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 (plural eons) ( 1 US) Eternity. 2  A period of 1,000,000,000 years. 2012 January 1, Robert L. Dorit, âRereading Darwinâ, in American Scientist, volume 100, number 1, page 23: We live our lives in three dimensions for our threescore and ten allotted years. ( 3 geology) The longest time period used in geology.