Geoscience Reference
In-Depth Information
hope: 'Hibernium' was named by John Joly in 1922 but was later
discovered to be in fact samarium.
A SELF-GENERATINGHEAT SOURCE: HEATING UP THE
COOLING EARTH
So how did geological research benefit from the discoveries of radio-
active elements? In several ways. By the turn of the twentieth century
the geological community was in turmoil. The evolutionary ideas and
the chronology needed for themwere at variance with the chronology
based on Thomson's cooling Earth model, and the sedimentation
and oceanic salination models produced figures of approximately 100
million years that appeared to be too low for the palaeontologists too.
There was no consensus and geologists were wading through argu-
ments over theories that appeared to have little foundation. Suddenly
radioactivity provided one solution to this problem: heat.
One day early in 1903 Pierre Curie, and his assistant Albert
Laborde, noticed that the radium that he and his wife had so lovingly
isolated appeared to be generating heat. To test this they placed in a
sealed tube, fitted with a thermocouple to record any temperature rise,
one gram of barium chloride contaminated with a small amount of
radium, and into another similar tube placed a gram of pure barium
chloride. Some time later they found that the radium-bearing tube
was 1.5 degrees Centigrade hotter than the comparative tube, and
subsequently they worked out that the heat produced daily by one
gram of radium could melt one gram of ice. Radium was a source of
heat, and they announced this irrefutable fact to the scientific world
on 16 March 1903. In trying to understand the source of the heat Curie
and Laborde suggested that it was either generated during the break-
down of the radium atom, or that it might have been absorbed by
the radium from elsewhere. Joseph John Thomson (1856-1940) (no
relation to Lord Kelvin) in 1903 suggested that the heat might have
been produced as the atom contracted. At much the same time
Ernest Rutherford (Figure
13.1
) and his assistant Frederick Soddy
(1877-1956) discovered that a great deal of energy was produced as
