GEOLOGY

Detailed explanation-1: -Index fossils are fossils that are widespread but only existed for a short period of time. Index fossils help scientists to find the relative age of a rock layer and match it up with other rock layers.

Detailed explanation-2: -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 65.5 million years ago, mammals are widely used to date deposits.

Detailed explanation-3: -Index fossils (also known as guide fossils or indicator fossils) are fossils used to define and identify geologic periods (or faunal stages). Index fossils must have a short vertical range, wide geographic distribution and rapid evolutionary trends.

Detailed explanation-4: -Index fossils are of organisms that lived over a wide area. They lived for a fairly short period of time.