Some chemical elements have more than one type of atom. Carbon has two stable, nonradioactive isotopes: carbon-12 (12C), and carbon-13 (13C).In addition, there are trace amounts of the unstable isotope carbon-14 (14C) on Earth.Materials that originally came from living things, such as wood and natural fibres, can be dated by measuring the amount of carbon-14 they contain.

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Carbon-14 has a relatively short half-life of 5730 years, meaning that the amount of carbon-14 in a sample is halved over the course of 5730 years due to radioactive decay.

By about ten half-lives, or 58,000 years, the amount of carbon-14 left in the fossil is very little- about 1/1000 of the original number of carbon-14 atoms in the fossil.

Later called Ötzi the Iceman, small samples from his body were carbon dated by scientists.

The results showed that Ötzi died over 5000 years ago, sometime between 33 BC. It is found in the air in carbon dioxide molecules.

The amount of carbon-14 in the air has stayed the same for thousands of years.

There is a small amount of radioactive carbon-14 in all living organisms because it enters the food chain.Plants take in atmospheric carbon dioxide by photosynthesis, and are ingested by animals.So, every living thing is constantly exchanging carbon-14 with its environment as long as it lives. The carbon in its body will remain until it decomposes or fossilizes.Isotopes participate in the same chemical reactions but often at differing rates.When isotopes are to be designated specifically, the chemical symbol is expanded to identify the mass (for example, C is not stable.The amount of carbon-14 gradually decreases through radioactive beta decay with a half-life of 5,730 years.