Geoscience Reference
In-Depth Information
Lead Is the Final Product of Uranium
To Kelvin and Rutherford, the age of the Earth and its constituent rocks and miner-
als were of secondary interest. Kelvin was intent on correcting the great mistake of
British popular geology—belief in Lyellian uniformitarianism—and the age of the
Earth and the Sun provided the means. He had enough other interests practical and
theoretical to occupy several ordinary careers: thermodynamics; laying a cable un-
der the Atlantic Ocean; writing a textbook with Tait; and inventions that included
an improved compass, a machine to sound the depth of the ocean, and one to pre-
dict the tides.
Rutherford wanted to use radioactivity to explore the atom. Once he and his col-
leagues had revealed the basic principles of radioactivity and provided a few ex-
amples of its utility, he moved on to what some might call his greatest scientific
accomplishment: the Rutherford model ofthe atom, with its central nucleus ofpro-
tons and neutrons surrounded by shells of electrons. Niels Bohr, his distinguished
Danish collaborator, said that “Rutherford's achievements are so great that they
provide the background of almost every word that is spoken at a gathering of phys-
1914 he was knighted as Baron Rutherford of Nelson, for his hometown on the
South Island. His list of honors fills two pages.
2
One of the first to stand on Rutherford's broad shoulders was Robert Strutt
(1842-1919), the fourth Baron Rayleigh and a professor of physics at Imperial
College in London. Like Rutherford, Strutt had studied physics under J. J. Thom-
son at the Cavendish Laboratory. He subsequently wrote the biography of this
“other Thomson,” who in 1906 won the Nobel Prize for his discovery of the elec-
tron.
Strutt was elected into the Royal Society in 1905 at age thirty. His citation in-
cluded thirteen scientific papers, each written before he took up the topic that by
itself would have ensured his place in scientific history: pioneering the uranium-
helium method of calculating geologic ages.
From 1908 to 1910, Strutt measured the amounts of uranium and helium in
phosphatic bones, which can have fifty times as much uranium as does the average
rock. Though he found ages as great as 141 million years, they failed to correlate
