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years for the age of the earth. Only the evolutionists found this number im-
plausible, for they believed that the workings of organic evolution required
much longer stretches of time to generate all the organic diversity found on
earth today. As we know now, their misgivings were well founded. The ttue
age of the earth is measured in billions of years, not millions. This discovery
came about as a by-product of developments in the field of nuclear physics,
which eventually gave us a means of dating volcanic ash.
Near the close of the nineteenth century, at the peak of Kelvin's emi-
nence, the seeds of his downfall—in terms of his estimate of the earth's
age—had just been sown. In 1895 Wilhem Roentgen of German discovered
X-rays, and a year later A. Becquerel of France discovered the radioactive
properties of uranium. Two years after that, Marie Curie discovered similar
properties for the element thorium and coined the word
radioactivity.
Radioactive decay
The breakthrough leading from the first discovery of X-rays and radioactive
elements to accurate age determination in geology came from Ernest Ruther-
ford and Frederick Soddy of McGill University in Montreal, who discovered
the principle of radioactive decay and "half-life." In radioactive decay, an
atomic nucleus undergoes transformation into one or more different nuclei,
the original element often becoming in the process a different element. By
1907 Rutherford made the first suggestion that radioactive decay processes
could be used as a geological timekeeper:
If the rate of production of helium from known weights of the dif-
ferent radio-elements were experimentally known, it would thus
be possible to determine the interval required for the production
of the amount of helium observed in radioactive minerals, or, in
other words, to determine the age of the mineral.
These prophetic words heralded a new era of age determination.
Rutherford quickly calculated the age of two minerals, finding
minimal
ages
