Geology Reference
In-Depth Information
a wide volume of rock eroded from the continents they had
been removed from, they were the most likely to contain average
lead values representative of the Earth's crust. Taking samples
from the floor of the Pacific Ocean, he analysed the lead ratios
and showed that they too fell on the line defined by the five mete-
orites. This finally proved that all had the same age and the Earth
and meteorites were indeed formed at the same time from the
same solar material. It must have been a stunning moment. The
wildest of all wild miracles.
So, according to Patterson, the
'time since the earth attained its
present mass'
was four thousand, five hundred and fifty-five
million years, give or take a few million. Within a month of
Patterson publishing his results, Holmes gave us his last con-
tribution to the age of the Earth debate, in an article entitled
'How Old is the Earth?' In the ten years since he had last esti-
mated the age of the Earth using Nier's data a great many new
analyses of terrestrial leads had become available and, despite
his early work on meteorites, Holmes argued, as others did, that
'to use the isotopic composition of lead from iron meteorites
as part of the basic data for calculating the age of the earth
or its crust, is unsound in principle . . . the correct procedure
is to use terrestrial materials'
. Accordingly he wrote:
'My own
attempt to solve the problem from terrestrial evidence alone
leads to essentially the same result, which may be expressed
as 4,500
±
100 million years',
his larger error encompassing
Patterson's results.
Today Claire Patterson is recognised as the man who finally
dated the age of the Earth, although a new consensus is devel-
oping that the lead isotope clock of the Earth may have been
reset by formation of the Earth's core as late as 4500 million
years ago, which is significantly younger than the age of most
meteorites, now known to be 4560 million years old. If this turns
