The illustration below shows the three isotopes of carbon.Some isotopes of certain elements are unstable; they can spontaneously change into another kind of atom in a process called “radioactive decay.” Since this process presently happens at a known measured rate, scientists attempt to use it like a “clock” to tell how long ago a rock or fossil formed.
The number of neutrons in the nucleus can vary in any given type of atom.
“If you’re trying to look at archaeological sites at the order of 30,000 or 40,000 years ago, the ages may shift by only a few hundred years but that may be significant in putting them before or after changes in climate,” he says.
Take the extinction of Neanderthals, which occurred in western Europe less than 30,000 years ago.
Protons and neutrons make up the center (nucleus) of the atom, and electrons form shells around the nucleus.
The number of protons in the nucleus of an atom determines the element.