Today we take a break from earth history per se to mention an important anniversary. On this date, March 7, 1785, in some ways, the modern science of geology was born. On this day the first of two papers by James Hutton was read before the Royal Society of Edinburgh, Scotland. The pair of papers was entitled Concerning the Systems of the Earth, its Duration, and Stability. These papers, with little change, formed the core of Hutton’s Theory of the Earth, published in 1795. Many of the ideas first clearly expressed there serve as the basis for modern geology.
He studied unconformities – breaks in the rock record – cross-cutting relationships, and the tilting of formerly horizontal strata to come to his famous conclusion, expressed later by Charles Lyell as “the present is the key to the past,” the idea that processes operating today must have operated in the past, and that they produced the features we see now. Hutton actually said "from what has actually been, we have data for concluding with regard to that which is to happen thereafter."
An important aspect of his conclusion was that while there was much change in earth history, the processes were fundamentally the same, and operated continually. This led to his famous concluding statement, "The result, therefore, of our present enquiry is, that we find no vestige of a beginning,–no prospect of an end." Today we call this uniformitarianism, a big word that just says the processes affecting things on earth happened uniformly over geologic time.
At the time there was plenty of opposition to Hutton’s ideas. Prevailing thought included the catastrophists, who believed that short intense events created the things we see in the rocks, rather than the gradual effects of erosion, deposition, and multiple relatively small tectonic events such as earthquakes. In fact uniformitarianism was sometimes called gradualism.
Hutton was also opposed by the Neptunists, who were in their own fight against the plutonists. Neptunism suggested that everything was formed in the sea, and plutonists said everything came from molten, volcanic origins. Hutton’s ideas allowed for a nice compromise between those two fairly rigid and extreme views, and gave room for both processes and gave both considerable importance.
The ultimate adoption of the concept of gradual change, uniformitarianism, became so well entrenched in geological thought that even into the middle part of the 20th century, the idea of any kind of catastrophe was ridiculed. Consequently when Luis and Walter Alvarez suggested, in 1980, that a catastrophic impact caused the extinction at the end of the Cretaceous Period that wiped out the dinosaurs, there was considerable laughter at the idea. The good news is that the idea was tested scientifically, and the evidence mounted, culminating in the discovery of the “smoking gun” -- a huge crater in the subsurface of Yucatan that has been dated to just the right time.
Today, I would say that geologists firmly believe that uniformitarianism has been the dominant factor in the evolution of planet earth – but there have indeed been some changes in the processes affecting the planet over its 4.6-billion-year life, and there have indeed been some catastrophes too.
But James Hutton first clearly expressed the basic concepts that govern modern geologic thought, on this day back in 1785.
—Richard I. Gibson
Image from Wikipedia (public domain)