Uniformitarianism: Charles Lyell
For inspiration, Lyell turned to the fifty-year-old ideas of a Scottish farmer named James Hutton. In the 1790s, Hutton had argued that the Earth was transformed not by unimaginable catastrophes but by imperceptibly slow changes, many of which we can see around us today. Rain erodes mountains, while molten rock pushes up to create new ones. The eroded sediments form into layers of rock, which can later be lifted above sea level, tilted by the force of the uprising rock, and eroded away again. These changes are tiny, but with enough time they could produce vast changes. Hutton therefore argued that the Earth was vastly old a sort of perpetual-motion machine passing through regular cycles of destruction and rebuilding that made the planet suitable for mankind.
Lyell traveled through Europe to find more evidence that gradual changes, the same we can see happening today, had produced the features of the Earth's surface. He found evidence for many rises and falls of sea level, and of giant volcanoes built on top of far older rocks. Processes such as earthquakes and eruptions, which had been witnessed by humans, were enough to produce mountain ranges. Valleys were not the work of giant floods but the slow grinding force of wind and water.
Uniform Processes of Change
Lyell crafted a powerful lens for viewing the history of the Earth. On Darwin's voyage aboard the Beagle, for example, he was able to decipher the history of the Canary Islands (right) by applying Lyell's ideas to the volcanic rock he encountered there. Today satellite measurements reveal that mountains may rise an inch a year, while radioactive clocks help show how they've been rising that way for millions of years. But Lyell could never have grasped the mechanism plate tectonics that makes this kind of geological change happen.
Yet geologists today also know that some of the factors that changed the Earth in the past cannot be seen at work today. For example, the early Earth was pummeled by gigantic hunks of solar debris, some as big as Mars. For the first one or two billion years of Earth's history, plate tectonics didn't even exist as we know it today.
Lyell had an equally profound effect on our understanding of life's history. He influenced Darwin so deeply that Darwin envisioned evolution as a sort of biological uniformitarianism. Evolution took place from one generation to the next before our very eyes, he argued, but it worked too slowly for us to perceive.
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Rock layers image courtesy of David Smith, UCMP; Lyell image courtesy of Dennis O'Neil, Palomar College; Valley image courtesy of David Smith, UCMP; Tenerife, Canary Islands image courtesy of Roberto Bertero.
Understanding Evolution © 2015 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California