52 Erosion of the Earth
streambed. As he sifted these tiny rocks between his fingers, he realized that these pebbles
had drifted down this small stream, crashing and breaking into smaller pieces as they went.
They used to sit somewhere up higher on the long ridge before him.
This stream was carrying dirt and rock from hilltop to valley floor. This stream was reshaping the entire hillside—slowly, grain by grain, day by day. Not catastrophically as geologists claimed.
The earth, Hutton realized, was shaped slowly, not overnight. Rain pounding down on
hills pulled particles of dirt and rock down into streams and then down to the plains.
Streams gouged out channels, gullies, and valleys bit by bit, year by year.
The wind tore at hills in the same way. The forces of nature were everywhere tearing
down the earth, leveling it out. Nature did this not in a day, but over countless centuries of
relentless, steady work by wind and water.
Then he stopped. If that were true, why hadn’t nature already leveled out the earth?
Why weren’t the hills and mountains worn down? There must be a second force that builds
up the land, just as the forces of nature tear it down.
For days James Hutton hiked and pondered. What built up the earth? It finally hit him:
the heat of Earth’s core built up hills and mountains by pushing outward.
Mountain ranges were forced up by the heat of the earth. Wind and rain slowly wore
them back down. With no real beginning and no end, these two great forces struggled in dynamic balance over eons, the real time scale for geologic study.
With that great discovery, James Hutton forever changed the way geologists would
look at the earth and its processes, and he completely changed humankind’s sense of the
scale of time required to bring about these changes.
Fun Facts: Millions of years ago flowing water eroded the surface of
Mars, leaving behind the gullies, banks, and dry riverbeds scientists have
found there. Now Mar’s atmosphere is too thin to support liquid water. A
cup of water on Mars would instantly vaporize and vanish, blown away
by the solar winds.
More to Explore
Baxter, Stephen. Ages in Chaos : James Hutton and the Discovery of Deep Time. New
York: Forge Books, 2004.
Geologic Society of London. James Hutton—Present and Future. London: Geologic
Society of London, 1999.
Gould, Stephen. Time’s Arrow, Time’s Cycle: Myth and Metaphor in the Discovery of
Geological Time. Cambridge, MA: Harvard University Press, 1997.
Hutton, James. Theory of the Earth. Whitefish, MT: Kessinger Publishing, 2004.
McIntyre, Donald. James Hutton: The Founder of Modern Geology. Edinburgh, Scotland: National Museum of Scotland, 2002.
Repcheck, Jack. The Man Who Found Time: James Hutton and the Discovery of
Earth’s Antiquity. Jackson, TN: Perseus Books Group, 2003.