Despite the Age of Enlightenment really having taken hold of Western Civilization by the end of the 18th century, most western scholars still believed that the Earth was about 6,000 years old, having been created on the evening immediately before October 23, 4004 BC. That was the date pronounced by Archbishop James Ussher in his tome, “Annalium Pars Postierior,” published in 1654. He studied the Old Testament with great care and developed a chronology “proving” that was the great day.
Except for those who take the Christian Bible as literal history, the idea that the Earth was created on a certain date in recent, measurable history seems quaint to us today. Even 6 year olds know that dinosaurs lived millions of years ago, that it took more millions of years for all those fern forests to turn into oil and gas, and that man’s evolutionary ancestors walked the Earth 100s of thousands of years ago. But when did western thinking first begin to understand that the Earth was far, far older than 6,000 years, AND who was responsible for the change? (Islamic super-scholar, Avicenna, and Chinese naturalist, Shen Kuo, both postulated the antiquity of the Earth around 1,000 AD, but their ideas were pretty much unknown in the West until the 19th century.)
We owe our enlightenment on the true age of the Earth and, as significantly, how the Earth changed over those eons, to an unassuming Scotch son of an Edinburgh merchant named James Hutton. “James Who?” you say. And rightly so because few of us have even heard of him, much less understood the profound effect he had on our understanding of the natural world. Make a mental note for later that Hutton’s work was indispensable for Charles Darwin, for the father of modern geology, Charles Lyell, and for more geologists, astrophysicists and astronomers than you can count with a calculator, as we will see.
So who is James Hutton? Hutton was obviously very smart. He studied law for a while, then medicine and earned a medical degree from the University of Leyden. But he was restless. He took over two family farms and studied meteorology and geology to practice scientific farming. Over time he met and befriended the Scottish intelligencia of the second half of the 18th century-Adam Smith, David Hume, Joseph Black and, most importantly, mathematician James Playfair, who became a very close friend and his eventual biographer.
Hutton’s interest in geology grew in the 1760s. He toured northern Scotland studying and cataloging rock formations. In 1767 he became deeply involved in the building of the Forth and Clyde Canal, and studied the rock formations exposed by the construction. Gradually, he began to formulate his ideas why the rocks were they way they were. It took him 20 years to become convinced he knew what actually happened. His greatest breakthrough came when he formulated the concept of "uniformitarianism." He saw that the processes of geology, volcanism, erosion, sedimentation, distortion and uplifting as a recurring, ongoing system, recycling the material of the Earth again and again. In his words, “We find no vestige of a beginning, no prospect of an end.” Now that we understand the Earth far, far better because of Hutton, we know there was a beginning and there will be an end, but the time involved so dwarfs a 6,000 year timeline that Hutton’s statement is correct as a practical matter.
Hutton did not attach a name to the lengthy chronology of geological history. He saw it in many ways as a repetitive cycle rather than a long, long story with parts that repeat often. Playfair once called it “the abyss of time,” but the idea was probably best described when John McPhee called it “Deep Time” in his book about the geology of Nevada and Utah, “Basin and Range.” So Deep Time it is.
In 1785 Hutton and Joseph Black read Hutton’s paper, “Theory of the Earth; or an Investigation of the Laws observable in the Composition, Dissolution, and Restoration of Land upon the Globe” to the Royal Society of Edinburgh. In 1794 and 1795 his 2,100 page, 3 volume dissertation was published and, despite being a bit turgid, seems to have overwhelmed the contrary views. The principal opposing view was that all of the things one could see in rock formations were created in a great world wide flood. Hutton had it bang on, though, explaining sedimentation, metamorphism, molten rock intrusion, volcanoes, distortion of sedimentary layers and rise and fall of mountains. The absolutely necessary corollary to all of this geology was that the Earth was vastly older than then thought. All that erosion, layering, compression, heating, tilting, re-eroding, etc. took a long, long time. We could see how long it took with our own eyes and that implied millions and millions of years. Billions it turned out.
Hutton’s ideas were the basis for the detailed geology studies and highly influential work of Charles Lyell, often regarded as the father of geology. Darwin took Hutton’s book with him for study on the voyage of the Beagle. As Darwin formulated his theory of evolution, he realized that Hutton had shown that evolution had ample time to work its magic, that not just one or two hundred generations of plants and animals had taken place in Earth’s history, but millions, which give tiny genetic changes in each generation time to accumulate and mold major changes in plants and animals. Eventually astronomers and astrophysicists would see the age of the Earth as a marker in the age of the Universe—more billions of years—until today, when we understand that the Universe is about 14 billion years old and that the Solar System, Sun, Earth and all the planets (non-planets like poor Pluto, too) formed about 4.2 billion years ago.
What did Hutton see that convinced him Ussher was wrong?
At river edges exposed in Glen Tilt in northern Scotland Hutton saw sedimentary rocks, metamorphic schists, that had been penetrated by granite. There was no open space in the sedimentary rock that would have allowed the granite to precipitate from water, as was thought until then, so the granite must have forced its way into the existing sedimentary layers as flowing molten rock, and then solidified. For that to have worked, the sedimentary rock must have been deposited in layers over a long period of time and hardened (metamorphosed) from pressure and heat created by masses of overlying rock. Only later could the granite come along and invade the formation. Later he saw the same in rock formations around Edinburgh and in Southwest Scotland.
Granite Intrusion Into Sedimentary Rock
In many places, perhaps first at the Isle of Arran in SW Scotland, he saw what came to be known as Hutton’s Unconformity. He observed layers of sedimentary rock, tilted almost vertically and lying over the TOP of them multiple horizontal sedimentary rock layers. Because the two rocks were of different types, the eroded materials from which they accumulated must have come from different places at different times. The lower layers formed, were heated and compressed over millions of years until they were solid rock. They then were tilted by earth movements until they were mostly vertical, but they were still deep under water. Over time, further sedimentary rock formed in the same way—erosion, deposition in layers, pressure, heating and then rock. After that the whole formation was raised by earth movement to above the surface of the waters and then the edges eroded away so that the whole formation was visible in cross-section. Again, an ages long process, implying multiple cycles of rock building over very long periods of time. Over Deep Time.
Two Views of Siccar Point, Scotland, Observed by Hutton. Photos by Dave Souza on Wikipedia
Today we know that all of these ideas are true, and they neatly explain the geology of the world we live in. We owe it largely to the genius of a modest Scottish scientist, James Hutton. If you are ever in Edinburgh, visit his grave at Greyfriars Kirkyard. He showed us the past (and the future) the Earth really has.