Index fossils are remains of organisms that lived for a short period of time. Thus, index fossils help scientists date fossils and geological features based on relative dating. Such fossils are usually marine organisms. After dying, such organisms were covered with sediments and fossilized within sedimentary rock. If the era during which the index fossil lived is known, then it can be speculated that other organisms or geological features that are found in the same strata as the index fossil lived or were created during the same time period. Examples of five characteristics of a good index fossil are identified and briefly explained below.
- A good index fossil lived for a short period of time so that the range of ages of the strata in which the index fossil is located is also small.
- A good index fossil is found in a wide geological range. Scientists look for fossils all across the world. If a new fossil is found in the same strata as an index fossil, then the new fossil’s age can be correlated to time period during which the index fossil lived.
- In order to be located in strata within differing parts of the world or a country, good index fossils have to have been abundant while on Earth.
- A good index fossil needs to have definitive characteristics so that it can be easily identified by paleontologists.
- A good index fossil cannot easily decompose. This would prevent the organism from becoming a fossil.