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.
Eon definition: An indefinitely long-period of time; an age.; An indefinitely long-period of time; an age.; The longest unit of geologic time, containing two or more eras.; The longest unit of geologicâ¦