Radioactive dating of rock samples is a method of Free chat with sheamale
This means that zircon data can tell us not only when a rock formed, but also when significant events occurred during its life.The oldest zircon yet found dates from 4.4 billion years ago.The straight line takes the zircons off the concordia. The disturbing event affects the zircons unequally, stripping all the lead from some, only part of it from others and leaving some untouched.The results from these zircons therefore plot along that straight line, establishing what is called a discordia. If a 1500-million-year-old rock is disturbed to create a discordia, then is undisturbed for another billion years, the whole discordia line will migrate along the curve of the concordia, always pointing to the age of the disturbance.His Ph D thesis was on isotope ratios in meteorites, including surface exposure dating.He was employed at Caltech's Division of Geological & Planetary Sciences at the time of writing the first edition.With 238U the Pb/U ratio grows much more slowly with age, but the idea is the same.If you took rocks of all ages and plotted their two Pb/U ratios from their two isotope pairs against each other on a graph, the points would form a beautiful line called a concordia (see the example in the right column).
Some zircons are obviously disturbed and can be ignored, while other cases are harder to judge.
In these cases, the concordia diagram is a valuable tool.