I am a theoretical physicist and currently Director of 
December 10, 2009
The age of the Earth-6: A time window opens for natural selection
(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)
For previous posts in this series on the age of the Earth, see here.
In the early 1800s geology became recognized as a formal professional discipline. Societies were formed, university professorships were created, systematic surveys studies began to be done of geological strata, and detailed classifications made. In this period Charles Lyell (1795-1875), with the first volume of his book Principles of Geology (1830), emerged as a leader in the new field. His book was a best seller, selling 15,000 copies in its first edition and going through ten subsequent editions.
He too argued the uniformitarian position that the Earth was extremely old, though not infinite, and that this enormous time was sufficient to produce all geological features through the process of very small but cumulative changes. He argued in favor of the model of actualism, the idea that the present rate of geological change could be assumed to be constant over time and thus could be used to extrapolate backwards to find out when specific geologic features began to be formed. As Lyell put it, "the present is the key to the past" (Jackson, p. 130). Lyell and the other uniformitarians were successful in persuading all but the most religiously hidebound that the Earth was far older than one would calculate using the Bible, and by around 1850 this idea was predominant though, as I discussed in the previous post in this series, not unchallenged.
The importance of this development and its timing cannot be overemphasized. It was during this same period (1830 to 1860) that Charles Darwin and Alfred Russell Wallace were working out their theory of evolution by natural selection. They knew that their proposed mechanism of tiny incremental changes in organisms cumulatively leading to major changes had to be very slow and thus required long times. The rise to dominance of uniformitarian thinking in geology (which argued similarly for tiny changes producing big effects) and the almost unlimited time of existence for the Earth that this model projected would have been enormously liberating for them and allowed them to explore their ideas unfettered by constraints that would have inhibited someone living even just a few decades earlier.
Darwin was given Lyell's book to read on his voyage on the Beagle and it is clear that its ideas deeply influenced him. Lyell became Darwin's good friend and supporter although his religious beliefs prevented him from accepting the godless implications of evolution by natural selection.
Scientific theories are not created in a vacuum. They are strongly influenced by contemporaneous factors. Darwin was fortunate that he was developing his revolutionary theory at a time when the power of religious dogma to limit scientific inquiry was on the wane as science became increasingly decoupled from religion, and the intellectual climate was congenial towards what would in earlier times have been condemned as heresy and perhaps even led to death. He was also fortunate to be the son, grandson, and brother of freethinkers, thus providing him with a personal space of intellectual freedom and support for his heterodox views on the origin of species. The fact that his wife was devoutly religious would have been a hindrance to speaking his mind openly at home but she seems to have confined her concerns to worrying about his physical well-being and immortal soul and not try to influence his scientific work.
Spurred by this openness to the idea of a very old Earth, in the first edition of his Origins (p. 285, 286) Darwin even made a rough estimate of the age of time taken for the 'denudation' (erosion) of a region in Sussex in the south of England known as the Weald, arriving at a figure of 300 million years. This figure must have been reassuring to him, suggesting that he did not have to worry about whether the mechanism of natural selection had sufficient time to work.
(It is not commonly known that Darwin was also an accomplished geologist, developing a keen interest in that subject while still a student and making extensive investigations while undertaking long hikes over the English countryside. Before he published his major work in biology in 1859, he had under his belt a successful theory on the origins of the coral reefs of volcanic islands. He had also published three books on geology: The structure and distribution of coral reefs (1842), Geological observations on the volcanic islands visited during the voyage of H.M.S. Beagle (1844), and Geological observations on South America (1846), all based on his careful observations during his epic voyage.)
The break from biblical chronology triggered by the rise of uniformitarianism also allowed other methods of determining the age of the various geological features to emerge. These involved measuring the rate of sedimentation by which the Earth's crust and river deltas were being formed, the rate of increase of salinity of lakes and oceans, the rate at which the Earth's rotation was slowing due to tidal friction, and the rate at which erosion was creating cliffs, ravines and other steep formations. By calculating the rates at which these phenomena were occurring now and making some assumptions about what their initial states might have been (such as that lakes and oceans may have originally been free of these solutes), people arrived at estimates for the time taken to reach the current state.
All of these methods of calculation gave ages in the ranges of tens of millions and even hundreds of millions of years. Although there was wide disagreement with the ages arrived for each specific feature, people realized that estimating the age of geological features was fraught with imprecision because of the huge uncertainties in making estimates of current rates of erosion and lack of knowledge about the initial conditions and so forth, and so the discrepancies between the various methods, while unsatisfying, did not really constitute a crisis. But what was becoming resoundingly clear was that they were all inconsistent with a 6000 year-old Earth. The Bible had become irrelevant for dealing with this question.
Also, these calculations merely gave the time taken for these features to appear and thus could be considered only as providing lower limits to the age of the Earth, not its actual age, so natural selection still had the freedom to do its slow work in the creation of species, relatively unconcerned by upper limits to the time available.
Next: The Earth starts getting younger again.
(Main sources for this series of posts are The Chronologers' Quest: The Search for the Age of the Earth (2006) by Patrick Wyse Jackson and Lord Kelvin and the age of the Earth by Joe D. Burchfield (1975).)
POST SCRIPT: Trailer for The Greatest Action Story Ever Told
Just in time for the holiday season.
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