Hutton and Lyell proposed that the geological processes of the Earth are long-term, gradual, and consistent between the past and present. This presents the idea that they could preserve consistent evidence over a long term of what life was like at various points in the past.
Work Step by Step
See p. 464 for this information. You will notice that the work of these two scientists fits together in describing a consistent and long-lasting Earth with a reliable fossil record to interpret.