Saturday, 31 October 2015

Lead (Part 1): Clair Patterson - Determining an Age of the Earth and his Crusade to Remove Lead in the Environment

Claire Cameron Patterson (1922-1995) was an American geo-chemist who, in 1953 worked out that the Earth is 4.55 billion years (Ba) old, give and take 60 or 70 million years.  This was a remarkable achievement in an environment of ever-changing estimates of the Earth's age ranging from 100 million years to 3.5 billion years.  Patterson's value of 4.55 Ba has stuck and even after 60 years, the age of the earth, in round numbers is still quoted as 4.5 Ba.  Patterson was a pioneer of radiometric geo-chronology; the science that uses radioactive isotopes and their decay products which are present in a rock, to evaluate the date when the rock was formed.  

Arthur Holmes, called the father of modern geochronology, started dating rocks in 1910 using uranium-lead dating methods and perfected many of the procedures in the following 40 years. Holmes is recognized for his perseverance against the well-entrenched feeling of geologists regarding the age of rocks, especially of a much younger Earth. 
In fact, there was really no method available for determining an absolute geological timescale and everybody worked with relative ages of different types of rocks based on fossil records - a highly unsatisfactory situation. One could say that it was Holmes' mission and ambition to find an absolute geological time scale and do away with the uncertainties in interpreting data relating to the age of rocks, sediments, fossils - in effect set out a time scale against which dynamics of our planet's evolution could be understood.
It might be fair to say that by measuring absolute ages, Arthur Holmes's work elevated geology to a 'Science' capable of making quantitative analysis  and predictions that could be empirically confirmed.  His work also provided a time scale for life sciences against which Darwin's evolution could be understood.

During WWII, Patterson worked on the Manhattan Project and was based in Oak Ridge.  The work in Oak Ridge concerned with the enrichment of uranium-235 for the atomic bomb and the experience with mass spectrometers was invaluable for Patterson to develop the radioisotope dating methods.  Lead (Pb) is the stable end product in the decay of uranium (U).  Uranium is radioactive and the two relevant isotopes of U have masses 238 and 235 decaying with half-lives (time for half of a sample of the radioactive isotope to decay) of 4.48 and 0.7 Ba respectively, resulting in end products of Pb isotopes of masses 206 and 207.  Essentially, for determining the age of a rock or a meteorite, one is required to measure minute quantities, of the order of pico-grams (a billionth of a milligram) of U and nano-grams (a millionth of a milligram) of Pb isotopes.  Patterson developed methods to measure such minute quantity of lead present in his samples. 

 In addition to the ages of Earth, Moon, and meteorites,
radiometric dating has been used to determine ages of fossils, timing of glaciations, ages of mineral deposits, recurrence rates of earthquakes and volcanic eruptions, the history of reversals of Earth's magnetic field, and the age and duration of a wide variety of other geological events and processes.

George Tilton in the biographical account describes Patterson's next big project to measure the isotopes of lead in ocean sediments with a view to obtain information about the ages and compositions of the landmasses draining into the oceans.  In 1962, Patterson showed that the ocean surface water contained up to 10 times more lead than deep ocean water. Other metals like barium did not show this trend.  
He showed further that blood lead levels in Americans was over 100 times the prehistoric levels and attributed this to the vast quantities of lead entering the environment from sources like paint, petrol, solder and water pipes.  It seemed that the population en mass was being poisoned by the prevailing industrial activity.

The lead contamination problem was so pervasive that even the blanks, used as standards, were contaminated with lead and the measured lead levels were grossly under-estimated.  

The response from big business was as expected. They did everything in their powers to discredit and isolate Patterson.  Patterson's results were called 'rabble rousing'. Even the regulatory bodies did not believe what Patterson was trying to tell them which in his view required immediate action.  It took Patterson almost two decades to have his views totally accepted by the Environmental Protection Agencies with a significant improvement in the health of the people throughout the world.

In Part II, I shall look at lead as an environmental poison and its effects on the human body.  In Part III, I shall discuss the inadequacy of our regulatory systems and put the lead poisoning episode in relation to many other failings in the way our system works.

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