"Lord pity the arse that's clagged to a head that will hunt stones," lamented a rock-hunting, saddle-sore James Hutton. Rock hunting, he had discovered, was punishing work.
In the late 18th century, the educated world clung to the Neptunian theory of the earth proposed by Abraham Gottlob Werner. Known as the father of geology, Hutton overturned the Neptunian orthodoxy and instead proposed his own Plutonian theory of decay and renewal. Hutton could believe in perpetual renewal because of a realization he made: granite is an igneous rock.
The earth has three different kinds of rocks. Igneous rocks are formed from melting rock, such as magma or lava. Sedimentary rocks — home to fossils — are broken down by wind or water into sediments that later solidify. Metamorphic rocks may have started as igneous or sedimentary rocks, but extreme heat or pressure has changed them into something different. In the rocks of Scotland, Hutton found fingers of granite reaching well into sedimentary rocks, and saw this as evidence of subterranean fire and heat. He surmised that the core of the planet could make new rock, offsetting the action of erosion. He also found neatly deposited layers of sedimentary rocks (red sandstone) overlaying rock layers that were almost vertical, as shown in the diagram. The lower layers of rock (greywacke), he concluded, must have been deposited eons before, then later upturned. In these unconformities between rock layers, Hutton saw evidence of vast expanses of time in earth's history. (Charles Lyell was following in Hutton's footsteps when he wrote his own masterwork in 1830.)
Hutton's theory was largely correct, and it was the basis for some exceptionally important theories in geology and biology that followed. Not so well known is that his assertions about the age of the earth were not supported by strong empirical evidence at the time; he proposed his theory of the earth two years before he saw an unconformity. He also proposed a virtually limitless lifespan for our planet, and even though the currently accepted figure of roughly 4.5 billion years is beyond human comprehension, it's not infinite. In the 18th century, neither James Hutton nor anyone else could prove vast expanses of geologic time. Proof of the age of the earth would not come until the 20th century, when chemists learned how to estimate the ages of rocks through rates of radioactive decay.
One of those people lucky enough to be in the right place at the right time, Hutton had the good fortune to be born to an affluent Scottish family whose resources freed him from the obligation to work for a living. Instead, he could spend his time improving his mind. He also got to live in Edinburgh at the very time it was a bright spot in the Enlightenment. Though accused of being irreligious, he was actually a deist who believed that the universe's creator had put into place a perfectly self-sustaining system.
Hutton wasn't so lucky when it came to his writing abilities, which were, in fact, fairly abysmal. In the 1790s, he published a three-volume treatise, over 2,000 pages in length, titled An Investigation into the Principles of Knowledge. According to author Bill Bryson, Hutton's friends encouraged him to expand an earlier paper he had written into a big book, "in the touching hope that he might somehow stumble onto clarity in a more expansive format." It didn't work. In the end, people learned of his ideas mostly from the writings of his good friend John Playfair. A much abler writer, Playfair published Illustrations of the Huttonian Theory of the Earth in 1802. Had Playfair written about one of Hutton's other speculations, Hutton might have trumped Charles Darwin. A careful look at Hutton's work has recently shown his insight. Buried in his intimidating philosophical tome of more than 2,000 pages was a chapter on the origin of natural varieties where Hutton wrote:
If an organised body is not in the situation and circumstances best adapted to its sustenance and propagation, then, in conceiving an indefinite variety among the individuals of that species, we must be assured, that, on the one hand, those which depart most from the best adapted constitution, will be most liable to perish, while, on the other hand, those organised bodies, which most approach to the best constitution for the present circumstances, will be best adapted to continue, in preserving themselves and multiplying the individuals of their race.
What the comma-ridden passage shows is that more than 50 years before the publication of On the Origin of Species, Hutton anticipated Darwin's theory of natural selection. As Darwin learned of others who had suggested the hypothesis before he did, he acknowledged them, but he likely went to his grave not knowing about Hutton's obscure passage.
Narrative text and graphic design © by Michon Scott - Updated June 28, 2012