At the start of the nineteenth century the Earth's past was mostly imagined as a history a few thousand years long, shaped by sudden, violent catastrophes — floods, great collapses. This "catastrophist" view fit the short timescale of scripture. The Scottish geologist Charles Lyell (1797–1875) changed this picture at its root.

His "Principles of Geology," published in three volumes from 1830, works out a single powerful principle: "the present is the key to the past." There is no need to invoke extraordinary, unrepeatable catastrophes to explain rocks and landforms; the ordinary processes working before our eyes today — rivers eroding, sediments accumulating, volcanoes, earthquakes raising the land centimetre by centimetre — can, given enough time, build the highest mountains and the deepest valleys. This view is called "uniformitarianism."

The cost of this principle was striking: if mountains formed by such slow processes, the Earth must be not thousands but millions — perhaps hundreds of millions — of years old. Lyell planted in the reader's mind this concept of "deep time," which makes human history look like a single instant.

The greatest heir of this gift of time was Charles Darwin. He took Lyell's book with him on the Beagle voyage; from Lyell he received the vast expanse of time that natural selection needed in order to work. Geology showed that the Earth is an archive recording its own history — layers of rock; modern earth science, the history of climate, and plate tectonics were built on this foundation.