Nature’s Clocks by Doug Macdougall

Author:Doug Macdougall [Doug Macdougall]
Language: eng
Format: epub
ISBN: 978-0-520-93344-6
Publisher: University of California Press
Published: 2008-03-26T16:00:00+00:00

CHAPTER SIX

Dating the Boundaries

William Smith is a very common name, and it is likely that there were many William Smiths born in eighteenth-century England. Most of them probably led fruitful lives, worthy of more than passing interest. But, as far as geologists are concerned, there is only one who matters: the William Smith who virtually single-handedly put together the first true geological map of Britain ever produced. The author Simon Winchester wrote a book about Smith and his work, calling it The Map That Changed the World. Smith’s map was the culmination of years of observation and investigation, and it was—and still is—a masterpiece. But it is the concepts behind the map that concern us here, because they relate directly to deep time. James Hutton may have been the man who recognized the immensity of geological time, but William Smith was the person who brought a sense of order to its passing.

The last few chapters have examined how age determinations using radioactive isotopes have quantified the opposite ends of the Earth’s time scale: its beginnings 4.5 billion years ago, established through uraniumlead dating; and the (geologically) short period that immediately precedes the present, encompassing much of human history, established through radiocarbon dating. But we also have a detailed time scale for everything in between. We know, for example, when fish appeared in the sea and when animals climbed out onto the land; we know that about 1 billion years ago, in what is now eastern North America, there was a great mountain range rivaling today’s Himalayas; and we know that an extensive ice age gripped the Earth about 2.3 billion years ago. How have these things been worked out? How did we acquire a detailed time scale that orders important geological events throughout the whole of Earth’s history?

To examine those questions fully, and to provide a background to present-day dating studies, it is useful once again to travel back a few hundred years into the past, to the time before radioactivity was discovered, when the very word geology was not yet in use. It was into this world that William Smith was born, in 1769, to a village blacksmith in England. James Hutton was then forty-three and had not yet formulated his ideas about the Earth’s great age. George III was king, and was having problems with those pesky colonies in North America. As a child, William Smith was aware of none of this, but he was, by all accounts, a good student in school, an avid reader, and keenly interested in rocks, the local landscape, and—fossils.

Fossils, as we will see, played a central role in Smith’s life and his creation of a geological map. When he came into the world, the conventional wisdom about these strange artifacts was in a state of flux. For centuries it had been thought—at least in England—that fossils were clever imitations of living creatures, made by an omnipotent Creator either to confuse or to impress ordinary humans, depending on your point of view. Or at least that was the idea espoused by most religious leaders.

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