Geology Reference
In-Depth Information
I hope when you get going again
[after the war]
you will try
to clear up the extraordinary discrepancies in the Manitoba
results. I feel sure that the true age must be of the order of
2000 m.y. or more, and this is of the greatest interest, not
only because the rocks here seem to be the oldest yet found,
but also because such a figure shows that current views about
the expanding universe need revision - not perhaps to be won-
dered at!
.
Indeed, while astronomers may have been prepared to stretch
a point and agree with the geologists that 'within error' the age
of the Earth and the Universe were more or less the same at
2000 million years, Holmes did not feel constrained by the
astronomers to do likewise. If the age of the Manitoba pegmatite
meant that the age of the Earth became at least 500 million years
older than the Universe, then it must be the astronomers who
had got it wrong. For what was evident to Holmes as a geolo-
gist but not to the astronomers nor to Nier as a physicist, was
that the Manitoba pegmatite was the
youngest
rock in a much
older sequence.
Geological investigations had shown that the sequence had
started to accumulate in a primordial ocean when a huge thick-
ness of sediments, some several kilometres deep, was deposited
on the ocean floor as an ancient continent was being eroded
away. These sediments had been buried to great depths where
they became very hot, partially molten, and metamorphosed into
a gneiss. Uplifted during a period of mountain building, the
gneiss was then intruded by multiple phases of molten lavas
until finally the residual fluids and gases, now highly concen-
trated in elements such as uranium and lead, crystallised out to
form the Manitoba pegmatite. Holmes realised that the whole
process from deposition on the ocean floor to final formation
of the pegmatite must have taken many hundreds of millions
of years, so if the pegmatite itself was giving an age around
2500 million years, then the gneiss it intruded, which had once
been ocean floor sediments, may well be 3000 million years old.
