What is chronometric dating
One of its great advantages is that any sample provides two clocks, one based on uranium-235's decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238's decay to lead-206 with a half-life of about 4.5 billion years, providing a built-in crosscheck that allows accurate determination of the age of the sample even if some of the lead has been lost.
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All the samples show loss of lead isotopes, but the intercept of the errorchron (straight line through the sample points) and the concordia (curve) shows the correct age of the rock.
The uranium-lead radiometric dating scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years.
It does not, however, allow one to independently assign an accurate estimation of the age of an object as expressed in years.An error margin of 2–5% has been achieved on younger Mesozoic rocks.Uranium-lead dating is often performed on the mineral zircon (Zr Si O4), though it can be used on other materials, such as baddeleyite.If you're behind a web filter, please make sure that the domains *.and *.are unblocked.This volume of papers delivered to The Royal Society in February of 1992 explores the debate over the "single center" hypothesis of human origins versus "multi-regional evolution." Over the last five years there has been growing support for a recent "Out of Africa" origin of modern humans--based on fresh interpretations of the palaeoanthropological and archaeological evidence, new applications of physical dating techniques to important sites, and a greatly increased genetic data base on recent human variation and its geographical patterning.