From Deep Time To Evolution

By Mike Reid

WASHline, May 2006

On a mild June day in the year 1788 at Siccar Point on the wind and water-beaten eastern coast of Scotland, something monumental in the history of science occurred. The significance of what happened on that day would not become apparent until many decades later and it is still largely unknown to the general public. But in a moment of discovery that was precursory to the Theory of Evolution and to much of modern science, the Scottish scientist James Hutton found and recognized the significance of the geologic structure that we now call an "unconformity."

To the geologist, an unconformity is a contact between different rock formations that indicates a gap in time. Sedimentary rocks (i.e., rocks that derive mainly from indurated sands and muds) make up the stratified layer cake-like rock masses that one sees today when passing by cliffsides, river valleys, and road cuts. These stratified sequences of sedimentary rocks are pages in the history book of the Earth. Each stratum is a page in the book. An unconformity represents missing pages.

Some unconformities, such as the one that Hutton observed, are dramatic. At Siccar Point, Hutton looked at the side of a cliff and saw that horizontal strata near the upper part of the cliffside laid atop a sequence of steeply tilted strata. The tilted layers were chopped off and caped by the horizontal ones. The compositions of the two rock masses differed too. Hutton knew from work done by the seventeenth century scholar Nicolaus Steno and others that sedimentary rocks are originally laid down horizontally and that rocks lower down in the stratigraphic sequence are older. Therefore, these tilted rocks had to represent an earlier period of deposition and later uplift. A period of erosion must have followed and chopped off the ends of the tilted strata. The uppermost sequence of horizontal rocks had to have been laid down still later. Hutton correctly recognized that each of the lower layers of rock had once made up the surface of the land or a seafloor and saw that they were the legacies of “a former earth.” Here was his confirmation that the Earth is not static.

By studying rock formations and geologic structures and by carefully noting how water and wind constantly wear away at the land and transport and redeposit the eroded material as sediments, Hutton had theorized that the Earth was a self-recycling machine. He correctly concluded that most sedimentary rocks are the result of earlier episodes of erosion and deposition. Crucially, he observed that erosion and deposition occur very slowly. The layers of sedimentary rocks that make up much of the surface of the Earth simply could not have formed in only a few thousands of years. They had to have taken at least millions of years.

Over the course of several years, Hutton had formulated a hypothesis as to how the Earth worked and had been accumulating facts to support it. But on that day at Siccar Point, he found the crowning piece of hard evidence that he had been seeking that would show that the Earth was far older than was believed at the time. Hutton had found proof of what the twentieth century writer John McPhee (1980) would elegantly term “Deep Time.” It is the concept that the Earth is incomprehensibly ancient. Deep Time refers to an abyss of time that is so immense that it defies the depth of visceral human understanding. Hutton’s discovery of Deep Time would prove crucial to the success of Darwin’s Theory of Evolution and to the further development of the sciences of geology, biology and astronomy in the following century.

In Hutton’s day, around the time of the American Revolution, theologians derived the age of the Earth from biblical studies. The seventeenth century churchman and biblical scholar James Ussher had counted the human generations listed in the Old Testament and had concluded that God created the Earth in the year 4004 BCE. Ussher’s age for the Earth was generally accepted and would remain so into the early nineteenth century. His date for the Creation meant that the Earth was less than six thousand years old. Had Ussher’s value stood, Darwin’s Theory of Evolution would not have been viable. Six thousand years is simply not enough time for Natural Selection to do its work and create the mosaic of life that we know today. Hutton showed that the Earth was indeed old enough for organic evolution to take place. He had no way of knowing how old, but he knew that the then accepted biblically-derived age was no where close. Today, we know from radiometric and other data that the Earth is about 4.6 billion years old — far older than even Hutton could have imagined.

Hutton formulated a magnificent and more or less correct system for the workings of the Earth. He not only discovered Deep Time, but he also developed the rudiments of the rock cycle, which describes how rocks derive from each other in an endlessly renewing cycle. He proposed that the Earth has a hot and molten interior and that “subterraneous fire” is the engine that powers its dynamic system. Hutton concluded that the formation of his former Earths could be explained by geologic processes that are still in operation. This idea that presently active processes can explain the geologic record is now known as the “Principle of Uniformitarianism.” He put all of this together in his wonderful “Theory of the Earth” a synopsis of which he presented in a paper to the Royal Society of Edinburgh in 1788. He laid out his grand theory in detail in a heavy two volume book of the same name published in 1795. However, his weighty and rather turgid writing style made for tedious reading and only an intrepid few delved into his books. A few years after Hutton’s death, his intellectual protege and biographer, John Playfair expounded his theory in a much more concise and readable form in a superb book Illustrations of the Huttonian Theory of the Earth (1802). Most, including Charles Darwin, learned of Hutton’s geology through this work.

Sadly, Hutton’s theory was largely relegated to the fringes of scientific thought until several decades after his death when the eminent British geologist Sir Charles Lyell incorporated it into an updated and more encompassing model. Lyell’s book Principles of Geology (1830) was the standard text book on the Earth sciences for much of the nineteenth century. The young Charles Darwin took Lyell’s book with him on his famous round-the-world voyage. Upon his return to England, he and Lyell became close friends. Had it not been for the understanding of geologic processes and the antiquity of the Earth that he gained from Lyell, Darwin would probably not have been able to make sense of the fossil record which was so crucial to his theory of organic evolution. Without Hutton’s foundational theory, Lyell would not have had a basis upon which to build his system.

Hutton’s influence on the development of the Theory of Evolution might even go beyond the notions of Deep Time and a dynamic Earth. By a remarkable coincidence, Hutton was a friend of Charles Darwin’s grandfather, Erasmus Darwin. Erasmus had ideas on the origins of life that he put forth in poetic writings on the natural world which influenced and eerily foreshadowed those of his more famous grandson (whom he never met). In 1794, Hutton published a massive, but again little-read philosophical treatise titled An Investigation of the Principles of Knowledge. In it he briefly posited a rudimentary, but intriguing idea on the modification of organisms through a mechanism that sounds very much like darwinian natural selection. Perhaps Hutton had discussed this idea with Erasmus and it ultimately made its way to Charles decades later through family memories of his grandfather.

I believe that Hutton’s theory would not have been possible had it not been for the intellectual awakening of the Enlightenment. As long as explanations of the natural world were hamstrung by the need to be consistent with biblical accounts of "The Creation" and an unscientific religion-based cosmology, great advances in human understanding were not possible. Hutton was not a religious man. Far from it. Like many others among the intellectual elite of his day, he was a Deist. Although accepting the idea of a distant, disengaged, and basically unknown supernatural “Creator,” he gave little credence to the Bible as a source information about the natural world. His rejection of traditional religious doctrine freed him to follow the clues of nature wherever they led unconstrained by the fetters of an outdated dogma.

It is regrettable that James Hutton is not better known. He should be. Here is a man who, in my opinion, should be standing shoulder to shoulder with giants such as Isaac Newton and Charles Darwin in the pantheon of history’s most important scientists. Yet unlike these others who are rightly famous, Hutton has languished in undeserved obscurity for more than two centuries. Perhaps his ideas were just too far ahead of their time to gain wider acceptance in his own day. Most of his contemporaries could not countenance an unfathomably ancient Earth and were not ready to discard the Bible as a source of natural knowledge. However, modern scientists, humanists, and rational thinking people owe him a measure of gratitude. In recent years some books on Hutton have come out. It’s about time. Perhaps now, this gentle genius and exemplar of the Scottish Enlightenment will receive some of the recognition that is so long overdue.

Mike Reid is the vice president of WASH and editor of WASHline.