Floridaâs tract of coral reefs has the honor of being the third-largest barrier reef ecosystem in the world. However, it could soon be a thing of the past, as the acidification of the oceanâs water is dissolving it faster than it can rebuild.
index (plural indexes or indices) 1  An alphabetical listing of items and their location. The index of a book lists words or expressions and the pages of the book upon which they are to be found. 2  The index finger; the forefinger. 3  A movable finger on a gauge, scale, etc.
â¢ INDEX FOSSIL (noun) The noun INDEX FOSSIL has 1 sense: 1. a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found. Familiarity information: INDEX FOSSIL used as a noun is very rare.