彼得森几乎马上把注意力转向大气里那个铅的问题。他吃惊地发现，有关铅对人体的影响，人们仅有的一点儿认识几乎无一例外是错误的，或者是令人产生误解的──这也不足为怪，因为40年来对铅的影响的每项研究，全是由铅添加剂的制造商们提供资金的。

　　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.

　　在一项这样的研究中，一名没有受过化学病理学专门训练的医生承担了一个五年计划。根据计划，他让志愿者们吸入或吞下越来越大量的铅，然后对他们的大小便进行化验。不幸的是，那位医生似乎也不懂，铅不会被作为废物排泄出体外，只会积累在骨头和血液里──这正是铅很危险的原因，他既没有检查骨头，也没有化验血液。结果，铅被宣布对健康毫无影响。

　　铅毒

　　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.

　　彼得森很快确认，大气里有过大量的铅──实际上现在仍有大量的铅，因为铅从来没有消失──其中大约90%来自汽车的废气管，但他无法加以证明。他需要一种方法，把现在大气里铅的浓度，与1923年四乙铅开始商业生产之前的浓度进行比较。他突然想到，冰核可能会提供这个答案。

　　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).

　　人们知道，在格陵兰岛这样的地方，每年的积雪层次很分明（因为季节温差使得冬季到夏季的颜色稍有不同）。