His main work done, Patterson now turned his attention to the nagging question of all that lead in the atmosphere. He was astounded to find that what little was known about the effects of lead on humans was almost invariably wrong or misleading—and not surprisingly, he discovered, since for forty years every study of lead's effects had been funded exclusively by manufacturers of lead additives.
In one such study, a doctor who had no specialized training in chemical pathology undertook a five-year program in which volunteers were asked to breathe in or swallow lead in elevated quantities. Then their urine and feces were tested. Unfortunately, as the doctor appears not to have known, lead is not excreted as a waste product. Rather, it accumulates in the bones and blood—that's what makes it so dangerous—and neither bone nor blood was tested. In consequence, lead was given a clean bill of health.
Patterson quickly established that we had a lot of lead in the atmosphere—still do, in fact, since lead never goes away—and that about 90 percent of it appeared to come from automobile exhaust pipes, but he couldn't prove it. What he needed was a way to compare lead levels in the atmosphere now with the levels that existed before 1923, when tetraethyl lead was introduced. It occurred to him that ice cores could provide the answer.
It was known that snowfall in places like Greenland accumulates into discrete annual layers (because seasonal temperature differences produce slight changes in coloration from winter to summer).