the predisaster levels of diversity. Worse, evolution cannot perform as in previous ages if natural environments have been crowded out by artificial ones.