Radioactive dating meteorite

By experimentation, scientists have determined which rocks are suitable for various dating techniques.For K-Ar, for example, igneous rocks are good candidates for testing because they formed directly from molten magma and have a simple history.

At any rate, scientists have devoted a great deal of effort to determining exactly which dating methods are appropriate for which types of rocks.

The other problem to avoid when dating rocks is the possibility that changes to the rock have caused loss or gain of either the parent or daughter element - this would lead to a false date (too old if parent element were lost, too young if daughter element were lost).

I know of two methods that have been designed that can account for this possibility - isochron dating and the uranium-thorium-lead discordia / concordia method (actually three independent age calculations for one sample).

Scientists have settled on the age of the earth of about 4.6 billion years as a result of research started almost 50 years ago.

This conclusion was based upon carefully designed and conducted experiments that compared the ratios in rock samples of parent elements to daughter elements ( some of which would have been from radioactive decay of the parent, some of which may have been present in the sample at the time of formation).

Since radioactive decay is known to occur at a constant rate, the age of a rock can be determined from the ratio of the parent element to the daughter element.

The concerns about these dating methods were exactly the same that creationists continue to raise - presence of the daughter element at the time the rock was formed and possible loss / gain of either the parent or daughter element at some point in the history of the rock.

For this reason, the tests were designed to account for those possibilities.

Initial daughter element can often be accounted for by either measuring the amount of an isotope of the daughter element (the ratio of isotopes are almost always constant).

Another possibility is (as in the case of the potassium - argon - K-Ar method) that because the daughter element is gaseous, it would escape from the rock when the rock was molten.

Once the rock cooled, the gaseous daughter would be trapped in the rocks crystal structure and could no longer escape.

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