A Great Mistake Has Been Made - Four Revolutions in the Earth Sciences - page 9

Kelvin estimated the Earth's initial temperature at 7,000°F, the measured melting
point of igneous rocks. A handful of observations suggested that temperature in-
creased with depth by about 1°F for every fifty feet. Having these facts and Four-
ier's mathematics at his command, it was a simple matter for Kelvin, if not for
many others, to calculate that the Earth consolidated 98 million years ago. But giv-
en the lack of precision in his starting numbers, he broadened his estimate to say
thattheEarth'sformation“cannothavetakenplacelessthan20,000,000yearsago,
nor more than 400,000,000 million.” 8 His most probable estimate of the age of the
Sun, 100 million years, lay well within this range, seemingly giving two independ-
ent calculations of the age of the Earth and the solar system. This encouraged him
to declare that he had refuted the “Doctrine of Uniformity.” 9
Kelvin was no doubt vexed to find that geologists took no notice of his calcula-
tions. The latest edition of Lyell's Principles continued to claim that the Earth is a
perpetual-motion machine. A heavier barrage was needed, and, in an 1868 lecture
to the Geological Society of Glasgow titled “On Geological Time,” Kelvin loosed
it. 10
“A great reform in geological speculation seems now to have become neces-
sary,” he began. Oddly, or perhaps sagaciously, instead of attacking the geologists
of his day, Kelvin directed his fire at the long-dead John Playfair, who sixty-six
years earlier had written “Illustrations of the Huttonian Theory of the Earth.” 11
Huttonwasapoorwriter,andhistreatise contained longpassagesfromtheFrench,
so that most geologists had to learn of his views from Playfair. “The statement that
the phenomena presented by the earth's crust contain no evidence of a beginning,
and no indication of progress towards an end,” Kelvin wrote, “is founded upon
what is very clearly a complete misinterpretation of the physical laws under which
all are agreed that these actions take place.” Much of Kelvin's paper was taken
up with a third method of gauging the Earth's age, using the slowing of the Earth
caused by tidal friction with the Moon, which provided another corroboration of
Kelvin's view that the Earth could not have existed indefinitely.
“Odious Spectre”
This was too much for geologists and biologists, both of whom needed more time
than Kelvin would grant. Indeed, in a letter to Alfred Russell Wallace, the co-
discoverer of natural selection, Charles Darwin wrote that in order to explain the
missing links that mark the fossil record he would like to take advantage of the
ample eons before the Silurian period, but “then comes Sir W. Thomson like an