Uranium geologic dating with

Lead is a member of Group IVB of the periodic table with two oxidation states (Pb and Pb ), but the chemistry of the element is dominated by Pb ion. Lead has four isotopes with three of them being the tdtimate decay products of uranium and and, therefore, widely used in geological dating. The crystal structure of lead in solid form is face-centered cubic (FCC) with a lattice parameter of 4.95 A at 20°C. Lead is a blue-gray metal with density (11.3 g/cm ) 50 % more than that of steel and four times that of aluminum. However, lead is malleable, soft, and melts at only 327°C, and therefore, readily cut and shaped into pipes and sheets since ancient times. 

SOURCE C. Lewis, The Dating Game (Cambridge Cambridge University Press, 2000) A. Holmes, The Association of Lead with Uranium in Rock-Minerals, and Its Application to the Measurement of Geological Time," Proc. Royal Soc. Lond. A 1911, 85, 248. 

The laws of radioactive decay are the basis of chronology by nuclear methods. From the variation of the number of atoms with time due to radioactive decay, time differences can be calculated rather exactly. This possibility was realized quite soon after the elucidation of the natural decay series of uranium and thorium. Rutherford was the first to stress the possibility of determining the age of uranium minerals from the amount of helium formed by radioactive decay. Dating by nuclear methods is applied with great success in many fields of science, but mainly in archaeology, geology and mineralogy, and various kinds of chronometers are available. 

With its predictable and unchanging rates, radioactive decay has provided scientists with a technique for determining the age of fossils, geological formations, and human artifacts. Using a knowledge of the half-life of a given radioisotope, one can estimate the age of an object in which the iso- tope is found. Four different isotopes are commonly used for dating objects carbon-14, uranium-238, rubidium-87, and potassium-40. Now look at one of these techniques in more detail. 

Holmes A (1911) The association of lead with uranium in rock-minerals and its application to the measurement of geological time. Proc Roy Soc London A 85 248-256 Holmes A (1954) The oldest dated minerals of the Rhodesian Shield. Nature 173 612 Holmes A (1955) Dating the Precambrian of peninsular India and Ceylon. Proc Geol Soc Canada 7 81-106 Holmes A, Cahen L (1955) African geochronology. Col Geol Min Res 5 3-38... 

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