In June 1788, Scottish geologist James Hutton took his colleagues John Playfair and James Hall to Siccar Point on the Berwickshire coast. To unenlightened eyes, the rocky promontory would have appeared eternal and unchanging. But Hutton and his fellow travellers knew better. As Playfair later wrote: "The mind seemed to grow giddy by looking so far into the abyss of time."
Visit Siccar Point today and it still appears almost exactly as it did in 1788. Hutton realised that this continuity was an illusion, and that the sequence of events he could read in the rocks spoke of unimaginably slow changes occurring over mind-expanding stretches of time. The "angular unconformity" of rocks layers of varying types and orientation could only have formed over tens of millions of years. It was a crucial piece of evidence in his theory of Earth's gradual evolution and the revolutionary ...
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