Hutton's Theory of the Earth and deep time

In 1788 the Scottish naturalist James Hutton published Theory of the Earth in the Transactions of the Royal Society of Edinburgh, after reading it to the society in 1785. He argued that rocks form in a continuous cycle. Rain, rivers and frost wear down the land, the debris settles on the sea floor, and buried sediments are hardened and then heaved upward by the Earth's internal heat to become new land. The same slow processes seen today, working over immense time, explain the rocks. The paper closed by saying that in the Earth he found no vestige of a beginning, no prospect of an end.¹

Most Europeans of the time reckoned the Earth to be some thousands of years old, a figure drawn from biblical chronology, such as Archbishop Ussher's date of 4004 BCE for creation. Explanations of rocks leaned on sudden catastrophes such as the Flood, or on a universal ocean from which rocks precipitated, a view taught by Abraham Werner. Hutton, a farmer and physician who had studied the erosion of soil, saw evidence of repeated cycles. In 1788 he and his friends John Playfair and James Hall sailed to Siccar Point on the Berwickshire coast, where nearly vertical layers of old rock are capped by gently tilted younger ones. The sight implied an enormous span of time. Playfair later wrote that the mind grew giddy looking so far into the abyss of time.¹²

Hutton's prose was dense, and the theory spread through Playfair's clear Illustrations of the Huttonian Theory of 1802. Charles Lyell's Principles of Geology in the 1830s turned it into the doctrine of uniformitarianism, and Darwin carried Lyell's volumes on the Beagle. Natural selection needs vast spans of time to work. The modern age of the Earth, about 4.54 billion years, was established in 1956 by Clair Patterson from lead isotopes.¹