CARBON DATING

We know that plants uses carbon(in the form of carbon dioxide) to carry out photosynthesis.But they also absorbs a radio active form of carbon dioxide, which is continuously created in the earth's atmosphere due to the collision of cosmic rays with carbon dioxide molecules.When animals eat plants it enters in their bodies and cycles all over the food chain .The radio active carbon or radiocarbon stays on the plant or animal body,even when they are dead,but under go radioactive decay with time.By calculating the percentage of radio carbon in a piece of old wood or fragment of bone scientist can know the age of organic substances.