I fossil index is used to determine the geographic time period a particular fossil was in existence. The index is formed by where the fossil lies in the sediment. The higher the fossils are in the sediment, the younger the fossil is. The lower the fossils are in the sediment, the older they are. Scientists study fossil in the fossil index to see what types of animals were in existence during certain time periods. Important things (or characterstics) that scientists look for in creating a fossil index are the abundance of the fossil, physical features of the species, evolution and extinction of the species. Abundance is key for understanding when that species existed. Scientists look in multiple locations for a fossil to see if they are present in multiple regions during the same time period. Scientists must also be able to denote the physical features of the fossil in order to classify the type of organism. Extinction and evolution are important to understanding the life span of the organism in the fossil. Scientists also can determine the evolutionary linage of other organisms as well. Fossil record is important record of evolutionary time.
Characteristics of the best ideal index fossils are abundant, easy to identify, rapid evolution and extinction and widely distributed.