Friday, October 19, 2007

We Owe This Man a Lot

Clair Patterson (1922-1995) was a modest geochemist from Iowa. Most people have never heard of him. That's a bit unfortunate given what he has done for us all. He is most often remembered as the man who first determined the age of the Earth to be 4.5 billion years, which stands to this date. That would be enough to put anybody's name in the history books, but Clair Patterson did so much more that has benefited all Americans in a real way.

Patterson received an undergraduate degree in chemistry from Grinnell College and a masters from the University of Iowa (his thesis was in molecular spectroscopy). He then went to the University of Chicago where he worked on the Manhattan Project during World War II. He continued his classified work in Oak Ridge, Tennessee, at the uranium isotope separation plant. After the war he returned to Chicago for his PhD where his research focused on developing methods for measuring isotopic composition and concentrations of lead in igneous rocks as well as meteorites. It was this lengthy period of almost five years, developing the methods for separating and analyzing lead isotopes in microgram and sub-microgram quantities, that allowed him to estimate the Earth's age. He applied these techniques on the Canyon Diablo iron meteorite and in 1953 published the results. By this time, he had moved to California as a Research Fellow at CalTech.

This new ability to isolate microgram quantities of lead from ordinary rocks and sediments opened up new research areas for geochemists. Patterson began collecting data from across the world and this led to a frightening discovery. He compiled the amounts of industrial lead entering the environment from gasoline, solder, paint, and pesticides and showed that they were extremely high. He estimated the concentration in blood for many Americans to be over 100 times that of the natural level. Patterson reported this in his famous 1965 paper titled "Contamination and Natural Lead Environments of Man." [1] He found, from Greenland ice core samples, that atmospheric lead levels increased dramatically soon after tetra-ethyl lead became a common gasoline additive (to prevent engine knock).

Patterson felt so strongly about this subject that he lobbied California and national legislators. While he gained many enemies, especially in the Ethyl Corporation, he also gained many followers. Their efforts led to the enactment of the 1970 Clean Air Act. The U.S. began reducing lead in gasoline around 1973 and it was completely removed in 1987. In 1991, scientists reported that lead in the Greenland snow/ice had fallen by a factor of 7.5 since 1971. By 1993 lead solder was removed from all food containers in the United States, as well as from paints and water lines. And, most important to us, by the late 1990s lead levels within the blood of Americans has reportedly dropped by as much as 80%.

Patterson was elected to the National Academy of Sciences in 1987. In addition to receiving numerous awards for his work, the Vesta family asteroid 2511 was named after him, as was a peak in Antarctica. The international Geochemical Society offers the annual Clair C. Patterson Award for innovative breakthroughs in environmental geochemistry. CalTech interviewed him as part of their Oral Histories project and offers the transcript here.

Here are a few more links for those interested. National Academy of Sciences Biographical Memoirs description of Patterson, his work and his life (cited above as [1]). Berkeley's description of Patterson's work in radiometric dating and dating the Earth.

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