The principle stating that geological processes taking place on Earth today are the same as those of the past and can be used to describe geological events.

The principle of uniformitarianism describes the fact that the geological processes used to occur in the past were in the same manner and with the same intensity that as they occur in the present on the planet Earth. Therefore, uniformity in the geological processes exhibit from the unknown and unobservable past to present scenario of Earth. The present is the key to the past is the slogan of the principle of uniformitarianism.