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.
For other uses, see Eon (disambiguation). Eon is a 1985 science fiction novel by Greg Bear. It is the first story written in The Way fictional universe. Events in Eon take place in 2005, when the U.S. and U.S.S.R. are on the verge of nuclear war. In that tense political climate, a 290 km asteroid is detected, following an anomalous and very powerful energy burst just outside the solar system.