Elements occur naturally in the earth, and they can tell us a lot about our Earth's past. Carbon, uranium and potassium are just a few examples of elements used in radioactive dating.
Each element is made up of atoms, and within each atom is a central particle called a nucleus. Within the nucleus, we find neutrons and protons; but for now, let's just focus on the neutrons. These neutrons can become unstable, and when they do, they release energy and undergo decay. Scientists call this behavior radioactivity.
Radioactivity occurs when the nucleus contains an excess amount of neutrons. When an atom varies in the number of neutrons, the variation is called an isotope. Isotopes are unstable forms of elements. During radioactivity, the unstable isotope breaks down and changes into a different substance. A new, more stable isotope, called the decay or daughter product, takes its place. The isotope doesn't actually deteriorate; it just changes into something else.