Clair Cameron Patterson

Clair Cameron Patterson
File:Portrait of Clair Cameron Patterson.jpg Clair Cameron Patterson
Born	June 2, 1922 Mitchellville, Iowa, U.S.
Died	Sea Ranch, California, U.S.
Nationality	United States
Fields	geochemistry
Institutions	California Institute of Technology
Alma mater	Grinnell College University of Chicago
Thesis	The Isotopic Composition of Trace Quantities of Lead and Calcium (1951)
Doctoral advisor	Harrison Brown
Known for	uranium-lead dating, age of the Earth, lead contamination
Notable awards	Tyler Prize (1995) V. M. Goldschmidt Award (1980) J. Lawrence Smith Medal (1973)

Clair Cameron Patterson (June 2, 1922 – December 5, 1995) was an American geochemist. Born in Mitchellville, Iowa, United States he graduated from Grinnell College. He later received his Ph.D. from the University of Chicago, and spent his entire professional career at the California Institute of Technology.

In collaboration with George Tilton, Patterson developed the uranium-lead dating method into lead-lead dating, and by using lead isotopic data from the Canyon Diablo meteorite, he calculated an age for the Earth of 4.55 billion years; a figure far more accurate than those that existed at the time and one that has remained largely unchanged since 1956.

Patterson had first encountered lead contamination in the late 1940s as a graduate student at the University of Chicago. His work on this led to a total re-evaluation of the growth in industrial lead concentrations in the atmosphere and the human body, and his subsequent campaigning was seminal in the banning of tetraethyllead in gasoline, and lead solder in food cans.

Early life

Clair (Pat) Patterson was born in Mitchellville, Iowa and graduated from Grinnell College in chemistry where he met his wife to be, Lorna (Laurie) McCleary. They both moved to the University of Iowa for graduate work where he did an M.A. in molecular spectroscopy. Both were then sent to work on the Manhattan Project, first at the University of Chicago and then at Oak Ridge, Tennessee where he encountered mass spectrometry.

After the war they returned to Chicago where Laurie took a research job as an infrared spectroscopist to support Pat whilst he did a Ph.D. at the University of Chicago under Harrison Brown. After a postdoctoral year at Chicago, Patterson moved with Brown to the Division of Geology (later the Division of Geological and Planetary Sciences) at the California Institute of Technology (Caltech) in 1952 as founding members of its geochemistry program. Pat remained at Caltech for the rest of his life. He and Laurie had four children.

Estimate of the Earth's age

Harrison Brown of the University of Chicago developed a new method for counting lead isotopes in igneous rocks, and assigned it to Patterson as a dissertation project in 1948. During this period Patterson operated under the assumption that meteorites are left-over materials from the formation of the Solar System, and thus by measuring the age of one of these rocks the age of the Earth would be revealed. Gathering the materials required time, and in 1953, Patterson had his final specimens from the Canyon Diablo meteorite. He took them to the Argonne National Laboratory, where he was granted time on a late model mass spectrometer.

In a meeting in Wisconsin soon afterward, Patterson revealed the results of his study. The definitive age of the Earth is 4.550 billion years (give or take 70 million years). The current estimate for the age of the earth is 4.54 ± 0.05 billion years (4.54 × 10⁹ years ± 1%).

Tracing the geochemical evolution of the Earth

His ability to isolate microgram quantities of lead from ordinary rocks and determine their isotope composition led him to examining the lead in ocean sediment samples from the Atlantic and Pacific. Deriving from the different ages at which the landmasses had drained into the ocean, he was able to show that the amount of anthropogenic lead presently dispersed into the environment was about eighty times the amount being deposited in the ocean sediments: the geochemical cycle for lead appeared to be badly out of balance.

The limitations of the analytic procedures led to him using other approaches. He found that deep ocean water contained 3-10 times less lead than surface water, in contrast to similar metals such as barium. This led him to doubt the commonly held view that lead concentrations had only grown by a factor of two over naturally occurring levels.

Patterson returned to the problem of his initial experiment and the contamination he had found in the blanks used for sampling. He determined through ice-core samples from Greenland that atmospheric lead levels had begun to increase steadily and dangerously soon after tetraethyllead began to see widespread use in fuel, when it was discovered to reduce engine knock in internal combustion engines. Patterson subsequently identified this, along with the various other uses of lead in manufacturing, as the cause of the contamination of his samples, and because of the significant public-health implications of his findings, he devoted the rest of his life to removing as much introduced lead from the environment as possible.

Campaign against lead poisoning

Main article: Lead poisoning

Beginning in 1965, with the publication of Contaminated and Natural Lead Environments of Man, Patterson tried to draw public attention to the problem of increased lead levels in the environment and the food chain due to lead from industrial sources. Perhaps partly because he was criticizing the experimental methods of other scientists, he encountered strong opposition from recognized experts such as Robert A. Kehoe.

In his effort to ensure that lead was removed from gasoline (petrol), Patterson fought against the lobbying power of the Ethyl Corporation (which employed Kehoe), against the legacy of Thomas Midgley — which included tetraethyllead and chlorofluorocarbons — and against the lead additive industry as a whole. Following Patterson's criticism of the lead industry, he was refused contracts with many research organizations, including the supposedly neutral United States Public Health Service. In 1971 he was excluded from a National Research Council (NRC) panel on atmospheric lead contamination, even though he was the foremost expert on the subject at that time.

The United States mandated the use of unleaded gasoline to protect catalytic converters in all new cars starting with the 1975 model year, but Patterson's efforts accelerated the phaseout of lead from all standard, consumer, automotive gasoline in the United States by 1986. Lead levels within the blood of Americans are reported to have dropped by up to 80% by the late 1990s.

He then turned his attention to lead in food where similar experimental deficiencies had masked the increase. In one study he showed an increase in lead levels from 0.3 to 1400 nanograms per gram in certain canned fish compared with fresh, whilst the official laboratory had reported an increase of 400 ng/g to 700 ng/g. He compared the lead, barium and calcium levels in 1600-year-old Peruvian skeletons and showed a 700- to 1200-fold increase in lead levels in modern human bones with no comparable changes in the barium and calcium levels.

In 1978 he was appointed to a NRC panel which accepted many of the increases and the need for reductions – but, argued the need for more research. His opinions were expressed in a 78-page minority report which argued that control measures should start immediately; including gasoline, food containers, paint, glazes and water distribution systems. Thirty years later, most of these have been accepted and implemented in the United States and many other parts of the world.

Death

Patterson died in his home in Sea Ranch, California at the age of 73 on December 5, 1995. The reported cause of his death was a severe asthma attack.

Further reading

• Denworth, L. Toxic Truth: A Scientist, A Doctor, and the Battle over Lead, Beacon Press, 2009.

External links

• Clair Cameron Patterson — Biographical Memoirs of the National Academy of Sciences