Uniformitarianism is a geological principle that suggests the processes shaping the Earth today have been consistent over time. This means that the same natural laws and processes, such as erosion, sedimentation, and volcanic activity, have operated in the past as they do now. The idea is often summarized by the phrase "the present is the key to the past." This concept was popularized by the geologist James Hutton in the late 18th century and later expanded by Charles Lyell. Uniformitarianism contrasts with catastrophism, which emphasizes sudden, dramatic events like meteor impacts or volcanic eruptions as primary forces of change in Earth's history.