Radioactive dating age of earth
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 nucleus of an atom is made up of protons and neutrons.) For example, the element carbon, which always has six protons in its nucleus, has three isotopes: one with six neutrons in the nucleus, one with seven, and one with eight.
Some isotopes are stable, but some are unstable or radioactive.
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 shows that almost all meteorites are between 4.5 and 4.7 billion years old.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.Over time, radioactive isotopes change into stable isotopes by a process known as radioactive decay.Some radioactive parent isotopes decay almost instantaneously into their stable daughter isotopes; others take billions of years.