follow Dictionary.com

How Well Do You Know English Slang?

index fossil

noun, Geology, Paleontology
1.
a widely distributed fossil, of narrow range in time, regarded as characteristic of a given geological formation, used especially in determining the age of related formations.
Also called guide fossil.
Origin
1895-1900
1895-1900
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
Cite This Source
British Dictionary definitions for index fossil

index fossil

noun
1.
a fossil species that characterizes and is used to delimit a geological zone Also called zone fossil
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Cite This Source
index fossil in Science
index fossil
  (ĭn'děks')   
The fossil remains of an organism that lived in a particular geologic age, used to identify or date the rock or rock layer in which it is found. The best type of index fossils are usually those of swimming or floating organisms that evolved quickly (and therefore did not cover a long span of geologic history) and were able to spread over large areas. Ammonites and graptolites are good index fossils.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
Cite This Source
Encyclopedia Article for index fossil

any animal or plant preserved in the rock record of the Earth that is characteristic of a particular span of geologic time or environment. A useful index fossil must be distinctive or easily recognizable, abundant, and have a wide geographic distribution and a short range through time. Index fossils are the basis for defining boundaries in the geologic time scale and for the correlation of strata. In marine strata, index fossils that are commonly used include the single-celled Protista with hard body parts and larger forms such as ammonoids. In terrestrial sediments of the Cenozoic Era, which began about 66.4 million years ago, mammals are widely used to date deposits. All of these animal forms have hard body parts, such as shells, bones, and teeth, and evolved rapidly.

Learn more about index fossil with a free trial on Britannica.com
Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
Cite This Source

Word of the Day

Difficulty index for index fossil

Few English speakers likely know this word

Word Value for index

13
14
Scrabble Words With Friends