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 . 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 concept of deep time.
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Little more than a century earlier the Primate of All Ireland, Archbishop James Ussher, had used the Bible and other sources to pinpoint the date of creation to Sunday 23 October 4004 BC. Isaac Newton disagreed: he thought the year was 3988 BC. Then, as now, deep time went deeply against the grain of common sense. “Measuring things against a human lifespan is a normal and natural way to think,” says , an environmental historian at Georgetown University in Washington DC.
Through the heroic efforts of Hutton and many after him, we now know that Earth is around 4.54 billion years old and the universe about 13.8 billion. Our world is almost inconceivably old.
Deep time was central to the development of the historical sciences – geology, evolutionary biology and cosmology – and remains so. “Their ruling ideas absolutely depend on dealing with deep time,” says McNeill. Without it, we can’t appreciate that some processes, whether the weathering of rocks, the evolution of species or the formation of galaxies, generally occur on timescales so slow as to be inappreciable within a human lifespan. “We might be misled into supposing all is stationary, as most people in most cultures have,” says McNeill.
As Playfair found, trying to conceive deep time can induce vertigo, and our odd glimpses of it – ancient fossils dug from geological strata, pictures of star fields from the deep cosmos – can be hard to deal with. But for McNeill it is also liberating. “What it means to me is that we are all part of an unimaginably long chain of being, both human and non-human, and our own travails don’t amount to a hill of beans.”
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This article appeared in print under the headline “How to think about deep time”
