David Lindley, The End of Physics. The Myth of a Unified Theory, 1993. From Chapter 1, Lord Kelvin’s Declaration.
It was Kelvin’s assertion, on the other hand, that the world could be no more that one hundred million years old, a figure he obtained by applying the newly formulated principles of energy conservation and thermodynamics to the present state of the Earth and the Sun. In this matter he opposed not only the geologists but also, later, the biologists. Charles Darwin and his followers wanted more time than Kelvin would allow for natural selection and evolution to raise the human race from its lowly beginnings, and in the first edition of the Origin of Species Darwin attempted to match Kelvin, calculation against calculation, by estimating the age of the Weald, a geological feature in southern England, from contemporary estimates of the rate of erosion. He produced a figure of three hundred millions years, which he found satisfactory to his purposes, but his method was roundly attacked by Kelvin and other physicists, and in the second edition of the book Darwin acceded to their superiority and sheepishly withdrew this number in favor of something closer to Kelvin’s.