1 Simple molecules [molecule: A molecule is a collection of two or more atoms held together by chemical bonds. 2  It is the smallest part of a substance that displays the properties of the substance.
Eon has a number of meanings. In Astronomy, an eon refers to 1 billion (109) years. But it also refers to a very long, unspecified period of time, or specific geologic stages of the Earth.
1 An example of an eon is the amount of time since dinosaurs roamed the earth. 2  an extremely long, indefinite period of time; thousands and thousands of years. 3  Geol.  the major unit of geologic time, usually subdivided into eras.