layla el dating - Isotopic age dating patterson

In spite of those handicaps, Patterson was able to attain processing blanks of circa 0.1 microgram, a very impressive achievement at the time, but now approximately equal to the total amount of sample lead commonly used for isotope analyses. Despite several obvious disadvantages, the method seemed to give reasonable dates on many rocks.His dissertation in 1951 did not report lead analyses from meteorites; instead it gave lead isotopic compositions for minerals separated from a billion-year-old Precambrian granite. Brown saw that the work of Patterson and me would eliminate those problems, so we arranged to study one of Larsen's rocks.Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 95. In exciting progression came discovery of isotopes by J. Thomson in 1912, invention of the mass spectrometer by Dempster (1918) and Aston (1919), the first measurement of the isotopic composition of Pb (Aston, 1927) and the final approach, using Pb-Pb isotopic dating, to the correct age of the Earth: close-2.9 Ga (Gerling, 1942), closer-3.0 Ga (Holmes, 1949) and closest-4.50 Ga (Patterson, Tilton and Inghram, 1953).

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In retrospect it was an extremely unfavorable environment for lead work. Larsen, Jr., who was working on a method for dating zircon in granitic rocks by an alpha-lead method.

None of the modern techniques, such as laminar flow filtered air, sub-boiling distillation of liquid reagents, and Teflon containers were available in those days. Alpha counting was used as a measure of the uranium and thorium content; lead, which was assumed to be entirely radiogenic (produced by the decay of uranium and thorium), was determined by emission spectroscopy.

(I finally also ended up using the mass spectrometer with isotope dilution instead of alpha counting.) In part, our projects would attempt to verify several trace element abundances then prevalent in the meteorite literature which appeared (and turned out to be) erroneous, but Harrison also had the idea that lead isotope data from iron meteorites might reveal the isotopic composition of lead when the solar system first formed.

He reasoned that the uranium concentrations in iron meteorites would probably be negligible compared to lead concentrations, so that the initial lead isotope ratios would be preserved.

We finally obtained lead and uranium data on all of the major, and several of the accessory, minerals from the rock.