Final answer:
The principle that 'The present is the key to the past' is known as uniformitarianism, established by Charles Lyell, which suggests that geological processes have remained consistent over time.
Step-by-step explanation:
The statement 'The present is the key to the past' best describes the principle of uniformitarianism. This principle, put forth by Charles Lyell, posits that the geological processes we observe shaping the Earth today have worked in the same way throughout Earth's history. Erosion by rivers, the deposition of sediment, and volcanic activity are examples of processes that have occurred over millions of years, at consistent rates, shaping the Earth's surface. Unlike the law of superposition, which relates to the relative ages of sedimentary layers, or the principle of original horizontality, indicating that layers of sediment were initially deposited flat, uniformitarianism is a broader concept. It provides the framework for understanding how current geological processes can be extrapolated to interpret the geological past. This principle has been fundamental in the study of geology and is encapsulated in the phrase 'The present is the key to the past', indicating that by studying present geological processes, we can infer what the Earth was like in the past.