It’s easy to mistake rocks as static objects. You could stare at a rock for a few hours, and generally, it will do nothing interesting.
But the truth is, rocks are anything but static; it’s just that their dynamics are hidden by the long spans of time required for them to transform. They erode, they shift, they change, and ultimately, they tell stories. Rocks are the record keeepers of the Earth. As we look downwards, through layer after dusty layer of sediment, we can, in a sense, travel backwards through time.
Rocks provide an extremely revealing way of examining the history of our planet, but it took until the late 18th century for scientists to fully grasp this concept.
In 1785, Scotland was at the forefront of Western science and philosophy, during a period of time later dubbed the Scottish Enlightment. Despite recent advances in naturalism, chemistry, and medical science, people still thought that the earth 6000 years old, an estimate derived from the book of Genesis in the Bible. Most scientists of the time agreed with this. Even Isaac Newton (who died in 1727) accepted the idea of a young Earth.
But not everyone was convinced. One man, James Hutton, had a very different idea.
James Hutton was a Scottish farmer, born in Edinburgh. He had a degree in medicine, but by all accounts, never practiced medicine. Hutton was an amiable and insatiably curious man, and initially applied his mind to developing and optimizing new farming techniques. At the same time, he had a much more ambitious pet-project on his mind – developing a geological theory of the Earth.
Hutton’s theory was based on observations, and asserted that rocks are constantly being formed, shifted and eroded; Hutton further concluded that these natural process likely behave in the same way now as they did thousands, even millions of years ago.
One of the primary pieces of evidence that Hutton used to support his theory is a rock on the east coast of Scotland called Siccar Point. Siccar Point has an unusual structure – it is made up of two distinct layers of different types of sedimentary rocks (Devonian red sandstone, and Silurian greywacke) that contact each-other at a definitive angle.
Hutton concluded that Siccar point could only have been formed by a long sequence of sedimentation (formation of sandstone from small particles), folding and uplift (the buckling and lifting of rock masses over time) and erosion (the breakdown of rock surfaces by weathering), requiring extremely vast amounts of time – amounts far exceeding the mere 6000 year timeline proposed by biblical scholars.
Today, scientists have a variety of tools at their disposal for determining the age of the Earth, including the radiometric dating of fossils. Although Hutton had no access to these types of techniques, he was still able to conclude that the 6000 year idea was incorrect using observations of modern sediments, and deductive reasoning. It is a powerful example of one person’s curiosity and logic overcoming centuries of well-entrenched religious and scientific dogma.
Text and illustrations by Sam MacKinnon, 2014
Carruthers, M. W. (2014). Hutton’s Unconformity. Natural History. 108(5): 86.
Repcheck, J. (2003). The Man Who Found Time: James Hutton and the Discovery of Earth’s Antiquity. Boulder, Colorado: Perseus (Basic Books).