Geology Reference
In-Depth Information
Patterson's Age of the Earth isochron.
Patterson showed that ocean-floor samples fell on the same
uranium-lead time line (isochron) defined by the meteorites
(squares). This meant that both the Earth and meteorites must be
4.55 billion years old, and must have formed from the same
cosmic material. If either had started out with di¬erent primeval
lead values they would not now fall on the same line. The dashed
lines show how the lead isotope values have evolved over time
since the 'fixing' of primeval lead in the Universe, as represented
by the Canyon Diablo meteorite.
content of three stony and two iron meteorites and showed how
the values for all five, despite large di¬erences in their long
history, fell on a straight line (isochron) which defined an age
of 4550 million years, give or take 70 million. This proved that
all five meteorites had the same age, but unless values from the
Earth also fell somewhere along that line, a coeval origin would
not be confirmed. But what would be suitable to represent a sin-
gle sample from the Earth, with its hugely diverse rock types?
Patterson had a brilliant idea. He reasoned that because deep-
sea sediments accumulating on the ocean floor must represent
