Is preserving the general environmental conditions that allowed civilization to flourish--a moderate climate, a rich array of species, rivers that reach the sea--necessary to ensure humanity endures? Or is minimizing alterations to the global environment introduced by human activity--rising levels of CO2 from fossil-fuel burning, widespread extinction, dams that impound water--more important to our success? Choosing the right approach is vital as the scale of human impact on the planet becomes so large that scientists are calling this new epoch in Earth's history the Anthropocene (when human activity alters global climate and ecosystems).