RELIGIOUS ASSUMPTIONS IN LORD KELVIN'S ESTIMATES OF THE EARTH'S AGE
Since Darwin's theory of natural selection challenged Thomson's view of a created universe, Thomson sought to destroy its foundation in uniformitarian geology, which required an indefinitely long age for the earth. In his 1862 paper on the secular cooling of the earth, Thomson assumed an initially hot, molten earth and calculated the time required for the earth to form a crust containing the observed thermal gradient. He excluded from his calculation the total quantity of heat contained within a hot earth. The total heat of the earth would have required much higher estimates of the earth's age. To exclude the earth's interior heat, Thomson assumed that the interior was a rigid solid, in which convection could not occur.
Thomson's fame as a physicist and engineer forestalled examination of his assumptions until 1894 when John Perry demonstrated their arbitrary character. Thomson, then Lord Kelvin, avoided discussion of Perry's criticisms. Instead, in 1897 he accepted an invitation from Sir George Stokes to address the Victoria Institute, an organization devoted to the defense of religion against science. In his address, Kelvin presented a fantastically imagined account of how the originally molten earth had solidified from within outward, intended to isolate the earth's interior heat from the crust and inspired by Kelvin's vision of a created and designed universe.