Geology Reference
In-Depth Information
contain the specific characteristics of helium. Generously,
Rutherford lent Soddy and Ramsay his piece of radium bromide
so that they could confirm the experiment.
Remarkably, it seemed, as radium decayed not one but two
gases were being produced - radon and helium. But there was
more! Soddy soon realised that radon too was unstable and
when it decayed, it also produced helium, and was also trans-
formed to yet another new element. The miracle was getting
wilder and wilder.
Ultimately they established that in the 'decay chain' that started
with an unstable 'parent' atom of uranium, a 'daughter' atom
of radium was produced and helium liberated; in turn that
unstable radium atom decayed to its 'daughter' product radon,
also creating helium in the process, and so on through fourteen
stages until eventually eight atoms of helium had been dis-
charged and a completely new stable element was formed that
had started life, a very long time ago, as an atom of uranium.
But where did the decay chain stop? What was that stable new
element? Well, it was to be almost another decade before Arthur
Holmes confirmed that, but in the meantime the coffin lid was
slowly closing on Kelvin's twenty million years.
The final event in this particular wild voyage of discovery was
made by Pierre Curie at the same time as Soddy was working on
helium, and a couple of months before he and Marie were
awarded their Nobel Prize in 1903. With his young assistant
Albert Laborde, Pierre detected that the radium he and Marie
had isolated was constantly releasing heat. As electrons were
explosively emitted from the atom, energy was being given out
in the form of heat: 'Every hour radium generates enough heat
to melt its own weight in ice' they announced. Here at last was
the evidence geologists had been waiting for. While Kelvin
might still be right in that the Earth could have been cooling
down from a time when it had been a molten globe, what he
had not known was that at the same time as the Earth was cool-
ing, radioactive elements within the Earth were generating
