Dating of the earth

Radiometric dating works best on igneous rocks, which are formed from the cooling of molten rock, or magma.

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.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 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.

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