For most of the past 2 million years, the dominant view has been that resources are limited. However, more recently some economists have become wildly optimistic about natural resource depletion. Some view the human economy as being separate from the natural systems and merely use nature as a source of raw materials. Therefore while placing the economy as the highest priority in the hierarchy and view the environment further down. This distorted view may be the basis for these three assumptions. First, resources are not limiting, because when one resource is depleted a substitute can be found. Second, exponential economic growth involving natural resources can continue indefinitely on a finite planet. Lastly, the biospheric life support system will continue to maintain conditions favorable to Homo sapiens regardless of increasing anthropogenic stress.