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. Scientists calculate ages by measuring how much of the isotope remains in the substance.
The key to an age of a substance is the decay-product ratio. The ratio of the original isotope and its decay product determines how many half-lives have occurred since the sample formed. A half-life measures the time it takes for one half of a radio isotope's atoms to break down into another element. 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. This process begins as soon as a living thing dies and is unable to produce more carbon-14. Plants produce carbon-14 through photosynthesis, while animals and people ingest carbon-14 by eating plants.
Carbon-14 has a half-life of 5,730 years. Scientists determine the ages of once-living things by measuring the amount of carbon-14 in the material. For biological objects older than 50,000 years, scientists use radioactive dating to determine the age of rocks surrounding where the material was found. By dating rocks, scientists can approximate ages of very old fossils, bones and teeth.
Radiocarbon dating was invented in the 1940s by Willard F. Libby. Radioactive dating is used in research fields, such as anthropology, palaeontology, geology and archeology.