Any contamination of a sample by outside carbon (even from the researcher's fingerprints) had to be fanatically excluded, of course, but that was only the beginning.
Delicate operations were needed to extract a microscopic sample and process it.
De Vries thought the variation might be explained by something connected with climate, such as episodes of turnover of ocean waters.(7) Another possible explanation was that, contrary to what everyone assumed, carbon-14 was not created in the atmosphere at a uniform rate.
Some speculated that such irregularities might be caused by variations in the Earth's magnetic field.
Making the job harder still, baffling anomalies turned up.
The carbon-14 dates published by different researchers could not be reconciled, leading to confusion and prolonged controversy.
The prodigious mobilization of science that produced nuclear weapons was so far-reaching that it revolutionized even the study of ancient climates.
But what looks like unwelcome noise to one specialist may contain information for another.
In 1958, Hessel de Vries in the Netherlands showed there were systematic anomalies in the carbon-14 dates of tree rings.
His explanation was that the concentration of carbon-14 in the atmosphere had varied over time (by up to one percent).
One application was a timetable of climate changes for tens of thousands of years back.
Many of the traditional chronologies turned out to be far less accurate than scientists had believed a bitter blow for some who had devoted decades of their lives to the work.