You might have thought that these enormous gains to geology, combined with Kelvin’s other myriad contributions to science (he published more than six hundred papers), would have exalted him to the rank of those who have had an everlasting impact—the likes of Galileo and Newton. Sadly, the reality is rather different, and even the fact that Kelvin was equally comfortable in the academic and technical worlds did not help. In 1999 Physics World magazine and Physics Web (an internet publication by the British Institute of Physics) conducted polls in which they asked one hundred leading physicists to name the ten greatest physicists of all time. Kelvin’s name did not feature on either list. At least one of the reasons for this subsequent deterioration in Kelvin’s status concerns the debate over the age of the Earth: We know today that the age of the Earth is about 4.54 billion years. This is about fifty times longer than Kelvin’s estimate! How could he have blundered so badly in a calculation supposedly based on the laws of physics?

Science becomes dangerous only when it imagines that it has reached its goal.

—GEORGE BERNARD SHAW

The debate on the age of the Earth between Kelvin and Thomas Huxley generated considerable scientific and public interest. Few disagreed with the assessment that, if anything, Kelvin’s position had been strengthened somewhat by this war of words. Huxley did raise one point, however, which proved to be particularly perceptive. In effect, it identified the crux of Kelvin’s blunder: