Geology Reference

In-Depth Information

isotopic constitution of the Earth's primeval lead began to be

modified by addition of lead isotopes generated from urani-

um and thorium'
, Holmes concluded
'that on the evidence at

present available, the most probable age of the Earth is about

3,350 million years'
. It was slowly going up - only another bil-

lion or so to go.

Nier's precise radiometric data had triggered a tremendous

amount of interest amongst geologists, and other workers in

the field recognised the opportunity of taking the 'Age of the

Earth' prize for themselves. Fifty years previously the race to date

the age of the Earth had fallen by the wayside with the discov-

ery of radioactivity, but now it gained momentum again, if with

a smaller field of runners, and Holmes was not the first person

to use Nier's data to try and deduce an age of the Earth. In 1942

a Russian, E. K. Gerling, had attempted it and arrived at a min-

imum value of 3950 million years, but as his work was published

in Russian Holmes and others did not become aware of it

until it was translated into English, years after they had inde-

pendently arrived at their own estimates. Similarly, a German,

Fiesel Houtermans, published his 'age of uranium', which he

found to be 2900 million years, very close to Holmes' value for

the age of the Earth. Although Houtermans acknowledged that

Holmes had published a couple of months before him, because

the techniques they both employed were very similar, the model

they adopted soon became known as the Holmes- Houtermans

model for dating the age of the Earth.

But, although all three came fairly close to the right answer,

they had all made the same fundamental mistake: at the end of

the day neither the Ivigtut nor any other sample of lead found

in the Earth's crust contained the magic primeval lead value.

Nevertheless, the mathematical model they developed to do the

calculations with was elegant and perfectly valid and is essen-