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.
In Astronomy, an eon refers to 1 billion (10^9) years. But it also refers to a very long, unspecified period of time, or specific geologic stages of the Earth. Since this question is posted in Astronomy, I will assume that the answer of eon = 10^9 years is the most appropriate, however it is not the most common. The term eon (or aeon) is frequently used as a term for a very long but un-specified time period, much the same way forever and ages are used.