Geoscience Reference
In-Depth Information
honor had included George Darwin, Davy, Faraday, Lyell, Maxwell, Tyndall, and
many other notables.
The audience of nearly eight hundred included the cream of British science, as-
sembled to hear Rutherford report the results of his experiments on radioactivity.
Few in the audience could have fully understood the brave new world of transmut-
ing atoms that Rutherford described. To some, his science may have seemed closer
to alchemy. Lord Kelvin was in the audience, as Rutherford was said often to re-
count:
I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience
and realized that I was in trouble at the last part of my speech dealing with the age of the earth,
where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the
important point, I saw the old bird sit up, open an eye and cock a baleful glance at me! Then a
sudden inspiration came, and I said Lord Kelvin had limited the age of the earth, provided no
new source was discovered. That prophetic utterance refers to what we are considering tonight,
radium! Behold, the old boy beamed upon me.
5
The discovery of radioactivity both falsified Kelvin's calculations for the age of
the Sun and provided the means of making a correct calculation of the age of the
Earth. “The discovery of the radio-active elements, which in their disintegration
liberate enormous amounts of energy, thus increases the possible limit of the dur-
ation of life on this planet,” Rutherford said, “and allows the time claimed by the
geologist and biologist for the process of evolution.”
6
Others, including George Darwin and John Joly, had noted before Rutherford's
lecture that if radium were present in the Sun, “the supply of solar heat must no
longer be regarded as affording a major limit both to solar age and geological
Perry had all recognized: one or more of Kelvin's assumptions could as well be
false as true.
The discovery of radioactivity reversed the downward trend in estimates of the
Earth'sage, prompting Joly to write that “the hundred million years which the doc-
trine of uniformity requires may, in fact, yet be gladly accepted by the physicist.”
8
Uniformitarianism did not require one hundred million years—that was Joly's salt
clock. But the physicists soon showed that they would not be glad to accept 100
million years, nor even 1,000 million.
In his cautions about “operations . . . which are impossible under the laws to
which the known operations going on at present in the material world are subject”
and “sources now unknown to us . . . prepared in the great storehouse of creation,”
Kelvin had seemed to anticipate radioactivity. But after its discovery, he never ac-
knowledged that the existence of radioactive heat required him to change his as-
