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: -Characteristics of index fossils: Easily recognizable, short lived (found only in a few layers of rock worldwide), wide distribution (geographic range). Limitations of index fossils: The longer the time period a species lived, the worse the index is.