Doctrine in geology that physical, chemical, and biologic processes now at work on and within the Earth have operated with general uniformity (in the same manner and with essentially the same intensity) through immensely long periods of time and are sufficient to account for all geologic change.
In other words, the present is the key to the past. Although the term is no longer much used, the principle, originated by James Hutton , is fundamental to geologic thinking and underlies the whole development of the science of geology. See also Charles Lyell .