Geology Reference
In-Depth Information
In the end the specimens used by Holmes
'were detached
from a small collection which belongs to the Geological
Museum of the Imperial College'
.
Meteorites fall into two main categories - iron and stony -
which are further divided into classes. Holmes argued that
'for
each type of meteorite there corresponds a terrestrial zone
[on
Earth]
'
and set out to illustrate this by making some exquisitely
delicate analyses of the tiny amounts of radium in meteorites.
Making the assumption that iron meteorites represented part of
the core of a once much larger body with a stony exterior, in the
same way that the Earth has an iron core with a stony exterior,
he compared radium values obtained on meteorites with those
from rocks on Earth, and showed that in both cases the amount
of radium decreased towards the core. Furthermore, the radium
values in the stony meteorites were found to be very similar to
those found in rocks known to come from deep within the Earth,
and because no radium was seen in the iron meteorites he
inferred that none would be found in the Earth's iron core.
A genetic link between the Earth and meteorites was clearly
indicated by this radium study, and the tremendous significance
of this work was not lost on Holmes. He concluded:
'The prob-
lems that are suggested by . . . this inquiry are of supreme
geological importance. The evolution of the Earth, of its zonal
structure, and particularly of its crust are all questions which
remain to be solved.'
Indeed, most of those questions are still
being addressed today even though Holmes was to devote a
great deal of time to them over the following years, profoundly
contributing to our understanding of the Earth and the evolution
of its crust.
But the amount of meteoritic material available to Holmes at
that time was small, and in 1914 he was again writing to the
British Museum:
'I have been working on the radium content
of meteorites and . . . am applying this to the meteoric analogy
of the Earth's internal constitution . . . I have now used up
the few meteorites which were in my possession, but I am
