Age dating metamorphic rocks

For example, age dates from volcanic rocks that cooled quickly can give an age that is very close to the age of the eruption of the volcanic flow.

Since it takes plutonic rocks millions of years to cool, the age from a mineral that formed in the pluton could be close to the age of intrusion or close to the age of the final crystallization, depending on when it formed in the intrusion.

The calculated age is the age from which the rock or mineral stabilized.

The interpretation of the age date also depends somewhat on the kind of rock being analyzed.

Other decay reactions that are used to calculate absolute age are carbon‐14 to nitrogen‐14, potassium‐40 to argon‐40, rubidium‐87 to strontium‐87, thorium‐232 to lead‐208, and uranium‐235 to lead‐207.

An isotope's half‐life is the time it takes for half of a known quantity of radioactive material to convert to its daughter product.

This radioactive decay begins after the elements are locked into crystalline mineral structures.

Some elements have variations called isotopes, which are atoms that contain different numbers of neutrons in their nuclei.

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Radioactive elements decay at known rates of speed.Absolute age dates have confirmed the basic principles of relative time—for example, a uranium‐lead date from a dike that intrudes into an older rock always yields an absolute age date that is younger than the absolute age date of the enclosing rock.Thousands of comparisons between absolute ages and relative time relationships have proven that radiometric age dating works.As an element decays it creates a series of daughter products.For example, uranium‐238 loses protons and neutrons during its decay, going through a series of intermediate daughter products to form its end product lead‐206, a stable isotope. By determining the relative amounts of a radioactive isotope and its decay products in a mineral, the of the mineral can be determined.

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