Radiometric dating of the oldest rocks on earth dating in un

Posted by / 09-Jul-2017 22:14

Radiometric dating of the oldest rocks on earth

Ideally, the mineral crystals in igneous rocks form a closed system--nothing leaves or enters the crystal once it is formed.This means that as radioactive parent elements decay, they and their daughters are trapped together inside the crystal.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.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.One line of evidence involves rocks from outside the Earth--meteorites and moon rocks.Radiometric dating shows that almost all meteorites are between 4.5 and 4.7 billion years old.

The fourth, lead 204, is not the result of radioactive 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.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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Once scientists have determined the parent-daughter ratio, they can use this measurement along with half-life of the parent to calculate the age of a rock containing the radioactive isotope.