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to separate and analyze. But Patterson soon discovered that industrial lead is so
pervasive in the environment, and the effects of its contamination so difficult to
remove, that almost all previously reported lead abundances in meteorites reflec-
ted the amount of contaminant lead rather than the amount inherent in the meteor-
ites themselves. The discovery of the extent of environmental lead pollution would
eventually change Patterson's career path, to our everlasting benefit.
The modern figure for the age of the Earth derives from Claire Patterson's
classic 1956 paper “Age of Meteorites and the Earth.” 10 There he reported the
lead-isotope ratios from three stone meteorites, which contain appreciable uranium
and therefore have evolved a radiogenic lead component, and two uranium-free
iron meteorites, one of them the so-named Canyon Diablo meteorite from Meteor
Crater, Arizona, which we will meet in part 3 . Having no uranium, these two had
preserved their primordial lead ratios. For the group, Patterson calculated an age of
4.55 ± 0.07 billion years. This, he argued, was the age of the meteorites, the Earth,
and the solar system.
Patterson's life and career serve as a model of the transition that many scientists
have found themselves making. At first devoting himself to purely scientific ques-
tions, Patterson's attention inevitably turned to the implications of environmental
lead for human health. Rather than play this up, Patterson preferred the role of the
no-nonsense scientist whose goals, as he put it, were nothing but “science, science,
science.” 11
Patterson's environmental awareness began with his need to identify the source
of the ubiquitous environmental lead. He soon discovered high concentrations of
lead in the surface waters of the ocean and in otherwise pristine snow. Lead in
snow could only have come from the atmosphere, and it could only have gotten
there from leaded gasoline. To prove this point, Patterson participated in one of
the most arduous experiments in modern science. He measured the amount of lead
in hard-won ice cores from Greenland, finding that the amount of lead in the at-
mosphere had risen slowly from the beginning of the Industrial Revolution until
the 1920s, when gasoline manufacturers began to add lead to their product. At that
point, the level of lead in the atmosphere shot up. It continued to climb until by the
1970s it had reached two hundred times the natural level. Humans were polluting
the atmosphere with a poisonous substance: lead.
Patterson fought for years to get his findings into the public arena. The leaded
gasoline industry responded with the same deceptive and dishonest techniques that
Big Tobacco and Big Oil would later use to sow doubt about the dangers of their
products. But Patterson's impeccable science overcame their smoke and mirrors.
His research was key to the passage of the Clean Air Act of 1970. In 1995, Patter-
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