Carbon dating uses an isotope of the element carbon. The most common form of carbon has 6 protons and 6 neutrons. It is called carbon-12. Carbon-14 is an isotope of carbon that has 8 neutrons. The extra neutrons make carbon-14 unstable, or radioactive. Atoms that are unstable tend to break apart. This process is called radioactive decay. All living organisms contain carbon. Plants get carbon from the atmosphere. Animals get carbon from food. Most of the carbon is carbon-12, but some of it is carbon-14. Carbon cycles through living things while they are alive. The ratio of carbon-12 to carbon-14 remains the same while a plant or animal is alive. When the plant or animal dies, the carbon-14 begins to decay. By comparing the ratio of carbon-12 to carbon-14, scientists can tell how long the plant or animal has been dead. To determine the absolute age of rocks and fossils, scientists use:
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The difference between the amounts of carbon-12 and carbon-14.
The ratio between carbon-12 and carbon-14
The difference between the number of protons and neutrons in carbon-14.