Geology Reference
In-Depth Information
clearly showed that as the ratio of lead to uranium increased, so
too did the age of the rock. At one thousand, six hundred and
forty
million
years old, the oldest mineral in the data set pushed
Earth-time further back than it had ever been before. At the same
time, an idea of the vast aeons represented by the Precambrian
was beginning to emerge; already it spanned two thirds the total
age of the Earth. With the new dating techniques, Holmes
realised, it was going to be possible to impose an order on the
undivided Precambrian rocks, something geologists had hith-
erto only dreamt of doing. At twenty-one young Arthur Holmes
was starting to build order out of chaos.
There was only one possible flaw - what if some lead was
already present when the uranium started to decay? If that
turned out to be the case then, like the ages based on helium,
his results would be meaningless, only this time they would be
much too old. But that was a question that must await his return
from Mozambique.
