We are fortunate that here in Montana there are many places where we have Mesozoic age rocks exposed at the surface of the ground. The sediments found at the surface of the ground are named according to rock type and relative position with other sediments. The basic sedimentary unit is a formation, which is a mappable rock unit definable by distinctive upper and lower boundaries. Determining the ages of particular formations, and therefore, how formations relate to one another in time, we rely on radioactive age dates. Determining the age of a rock unit.
All matter is made up of chemical elements, each of which is composed of atoms.
The nucleus of an atom is composed of protons and neutrons. The combined number of protons and neutrons in an atom is its atomic mass number. Isotopes 12 and 13 are stable, but 14 is unstable. In Montana there are numerous formations deposited during the Mesozoic Era. Many of these formations have yielded dinosaur remains.