Geology Reference
In-Depth Information
1240 million years, already younger than the age of the Earth,
then thought to be at least 1600 million years old, but by allow-
ing for errors on both sides, it was generally considered that
they were of much the same age.
However, as the age of the Earth gradually crept up towards
3000 million and beyond during the 1940s, this di~culty of an
Earth older than the Universe became acute. The problem lay of
course in accurately determining the Hubble constant, but such
confidence was placed in Hubble's data that for years no-one
seriously considered exploring the possibility that it might be
wrong. In 1936 Hubble himself concluded that 'further revision
[of the constant] is expected to be of minor importance', and as
late as 1949 it was considered 'highly improbable' that obser-
vational changes in the value of the Hubble constant would lead
to a resolution of the time scale problem. Indeed, the age of
the Universe was only increased to 1800 million years, by which
time the age of the Earth was almost twice that. The only solu-
tion seriously considered at the time by some astronomers was
to resurrect John Joly's ideas that the law of radioactive decay
had changed with time. If radiometric dates could not be trust-
ed then the age of the Earth was probably much younger than
that estimated by geologists - and anyway everyone knew
that geologists could not count! For years, Holmes and his con-
sistent dating of the Earth continued to be a thorn in the
astronomers' side.
The problem lasted well into the 1950s, when new measure-
ments of the Hubble constant finally extended the age of the
Universe to a point where it was safely older than the age of the
Earth, and for many years after that it was considered to lie in
the 10-15 billion year range. But in 1994 measurements made
from the Hubble space telescope suggested an age as low as
7 billion years for the Universe, causing momentary interest by
the world's press, who questioned the validity of the Big Bang
theory. Today, we accept that the Hubble constant is a very
di~cult value to measure and that no doubt it will continue to
