In the 18th century the calculations of Archbishop James Ussher regarding the age of the earth were still accepted without question. According to Ussher god made the earth at 6pm on the evening of Saturday 22nd October 4004 B.C.
This naive certainty was to become a victim of the Scottish Enlightenment and the brilliant mind of James Hutton.
Having qualified as a medical doctor in 1749 Hutton returned to the family farm in Berwickshire not far from where I am typing this now. He became fascinated with geology and wrote that he had "become very fond of studying the surface of the earth, and was looking with anxious curiosity into every pit or ditch or bed of a river that fell in his way".
In 1788 he presented a paper to the Royal Society of Edinburgh in which he described a continuous cycle in which the surface of the earth is constantly being eroded and the products deposited in the sea. There it is compacted into bedrock and later folded and uplifted by volcanic activity and eventually worn away into sediment once again. He concluded with the memorable phrase that "we find no vestige of a beginning, no prospect of an end.”
He knew that these processes required eons - orders of magnitude greater than Ussher's 6000 years. What he was proposing was "Deep Time".
It was a beautiful idea but also a controversial one and he needed some physical evidence to back it up.
In 1788 Hutton set out on a boat trip down the Berwickshire coast with this friends John Playfair and Sir James Hall. When they came across a location known as Siccar Point Hutton knew he had discovered the proof he had been looking for. He later commented that "the mind seemed to grow giddy by looking so far into the abyss of time".
I visited Siccar Point a few years ago and took this photograph.
What James Hutton had found is a feature that geologists call an "unconformity". The vertical layers of rock are made of sandstones called greywackes. We now know that these were laid down on the floor of the Iapetus Ocean in the Silurian Period around 430 million years ago. These layers were buckled and lifted up by the movement of continental plates. Over the next 65 million years the rock was eroded by wind and tide. It is this gap that is the "unconformity". Layers of mudstone were the first to go leaving behind the divided layers we see in the picture.
During the following geological period of the Upper Devonian 370 million years ago rivers began to deposit the sediment that became the red sandstone lying in horizontal layers above the greywacke. A second lifting event pushed the rocks back above sea level and tilted it into its present position. Erosion then sculpted the formation exposing millions of years of geology.
Siccar Point is to Hutton - the father of modern geology - as the Galapagos Islands are to Darwin. Hutton provided the world with a vision of "Deep Time" and made subsequent ideas about the gradual evolution of species possible.
Evolution is a Fact #21 - Footprints in the Sand
Footprints at Laetoli show our Australopithecus afarensis ancestors were bipedal 3.6 million years ago.
Evolution is a Fact #22 - The Hillocks of Hiss
A vestigial feature if the human ear shared by 10% of the population demonstrates our evolutionary history.
Evolution is a Fact #23 - Faunal Succession
The consistent sequence of fossils found in the rocks can only be explained by evolution.
Evolution is a Fact #24 - The Origin of Your Inner Ear
How the bones that reptiles eat with became the bones that we hear with.