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Radiometric dating the age of the earth

At any moment, the ratio between them is a measure of the time elapsed, as long as the system remains closed.But if the hourglass were to break (become an open system), sand leaks out and the hourglass is no longer a reliable tool for telling time.

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Therefore, scientists perform radiometric dating only on rocks or minerals that have remained closed systems.Scientists determined the Earth's age using a technique called radiometric dating.Radiometric dating is based upon the fact that some forms of chemical elements are radioactive, which was discovered in 1896 by Henri Becquerel and his assistants, Marie and Pierre Curie.After one half-life, 50 percent of the original parents remains; after two, only 25 percent remains, and so on.Decay curve of a radioactive element with a half-life equal to one time unit.Radiometric dating works best on igneous rocks, which are formed from the cooling of molten rock, or magma.

As magma cools, radioactive parent isotopes are separated from previously formed daughter isotopes by the crystallization process.

The rates of decay of various radioactive isotopes have been accurately measured in the laboratory and have been shown to be constant, even in extreme temperatures and pressures.

These rates are usually expressed as the isotope's half-life--that is, the time it takes for one-half of the parent isotopes to decay.

The discovery gave scientists a tool for dating rocks that contain radioactive elements.

Many elements have naturally occurring isotopes, varieties of the element that have different numbers of neutrons in the nucleus.

Ideally, the mineral crystals in igneous rocks form a closed system--nothing leaves or enters the crystal once it is formed.