The principle of uniformitarianism in geology states that the processes shaping the Earth today are the same as those that have occurred in the past. This concept, articulated by James Hutton and later popularized by Charles Lyell, emphasizes that present geological processes, like erosion and sedimentation, can explain the formation of rock layers and geological features over time. Understanding this principle allows geologists to interpret Earth's history and the timing of events through the geologic time scale.