Here are some quotations from Darwin's Ghost" by Steve Jones (page 195).
Some chemicals are useful for dating the past. Potassium has half-life of rather more than a billion years as it breaks down to argon.
Carbon-14 -- a radioactive form of the atom upon which life is based -- has in contrast, a half life of a mere five thousand, seven hundred and thirty years.
The book, Darwin's Ghost is a modern update to Darwin's "Origin," using identical chapter names found in Darwin's work. It is a fascinating and fabulous read.
Well obviously they did not use Carbon14 dating if they arrived at such an old age. But I was wondering if somebody here knew how they did in fact measure it, and I am not sure that asking the ghost of Darwin would be a terribly useful way to seek the answer.