The principle of uniformitarianism in geology is the concept that the natural laws and processes operating today have always operated in the same way in the past, and these processes are sufficient to explain all geological changes observed in Earth’s history. It emphasizes that the present is the key to the past, meaning that by understanding current geological processes, one can interpret past geological events and formations. This principle was first proposed by James Hutton in the late 18th century and later popularized by Charles Lyell.

Uniformitarianism involves several key ideas:

• Natural laws are constant across time and space.
• Geological processes observed now operated similarly in the past.
• Changes typically occur gradually and steadily, although modern interpretations recognize that rates and intensities can vary and that sudden catastrophic events also play a role.
• The Earth’s geological surface evolves in cycles of erosion, sedimentation, and uplift.

The doctrine serves as a foundation for modern geology by allowing scientists to use present-day observations to infer past geological conditions, rejecting supernatural or catastrophic explanations dominant before its introduction.

Uniformitarianism propounds that the Earth’s features are shaped by continuous and consistent processes over immense periods, making the present the key to understanding the geological past.