Uniformitarianism is the assumption that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past and apply everywhere in the universe. It has included the gradualistic concept that "the present is the key to the past" and is functioning at the same rates. Uniformitarianism has been a key principle of geology and virtually all fields of science, but naturalism's modern geologists, while accepting that geology has occurred across deep time, no longer hold to a strict gradualism.
Uniformitarianism was formulated by Scottish naturalists in the late 18th century, starting with the work of the geologist James Hutton, which was refined by John Playfair and popularised by Charles Lyell's Principles of Geology in 1830. The term uniformitarianism was coined by William Whewell, who also coined the term catastrophism for the idea that the Earth was shaped by a series of sudden, short-lived, violent events.