the concept that the earth's surface was shaped in the past by gradual processes, such as erosion, and by small sudden changes, such as earthquakes, of the type acting today rather than by the sudden divine acts, such as the flood survived by Noah (Genesis 6–8), demanded by the doctrine of catastrophism
uniformitarianism in American English
(ˌjunəˌfɔrməˈtɛriənˌɪzəm)
noun
the doctrine that all geologic changes may be explained by existing physical and chemical processes, as erosion, deposition, volcanic action, etc., that have operated in essentially the same way throughout geologic time