Geoscience Reference
In-Depth Information
moved to the longer-wavelength (redder) end of the light spectrum.
Edwin Powell Hubble (1889-1953), now immortalised by a telescope
bearing his name, studied these redshifts and so produced the evidence
that led to the theory that the Universe was expanding. Hubble
together with Milton La Salle Humason (1891-1971) calculated the
time that it would take to pull all the Universe back to its starting
point from where it expanded, and found that this would have taken
1,800 million years, which by inference was the age of the Universe.
Computed distances of galaxies became a convenient measure of time.
Hubble and Humason's date was in stark contrast to the timescale
suggested by Sir James Hopwood Jeans (1877-1946) who suggested
that the stars were of enormous age: 70,000,000,000,000 years!
The anomaly between the age based on the expanding Universe
and the age of the Earth was first seriously raised three years before his
death by Willem de Sitter (1872-1934), the Professor of Astronomy at
Leiden, at a British Association for the Advancement of Science meet-
ing. He pessimistically predicted that 'I do not think it will ever be
found possible to reconcile the two time scales'. Two years later he
argued that ideas on stellar evolution needed some revision, and cle-
verly postulated that if the Earth had formed through the collision of
two stars, a concept then in vogue, that the chances of this happening
were far greater when the Universe was small, at a time just before it
had begun to expand. Therefore the age of the Universe and the Earth
were the same, and this assertion was plausible according to de Sitter
given the order of error in the geologists' chronological calculations.
Jeans and his collaborators noted in 1935 that both terrestrial and
astronomical data coalesced on a date of 2,100 million years. So all
seemed to be quite satisfactory.
But by 1947 the accepted lower limit for the age of the Earth, as
determined by the geologists using lead isotope data, and cited by
Holmes, was 3,350 million years, and the difference between this
figure and Hubble's 1,800 million years had increased to an unaccept-
able size. Were the geologists creating trouble again? In the following
decade and a half the astronomers and physicists continued their
