All atoms of a given element contain the same number of protons. Atoms of an element with different numbers of neutrons are called isotopes. The half-life is the time it takes for half of a given amount of an isotope to decay.

Only a tiny percentage of carbon atoms are carbon-14. Figure below shows carbon dioxide, which forms in the atmosphere from carbon-14 and oxygen.

For instance, if an object has 50 percent of its decay product, it has been through one half-life.

A popular way to determine the ages of biological substances no more than 50,000 years old is to measure the decay of carbon-14 into nitrogen-14.

Imagine that you start out with 100 grams of carbon-14. Figure below graphs the rate of decay of carbon-14.Radioactive dating uses the decay rates of radioactive substances to measure absolute ages of rocks, minerals and carbon-based substances, according to How Stuff Works.Scientists know how quickly radioactive isotopes decay into other elements over thousands, millions and even billions of years.We can estimate the amount of carbon-14 that has decayed by measuring the amount of carbon-14 to carbon-12. With this information, we can tell how long ago the organism died. It decays quickly compared to some other unstable isotopes.

So carbon-14 dating is useful for specimens younger than 50,000 years old. But radiocarbon dating is very useful for more recent events.

Radiocarbon dating was invented in the 1940s by Willard F. Radioactive dating is used in research fields, such as anthropology, palaeontology, geology and archeology.

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