Mineral found in granite radiometric dating

Radiometric dating is based on the decay of long-lived radioactive isotopes that occur naturally in rocks and minerals.

These parent isotopes decay to stable daughter isotopes at rates that can be measured experimentally and are effectively constant over time regardless of physical or chemical conditions.

mineral found in granite radiometric dating-87

The main point is that the ages of rock formations are rarely based on a single, isolated age measurement.

On the contrary, radiometric ages are verified whenever possible and practical, and are evaluated by considering other relevant data.

There are a number of long-lived radioactive isotopes used in radiometric dating, and a variety of ways they are used to determine the ages of rocks, minerals, and organic materials.

Some of the isotopic parents, end-product daughters, and half-lives involved are listed in Table 1.

James Hutton, a physician-farmer and one of the founders of the science of geology, wrote in 1788, “The result, therefore, of our present inquiry is, that we find no vestige of a beginning, — no prospect of an end.” Although this may now sound like an overstatement, it nicely expresses the tremendous intellectual leap required when geologic time was finally and forever severed from the artificial limits imposed by the length of the human lifetime.

By the mid- to late 1800s, geologists, physicists, and chemists were searching for ways to quantify the age of the Earth.

Lord Kelvin and Clarence King calculated the length of time required for the Earth to cool from a white-hot liquid state; they eventually settled on 24 million years.

James Joly calculated that the Earth’s age was 89 million years on the basis of the time required for salt to accumulate in the oceans.

The point is that not all methods are applicable to all rocks of all ages.

One of the primary functions of the dating specialist (sometimes called a geochronologist) is to select the applicable method for the particular problem to be solved, and to design the experiment in such a way that there will be checks on the reliability of the results.

For example, a method based on a parent isotope with a very long half-life, such as C method can only be used to determine the ages of certain types of young organic material and is useless on old granites.

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