Deep time

Deep time is the concept of geologic time. The modern philosophical concept was developed in the 18th century by Scottish geologist James Hutton (1726–1797). Modern scientists believe, after a long and complex history of developments, that the age of the Earth is around 4.55 billion years.

Hutton based his view of deep time on a form of geochemistry that had been developed in Scotland and Scandinavia from the 1750s onward. As mathematician John Playfair, one of Hutton's friends and colleagues in the Scottish Enlightenment, later remarked upon seeing the strata of the angular unconformity at Siccar Point with Hutton and James Hall in June 1788, "the mind seemed to grow giddy by looking so far into the abyss of time".

Early geologists such as Nicolas Steno and Horace-Bénédict de Saussure developed ideas of geological strata forming from water through chemical processes, which Abraham Gottlob Werner (1749–1817) developed into a theory known as Neptunism, envisaging the slow crystallisation of minerals in the ancient oceans of the Earth to form rock. Hutton's innovative 1785 theory, based on Plutonism, visualised an endless cyclical process of rocks forming under the sea, being uplifted and tilted, then eroded to form new strata under the sea. In 1788 the sight of Hutton's Unconformity at Siccar Point convinced Playfair and Hall of this extremely slow cycle, and in that same year Hutton memorably wrote "we find no vestige of a beginning, no prospect of an end".

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