Geoscience Reference
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settled on a range of 20 to 40 million years old, but said that the
24-million-year estimate reached by King in 1893 was probably correct.
Tidal friction
Thomson's final methodology for fixing the age of the Earth appeared
in 1868 in a paper published by the Geological Society of Glasgow, and
it relied on changes in the Earth's shape over time, changes effected by
a lowering of its rate of rotation caused by tidal friction. It was well
known that because of friction on the surface waters as the Earth
spins, tidal waters tend to become banked up and do not act in a
predictable manner normally expected. The Earth, he said, assumed
its flattened spherical shape soon after its formation while it was still
molten. He realised that if one took the present rotation rate of the
Earth, and used this to calculate what the shape of the globe would
have been if this had been the primordial spinning rate, one would
expect a spheroidially flattened globe of a particular shape. This
expected shape he found was not appreciably different from the actual
shape of the globe, and so he deduced that very little time had elapsed
since the formation of our planet. He was however unprepared to give
an actual time limit based on this formulation.
REACTION TO SOLAR HEAT, A COOLING GLOBE AND A
SPINNING SPHERE
Thomson's final contribution to the chronological debate was pub-
lished in America in 1898 in a paper entitled 'The age of the earth as an
abode fitted for life'. This was reprinted in several journals in England
in 1899 and is basically a summation of his ideas. He held on to his
view that the Earth had consolidated no more than 40 million years
previously, and that the Sun was no more than 20 to 25 million years
old. His invocation of a solid cooling Earth was at variance with the
views of other scientists, but not all. Samuel Haughton, who sup-
ported his fellow Irishman's work, applied the cooling method in
1865 and in his Manual of Geology published his calculations in
which he arrived at an estimate of 2,298 million years for the age of
