William Thomson, who was not to become Lord Kelvin until 1892, began investigating the age of the earth in the 1840s, but only published articles on the subject after Charles Darwin published The Origin of Species in 1859. Thomson rejected Darwin’s uniformitarianism, believing that his own work on thermodynamics showed that the earth must cool and thus change over time. He also rejected natural selection, which he believed entailed a rejection of design in nature.
Thomson marshaled a number of compelling arguments for a relatively young earth, including one based on the age of the sun and another involving the effect of tides on the earth’s rotation. His most famous, however, involved a direct calculation of the age of the earth’s crust based on the assumption that the earth was once molten and had cooled to its present temperature. Based on the available physical and geological data, Thomson concluded in the 1860s that the earth was probably about 100,000,000 years old, a number that most geologists and biologists found plausible and unproblematic. By 1897, after several intermediate estimates, Kelvin had determined that the earth’s crust was about 24,000,000 years old. His research was cited both by non-Darwinian evolutionists such as Lamarckians and by creationists as evidence that the slow process of natural selection was insufficient to account for the diversity of life.
In part because of his preeminence as a physicist, Kelvin’s geochronological work was highly regarded by other scientists. After the discovery that radioactive elements emit heat, however, scientists began to discuss the possibility that the earth and sun are heated by radioactivity, rather than only by initial heat. Kelvin himself admitted that the discovery of radium should affect calculations concerning the age of the earth, although he did not revise his earlier work.
The introduction of radioactivity to geochronology is illustrative of the degree to which the physics of the early twentieth century constituted a scientific revolution. The idea that matter could continuously emit heat violated the principle of conservation of energy, but in 1905 Albert Einstein’s special theory of relativity claimed that matter could be converted into energy. Kelvin, very much a nineteenth century physicist, publicly rejected relativity.
This is based on a little piece of my too-long-for-E2 college honors thesis, George Frederick Wright and the Harmony of Science and Revelation.
Work Cited
- Joe D. Burchfield, Lord Kelvin and the Age of the Earth (Chicago: University of Chicago Press, 1990).
- Stephen Jay Gould, The Structure of Evolutionary Theory (Cambridge, Mass.: Belknap, 2002).
- A. Hallam, Great Geological Controversies, 2nd edition (Oxford: Oxford University Press, 1989).
- Sandra Herbert, Charles Darwin, Geologist (Ithaca, N.Y.: Cornell University Press, 2005).