Radioactive dating rates
The third, which by the end was the most acute, presented a problem that outlasted the controversy itself.Thus, when in 1919 Shapley stated that for him the radiometric timescale was fully established, he acknowledged that there was as yet no explanation for the sun’s energy. In 1920 Sir Arthur Eddington came up with the answer: the fusion of hydrogen into helium.) In reply to Lord Kelvin’s attacks, the geologists used two principal lines of reasoning.
Radioactivity offered not only a resolution to the puzzle of the earth’s energy supply but also a chronology independent of questionable geologic assumptions and a depth of time more than adequate for the processes of evolution.Lord Kelvin and his allies used three kinds of argument.The first of these referred to the rate of heat loss from the earth and the length of time it would have taken to form its solid crust.The first argument was completely undermined after taking into account the amount of heat generated by radioactive decay.The second depended on highly dubious theories of formation of the earth and moon and plays relatively little role in this compilation. Roman poet Lucretius, intellectual heir to the Greek atomists, believed its formation must have been relatively recent, given that there were no records going back beyond the Trojan War.
The Talmudic rabbis, Martin Luther and others used the biblical account to extrapolate back from known history and came up with rather similar estimates for when the earth came into being.
It is a drama consisting of a prologue and three acts, complex characters, and no clear heroes or villains.
We, of course, know the final outcome, but we should not let that influence our appreciation of the story as it unfolds.
Even less should we let that knowledge influence our judgment of the players, acting as they did in their own time, constrained by the concepts and data then available.
One outstanding feature of this drama is the role played by those who themselves were not, or not exclusively, geologists.
This position came to be known as uniformitarianism, but within it we must distinguish between uniformity of natural law (which nearly all of us would accept) and the increasingly questionable assumptions of uniformity of process, uniformity of rate and uniformity of outcome.