Geology Reference
In-Depth Information
amounts of lead and in my opinion the suggestion that lead formed by
the degradation of uranium has a di¬erent atomic weight from 'ordinary'
lead is contrary to the trend of chemical investigation, and should not be
regarded as established.
Fifty years later Holmes was to recall the occasion:
I was being violently attacked by the reader of a paper who
insisted that the Age of the Earth must be less than 100 mil-
lion years old. In the discussion that followed I had occasion
to refer to the isotopes of lead, then newly discovered. But iso-
topes did not seem to have been heard of in that audience.
The reader of the paper insisted that all atoms of lead must
have the same atomic weight, and I found myself in an exas-
perated minority of one.
This was to be a common occurrence for many years to come.
A few months later the annual meeting of the British
Association was held in Manchester, despite the war, and the
inevitable discussion about the age of the Earth ensued. Chaired
by Rutherford and with Soddy and Joly in the audience, Holmes
again presented his arguments for an Earth at least 1600 mil-
lion years old. Joly, still strongly in favour of his age of the Earth
estimated from the sodium in rivers, recognised the value of
radiometric ages but rejected the uranium-lead method, accept-
ing only the younger dates provided by the helium method. He
argued fiercely in favour of these because they were more in
keeping with his age of the oceans. While Holmes was used to
these arguments and now fully expected all geologists to urge
caution at the idea of the Earth being so ancient, he was not
expecting Soddy of all people to take up a similar position:
It is hoped that geologists would not be in any immediate hurry to
decide between the geological and radioactive estimates of the age of the
Earth. Owing to the element of uncertainty about the initial stages of dis-
integration . . . there might well be unknown factors still to be discovered
su~ciently important to bring the two methods into closer agreement.
Wearily Holmes reflected that there was still a very long way
to go.
