Radioactive atoms decay, or lose energy and subatomic particles…A radioactive isotope is a chemical element that has an unstable nucleus subject to decay.Typically, Carbon 14 is used for fossil dating for fossils 100-30,000 years old, but older than that, Potassium 40 or Rubidium 87 are more effective.

All rocks and minerals contain long-lived radioactive elements that were incorporated into Earth when the Solar System formed.

These radioactive elements constitute independent clocks that allow geologists to determine the age of the rocks in which they occur.

The number of parent atoms originally present is simply the number present now plus the number of daughter atoms formed by the decay, both of which are quantities that can be measured.

Samples for dating are selected carefully to avoid those that are altered, contaminated, or disturbed by later heating or chemical events.

In addition to the ages of Earth, Moon, and meteorites, radiometric dating has been used to determine ages of fossils, including early man, timing of glaciations, ages of mineral deposits, recurrence rates of earthquakes and volcanic eruptions, the history of reversals of Earth's magnetic field, and the age and duration of a wide variety of other geological events and processes.

The above equation makes use of information on the composition of parent and daughter isotopes at the time the material being tested cooled below its closure temperature.The type of radiometric dating used depends greatly on the approximate time period you are studying and so varies depending on if the material you are studying is an artifact or a fossil. Radioactive isotopes in medicine are used to help diagnose certain disease states and isolate regions in the body. In carbon dating, the approximate time taken by the item to degrade to half is calculated according to the degrading time of carbon which is nearly constant.In this way half of this half portion is calculated and the process goes on till we dont find the exact age of the item.As radioactive Parent atoms decay to stable daughter atoms (as uranium decays to lead) each disintegration results in one more atom of the daughter than was initially present and one less atom of the parent.The probability of a parent atom decaying in a fixed period of time is always the same for all atoms of that type regardless of temperature, pressure, or chemical conditions. The time required for one-half of any original number of parent atoms to decay is the half-life, which is related to the decay constant by a simple mathematical formula.This is a way to measure the proportions of a daughter isotope and the parent radioisotope of some element trapped inside a rock since the time the rock formed.

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