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Uranium lead dating method

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This model, which describes the accumulation of lead isotopes in meteorites, the Earth, and the Solar System, was proposed independently by E. The amount of 204Pb will remain constant throughout the history of a rock because it is a stable isotope that is not the product of any decay series, thus allowing for the normalization (Dalrymple 201-163).

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This is because Pb, causing the isochron to decrease in slope with increasing age.The first is that it requires single-stage leads, which are systems that begin at some initial lead composition and remain on the same growth curve throughout their histories (Dalrymple 209).The second requirement is that assumptions about the genetic relationship between the Earth and meteorites must be made.The results from Heaman's team show that the sauropod in question was alive 64.8 million years ago, 700,000 years after the mass extinction, bringing into question the fate of the dinosaurs after the KT extinction.There could be several reasons why the New Mexico dinosaur and its ancestors survived the KT extinction.Second, using two isotopes of the same element makes the sample immune to chemical fractionation during a post-crystallization disturbance (Dalrymple 208). This model ultimately led to the development of isochrons, in which two isotopes are plotted against each other to calculate an age for the mineral or rock.

The commonly accepted 4.5 billion year age of the earth is derived from radiometric dating of lunar rocks and meteorites in addition to dating methods based on the Gerling-Holmes-Houtermans model. Those who developed the method utilized Pb, lead isotopes that are the product of radioactive decay, normalized to 204Pb.

Two other characteristics of lead isotope measurements make it superior to other methods.

First, measuring the isotope ratio of a single element can be done much more precisely than measuring isotope ratios of two differing elements.

The resulting line drawn through the plotted points will pass through a point representing the initial lead composition of the system.

Although this point cannot be determined, the isochron will rotate about it as the rock ages because the initial amount of lead is constant regardless of age.

The use of lead isotope ratios makes this isochron self-checking.