Literature

Here's some good holiday reading - at least this proved to be the case for me!
According to some contemporary Earth scientists, "Kelvin's famous calculations, coupled with denial of observational data, impeded geoscience for ~100 yr." They are referring, of course, to Lord Kelvin"s 1863 calculations of the age of the Earth, based on mathematical modeling of Earth cooling and direct measurements of thermal gradients. As a physicist, Kelvin sought to develop quantitative, rather than qualitative, science and he found himself in conflict with geologists who wanted an Earth with "no vestige of a beginning". Kelvin"s estimate of 24-400 million years was a thorn in their side for over 40 years. The story that has been passed down to modern-day students of Earth history is that Kelvin had overlooked the possibility of another heat source - that of radioactive decay - which was not discovered until 1903. Then, Kelvin was proved wrong and the geologists claimed victory!
Describing this aa a modern myth, England et al. have provided a splendid service to the Earth science community in putting the record straight. They rework the calculations of Kelvin and demonstrate their coherence and rational basis. They also repeat the calculations to incorporate a radiogenic heat energy component, showing that Kelvin's conclusions are unaffected. "Thus, the discovery of radioactivity did not invalidate Kelvin's calculation for the age of the Earth."
How then did the myth come about and why did it persist? The authors suggest two reasons. The first is that the myth was a "good story" for the geologists, convenient for reinforcing the idea that geophysics must be the servant, not the master, of geology. (In another context, we have met the "good story" justification before). The second is the personal influence of Lord Rutherford, who had a humorous anecdote to tell of his encounters with Kelvin. The authors have an astute comment on the way established researchers can promote opinion as science: "It is hard to dissuade aging scientists, as they slip into their anecdotage, from repeating stories that they find amusing, but their younger colleagues must not mistake such stories for the history of science."
The main thrust of England et al's excellent article is that Kelvin's argument was addressed in 1895 by John Perry, who suggested a different physical model for the interior of the Earth. "Instead of focusing on Kelvin's calculations, Perry suggested, one should examine his assumptions." Perry's revised model introduced the concept of convection, which was at that time controversial, because the Earth was considered a solid. However, although Perry did have a valid response to Kelvin, which did allow the Earth to have an age of several billion years, it was not received with approval. This is because the geologists of the day, like Kelvin, also held to a solid Earth. "If Perry's analysis had been absorbed by the scientific community of the day, then the first radiometric ages for the Earth would have come as confirmation of the convective explanation for the Earth's surface heat flux, and the "fixist" view of the Earth, which exerted such a brake on geological progress in the first half of the twentieth century, would have been difficult to sustain."
In one sense, Kelvin's challenge to the geological community was successful. Whereas previously they thought they could invoke as much time as they wanted (drawing on Hutton's view of the cycle of time), the geologists were forced to come to terms with time's arrow and a beginning for Earth history. For this achievement, Kelvin ought to be held in esteem by students of geology, and not dismissed. Paradoxically, the geologists and Kelvin now emerge as both victors and losers!
This controversy illustrates very well the importance of paradigms in science. Kelvin and the geologists held to a fixist Earth; eventually, Perry's concept of convection came to be adopted; and radioactive decay brought significant changes to our understanding of the Earth. We all work with mental models or paradigms, and science can easily become an exercise in finding ways of making available data fit the particular model we are working with. Far better to operate with multiple working hypotheses, so that alternative paradigms can be tested and potentially falsified. This strategy applies just as much to biology as it does to geology. This is where ID should be seen as a stimulus to good science, facilitating the methodology of testing and falsifying paradigms. The real dangers we face today are the dogmatists in science who refuse to allow their own paradigms to be critically appraised.

John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics
Philip England, Peter Molnar, Frank Richter
GSA Today, January 2007, 17(1), 4-9.

Abstract: Many readers know the tale of how William Thomson (later Lord Kelvin) calculated the age of the Earth from physical principles and adhered for over 50 years to an estimate that was far younger than geologists' estimates, despite the virtually unanimous opposition of the geological community of the time. The prevalent version of this tale alleges that the discovery of radioactivity simultaneously provided the demonstration (through radiometric dating) that Kelvin had greatly underestimated the age of the Earth and the explanation of why he was wrong (radioactivity being a source of heat that invalidated Kelvin's calculation). We show this popular story to be incorrect; introducing the known distribution of radioactivity into Kelvin's calculation does not invalidate its conclusion. In 1895, before the discovery of radioactivity, John Perry showed that convection in the Earth's interior would invalidate Kelvin's estimate for the age of the Earth, but Perry's analysis was neglected or forgotten, with the consequence that a powerful argument in favor of mobilism was overlooked during the first few decades of debate about continental drift.

See also:

COMMENT by Anne M. Hofmeister, Robert E. Criss
REPLY by Philip England, Peter Molnar, Frank Richter
GSA Today, July 2007, 17(7), 10-11.

Lord Kelvin's Core Values Defended, by David Coppedge, 2 July 2007.