Radioactive decay is the emission of energy in the form of ionizing radiation. Ionizing radiation can affect the atoms in living things, so it poses a health risk by damaging tissue and DNA in genes.. The ionizing radiation that is emitted can include alpha particles.   Radioactive Dating: Radioactive isotopes can be used to estimate the ages of fossils and rocks. The method is called radioactive dating.     Carbon-14 dating is an example of radioactive dating. Carbon-14 forms naturally in Earth's atmosphere when cosmic rays strike atoms of nitrogen-14. Living things take in and use... Show more

Radioactive decay is the emission of energy in the form of ionizing radiation. Ionizing radiation can affect the atoms in living things, so it poses a health risk by damaging tissue and DNA in genes.. The ionizing radiation that is emitted can include alpha particles.
 

Radioactive Dating: Radioactive isotopes can be used to estimate the ages of fossils and rocks. The method is called radioactive dating.    
Carbon-14 dating is an example of radioactive dating. Carbon-14 forms naturally in Earth's atmosphere when cosmic rays strike atoms of nitrogen-14. Living things take in and use carbon-14, just as they do carbon-12. The carbon-14 in living things gradually decays to nitrogen-14. However, it is constantly replaced because living things keep taking in carbon-14. As a result, there is a fixed ratio of carbon-14 to carbon-12 in organisms as long as they are alive.    
After organisms die, the carbon-14 they already contain continues to decay, but it is no longer replaced. Therefore, the carbon-14 in a dead organism constantly declines at a fixed rate equal to the half-life of carbon-14. If you measure how much carbon-14 is left in a fossil, you can determine how many half-lives (and how many years) have passed since the organism died.

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