We begin with a look at some of the ‘classical’ questions about the earth: its age, its internal heat, and how rocks may deform. These questions are famous both because they are fundamental and because some great controversies raged during the course of their resolution. In looking at how the age of the earth was first inferred, we soon encounter the question of whether great contortions of the crust happened suddenly or slowly. The fact that the interior of the earth is hot is central, both to the occurrence of mantle convection and geological processes, but also historically because one estimate of the age of the earth was based on the rate at which it would lose internal heat.

Much of my limited knowledge of the history of geology prior to this century comes from Hallam's very readable short book Great Geological Controversies [1]. I make this general acknowledgement here to save undue interruption of the narrative through this chapter. My interpretations are my own responsibility.

Time

The idea that continents shift slowly about the face of the earth becomes differentiated from fantasy only with an appreciation of time. One of the most profound shifts in the history of human thought began about 200 years ago, when geologists first began to glimpse the expanse of time recorded in the earth's crust. This revolution has been less remarked upon than some others, perhaps because it occurred gradually and with much argument, and because the sources of evidence for it are less accessible to common observation than, for example, the stars and planets that measure the size of the local universe, or the living things that are the products of natural selection.