Carbon-14 has six protons and eight neutrons in its nucleus. By contrast, most of the carbon in our bodies and in the outside world, known as carbon-12, has six protons and six neutrons. Crucially, those two extra neutrons make the nucleus of a carbon-14 atom unstable so that it decays radioactively into an atom of nitrogen. More importantly, these decays are relatively infrequent so that it is possible to measure changes in a carbon sample over tens of thousands of years.

What are carbon dating, isotopes and half-lives?

The nucleus of an element is made up of subatomic particles: protons and neutrons. The number of protons in the nucleus of an element defines its chemical behavior. But atoms of the same element can possess different numbers of neutrons in their nuclei. These different forms are known as isotopes.

Carbon has three main isotopes: carbon-12, carbon-13 and carbon-14. The first two are stable but the last decays radioactively.

In any sample, carbon-14 atoms will take around 5,730 years to lose half their number. Thus carbon-14 is said to have a half-life of 5,730 years.

Applications

Over the years, uses of carbon-14 have spread well beyond dating ancient artefacts. Drugs can be labelled with carbon-14 and followed as they pass through the body in order to test their safety and efficacy. Other researchers have used the isotope to trace the way in which plants convert carbon dioxide into sugar, revealing the intricate processes underpinning photosynthesis.

In addition, carbon-14 has been exploited to study plankton and other forms of sea life, revealing how the waters of the oceans circulate in a great interconnected web of currents that sweep round the planet. “The carbon content of a fish will register what it has been eating, which in turn will reflect the chemistry of the surrounding water, which will be influenced by how the ocean has mixed,” says Marra. For good measure, carbon-14 is now playing a major role in uncovering how climates have changed on Earth over tens of thousands of years, work of immense importance as scientists struggle to understand how rising carbon emissions are now triggering dangerous global heating.