Editing Deep time (section)

== Developments in the 19th century ==
The 19th century saw major expansion in how scientists conceptualized Earth's history, transforming deep time from a radical idea into a foundational principle of geology and evolutionary theory. Building on the foundations laid by James Hutton, several competing theories emerged that attempted to explain the formation of Earth's features over immense timescales.

[[Georges Cuvier]], a pioneer of paleontology, proposed that Earth's history was marked by a series of catastrophic events, each followed by the sudden appearance of new life forms. This theory of [[catastrophism]] suggested a segmented past, rather than a continuous one. [[Adam Sedgwick]], who helped popularize catastrophism in Britain, introduced his student Charles Darwin to his way of thinking—prompting Darwin to later joke that Sedgwick was adept at "drawing large cheques upon the Bank of Time."{{sfn|Darwin|1831}} 

In a competing theory, [[Charles Lyell]] advanced a theory known as [[uniformitarianism]], articulated in his ''Principles of Geology'' (1830–1833). Lyell proposed that slow, gradual processes such as erosion, sedimentation, and volcanic activity had shaped the Earth's surface over vast periods—implying an Earth far older than previously imagined. His view echoed and extended Hutton's original ideas, and positioned deep time as essential to understanding Earth's dynamic systems. 

Darwin, deeply influenced by Lyell's thinking, read ''Principles of Geology'' during his voyage on [[Second voyage of HMS Beagle|''HMS Beagle'']] in the 1830s. Lyell's framing of deep time provided Darwin with the necessary timescale to support his own emerging theory of [[evolution]] by natural selection. Without a vast temporal backdrop, evolutionary change would have seemed implausible. Thus, the acceptance of deep time in geology directly enabled new theories of life's development and diversification.