Nature leaves its traces in the form of isotopes. In today’s column, Sara Abril explains carbon-14, a biology tool used to determine the age of organic samples.

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Radioactive carbon 14 isotope, a very important tool in biology, is the most reliable technique to detect the age of organic samples older than 50 thousand years.

Let us remember that isotopes are atoms of the same element but with different atomic mass. They differ from each other by the number of neutrons.

Isotopes can be stable, remaining stable over time, or unstable, which degrade or decay and become particles or radiation: these are the radioactive isotopes.

Carbon 14 is a radioactive isotope of carbon. Carbon always has six protons, but it can have six neutrons, as is the case with carbon 12, which is one of the stable isotopes.

In the case of carbon 14, which has 8 neutrons, it is unstable, decays to nitrogen 14 and emits beta radiation.

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Carbon 14 is naturally in the atmosphere mixed with carbon 12 in different proportions throughout history.

When organisms photosynthesize, they acquire that same proportion of carbon-14 and maintain it until they die. However, when they die, the isotope decays, emits beta radiation, converts to nitrogen 14 and decreases in concentration.

We know that an organism decreases its amount of carbon-14 by half in about 5,700 years. If the radiation is also measured, the time at which the organism died can be determined: this is called radiocarbon dating and is done especially for plants and photosynthetic organisms, but it is also useful for animals because they consume plants.

This development earned Willard Frank Libby the Nobel Prize in chemistry in 1960.

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