the interactions among the spheres have changed the Earth system and the individual spheres. An interaction can take one of many forms. It can be a single event, such as the eruption of a volcano or a flood. It can be a temporary change, such as a cold snap that kills a fruit crop. Or it can be an ongoing, steady process, such as erosion. The idea that Earth is always changing, and that the forces of change at work now are the same as those in the past, is called uniformitarianism.
The theory of evolution is a shortened form of the term “theory of evolution by natural selection,” which was proposed by Charles Darwin and Alfred Russel Wallace in the nineteenth century
