Geologist, chemist, naturalist, and originator of one of the fundamental principles of geology—uniformitarianism, which explains the features of the Earth’s crust by means of natural processes over geologic time, he was the son of a merchant and city officeholder. Hutton’s view was that the world’s geologic phenomena can be explained in terms of observable processes, and that those processes now at work on and within the Earth have operated with general uniformity over immensely long periods of time. Hutton’s ideas were astonishing when viewed in the context of the opinion of his day. By the late 18th century, much knowledge had been gained about rocks, strata, and fossils, but none of this wealth of data had been synthesized into a workable general theory of geology. Such a task was seriously impeded by the still-accepted belief that the Earth had been created only about 6,000 years ago, according to the narrative in the biblical book of Genesis. The world’s sedimentary rocks were believed by some geologists to have been formed when immense quantities of minerals precipitated out of the waters of the biblical flood. Erosional processes had long been recognised, but there was no equivalent explanation for the creation of land surfaces, as opposed to their destruction by erosion. The significance of rock formation by means of volcanism and other heat-generated processes in the Earth’s crust was almost completely unrecognised, as was the existence of igneous rocks in general. Hutton’s ideas were diametrically opposed to much of this contemporary theory. He asserted that many rocks had indeed been formed by sedimentary processes—i.e., that rock particles had been washed off the land into the oceans, had accumulated in beds there, and had solidified into rocks. But he posited that the solidification into rocks was due not to the particles’ simple precipitation out of a watery solution but rather was due to the effects of pressure and heat, an explanation which stands to the present day. Hutton asserted that the wearing down of land surfaces by erosion was countered by the formation of new land surfaces due to volcanism and other processes in which the internal heat of the Earth brought new rock constituents up to the Earth’s surface. These new mountains and other landforms were then in turn eroded and were deposited as sediments in the sea, from which they could be upthrust into new land surfaces by subterranean heat-generated processes. Hutton claimed that the totality of these geologic processes could fully explain the current landforms all over the world, and no biblical explanations were necessary in this regard. Finally, he stated that the processes of erosion, deposition, sedimentation, and upthrusting were cyclical and must have been repeated many times in the Earth’s history. Given the enormous spans of time taken by such cycles, Hutton asserted that the age of the Earth must be inconceivably great.