Radioactive dating metamorphic rocks

Radiometric dating, or radioactive dating as it is sometimes called, is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes.

Different methods of radiometric dating can be used to estimate the age of a variety of natural and even man-made materials.

With this in mind geologist have long known that the deeper a sedimentary rock layer is the older it is, but how old?

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Using this process geologists are able to assign actual ages with known degrees of error to specific geologic events.

By combining knowledge gained using both relative and absolute dating processes geologists have been able to produce the geologic time scale.

Relative time places events or formations in order based on their position within the rock record relative to one another using six principles of relative dating.

Relative time can not determine the actual year a material was deposited or how long deposition lasted; it simply tell us which events came first.

However, rocks and other objects in nature do not give off such obvious clues about how long they have been around.

So, we rely on radiometric dating to calculate their ages.

For example, uranium-lead dating can be used to find the age of a uranium-containing mineral.

It works because we know the fixed radioactive decay rates of uranium-238, which decays to lead-206, and for uranium-235, which decays to lead-207.

These two uranium isotopes decay at different rates. The half-life of the uranium-238 to lead-206 is 4.47 billion years.

The uranium-235 to lead-207 decay series is marked by a half-life of 704 million years.

This means that a quartz sandstone deposited 500 million years ago will look very similar to a quartz sandstone deposited 50 years ago.

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