… ." After the publication of Charles Darwin's On the Origin of Species in 1859, Thomson saw evidence of the relatively short habitable age of the Earth as tending to contradict Darwin's gradualist explanation of slow natural selection bringing about biological diversity. Thomson's own views favoured a version of theistic evolution sped up by divine guidance. His calculations showed that the Sun could not have possibly existed long enough to allow the slow incremental development by evolution – unless it was heated by an energy source beyond the knowledge of Victorian era science. He was soon drawn into public disagreement with geologists and with Darwin's supporters John Tyndall and T. H. Huxley. In his response to Huxley's address to the Geological Society of London (1868) he presented his address "Of Geological Dynamics" (1869) which, among his other writings, challenged the geologists' assertion that the earth must be vastly old, perhaps billions of years in age. Thomson's initial 1864 estimate of the Earth's age was from 20 to 400 million years old. These wide limits were due to his uncertainty about the melting temperature of rock, to which he equated the Earth's interior temperature, as well as the uncertainty in thermal conductivities and specific heats of rocks. Over the years he refined his arguments and reduced the upper bound by a factor of ten, and in 1897 Thomson, now Lord Kelvin, ultimately settled on an estimate that the Earth was 20–40 million years old. In a letter published in Scientific American Supplement 1895 Kelvin criticized geologists' estimates of the age of rocks and the age of the earth, including the views published by Charles Darwin, as "vaguely vast age". His exploration of this estimate can be found in his 1897 address to the Victoria Institute, given at the request of the Institute's president George Stokes, as recorded in that Institute's journal Transactions. Although his former assistant John Perry published a paper in 1895 challenging Kelvin's assumption of low thermal conductivity inside the Earth, and thus showing a much greater age, this had little immediate impact. The discovery in 1903 that radioactive decay releases heat led to Kelvin's estimate being challenged, and Ernest Rutherford famously made the argument in a 1904 lecture attended by Kelvin that this provided the unknown energy source Kelvin had suggested, but the estimate was not overturned until the development in 1907 of radiometric dating of rocks. The