December 14, 2009
The age of the Earth-8: Geologists at loggerheads with physicists
(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.
While Kelvin's estimate of the age of the Earth was interesting in its own right and faced its own supporters and detractors, the undeniably important consequence of his work was that for the first time, pinning down an actual age for the Earth became a question that had the potential to be definitively answered, and this spurred the growth of an entire research area. What Kelvin did that was of immense importance were two things: he demolished the uniformitarians' vague notions of an almost limitless time for the age of the Earth and established the importance of doing precise calculations; and he began the process, and highlighted the importance, of unifying scientific theories in formerly divergent fields, by introducing physics principles into geological studies.
Kelvin had arrived at an age for the Earth that made it very difficult for natural selection to succeed as a mechanism. Then, as now, results from physics tend to be regarded as on a sounder footing than those from other disciplines. Hence those other fields such as geology and paleontology and biology tend to try and conform to the constraints provided by physics, not the other way around. Kelvin's estimate of 100 million years as the upper limit for the age of the Earth became part of the scientific lore and geologists and biologists scrambled to accommodate it by trying to find ways to modify their calculations to be consistent with this upper bound. They had some success since each of these calculations depended on many parameters whose values could not be determined precisely, and so there was some room for flexibility.
As for evolution by natural selection, this low upper limit for the age of the Earth caused serious problems. As a result of Kelvin's and other people's strong criticisms of the idea of an Earth that was hundreds of millions of years old, by the third edition of Origins, Darwin had abandoned his breezy calculation of a 300 million year old timescale for the formation of the Weald, done somewhat casually at a time when such an age seemed reasonable. Meanwhile Wallace published another book in 1880 that suggested that 200 million years was sufficient for evolution to have worked (Jackson, p. 193). By squeezing here and pinching there, it seemed possible (though just barely) to accommodate 100 million years as sufficient for natural selection to work, but only with great difficulty and at the risk of sacrificing plausibility.
By around 1880, an uneasy truce seemed to have been drawn among the physics, geology, and biology communities around a 100 million year old Earth. But it did not last long. Others came along who followed up on Kelvin's methods and using more refined calculations and newer estimates for the parameters involved, arrived at even shorter ages of 40 million and then 20 million years for the age of the Earth. Most important among these was an 1893 calculation by Clarence King, the first director of the US Geological Survey who, again basically using Kelvin's thermal methods, arrived at a figure of 24 million years. In a paper in 1897, towards the end of his long and illustrious career, Kelvin stated his conclusion that the Earth was between 20 and 40 million years old, with King's value of 24 million being likely most correct.
This caused immense problems for the other areas of science. If it was true, then almost all of geology would have to be drastically re-conceptualized and the theory of evolution by natural selection would have to be thrown out the window, to be replaced by some teleological model of directed evolution that implied planning or design or some other form of supernatural intervention.
But geologists had had enough of conforming to the ever-increasing restrictive limits of the physicists and modifying their parameters accordingly. Their discipline had now been around for about a hundred years and the newer generation of younger geologists no longer felt like new kids on the block who could be pushed around so easily by the big physics bullies. They felt that 100 million years was as far as it was reasonable for them to go given their own methods of estimating the ages of geological features based on rates of formation and erosion and sedimentation. They dug in their heels and became more assertive, saying that the laws of geology were firmly enough established to rule out such a young Earth and boldly suggested that it was physics that had gone awry somewhere, even if they could not find fault in its calculations or point out where the problematic assumptions were.
Next: What about biology and natural selection?
(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: If the shoe were on the other foot…
If there is one thing that The Daily Show is particularly good at it is showing how ridiculous something is by reversing roles.
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