Carbon dating the history of life on earth

Animals incorporate carbon-14 into their bodies by eating plants or other plant-eating animals.Carbon-14 has a half-life of 5,730 years, meaning that after that time, half of the carbon-14 in a sample decays away, according to the University of Arizona.

Atoms are arranged as a nucleus surrounded by an electron cloud, with electrons zinging around at different distances from the nucleus.

The end result: Atoms with six protons and six neutrons — carbon.

While scientists sometimes conceptualize electrons spinning around an atom's nucleus in a defined shell, they actually fly around the nucleus at various distances; this view of the carbon atom can be seen here in two electron cloud figures (bottom), showing the electrons in a single blob (the so-called s-orbital) and in a two-lobed blob or cloud (the p-orbital). It can link to itself, forming long, resilient chains called polymers.

As the sixth-most abundant element in the universe, carbon forms in the belly of stars in a reaction called the triple-alpha process, according to the Swinburne Center for Astrophysics and Supercomputing.

In older stars that have burned most of their hydrogen, leftover helium accumulates.

Carbon-14 is naturally occurring in the atmosphere.