GENERAL GEOLOGY

Detailed explanation-1: -A useful index fossil must be distinctive or easily recognizable, abundant, and have a wide geographic distribution and a short range through time.

Detailed explanation-2: -Because they were mobile animals, they tended to inhabit large, even global areas. They were also hard-shelled invertebrates, so they fossilized easily. These fossils are large enough to study without a microscope.

Detailed explanation-3: -Different species of trilobite fossils can be used to narrow the age even more. Trilobites are good index fossils.

Detailed explanation-4: -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. Living fossils are organisms that haven’t changed much in millions of years and are still alive today.

Detailed explanation-5: -Some fossils, called index fossils, are particularly useful in correlating rocks. For a fossil to be a good index fossil, it needs to have lived during one specific time period, be easy to identify and have been abundant and found in many places. For example, ammonites lived in the Mesozoic era.