Answer:
Carbon atoms are contained in most cells of all living things on Earth. Most carbon atoms (98.89 percent) are called carbon-12 because they have 6 neutrons and 6 protons in their nuclei. Most of the remaining atoms (1.11 percent) have 7 neutrons along with their 6 protons and are called carbon-13 atoms, but a very small quantity (called a trace amount) of carbon atoms have 8 neutrons and 6 protons. These and are called carbon-14 atoms.
Carbon-14 atoms are radioactive and are referred to as radiocarbon. They are unstable, and decay slowly by releasing electrons before evolving into nitrogen-14 atoms. A living organisms constantly absorbs carbon in its body systems by respiration and processing nutrients, and the amount of carbon-14 it contains remains fairly constant for as long as it lives. The carbon-14 decays without being replaced after the organism dies and half of the carbon-14 nuclei will disintegrate in about 5,730 years. The amount of carbon-14 that has disintegrated in a fossilized organism can be calculated and used for determining its age.