Final answer:
Uniformitarianism is the concept that the same geological processes that occurred in the past are still happening today. It is important in studying historical geology as it helps interpret past events based on present observations.
Step-by-step explanation:
Uniformitarianism is the concept in geology that states that the same slow-moving geological processes that shaped the Earth's surface in the past are still happening today. This principle is important in studying historical geology because it allows scientists to interpret past geological events based on the processes observed in the present. For example, the erosion caused by rivers today can help explain the formation of valleys in the past.