GEOLOGY

Detailed explanation-1: -Fossil species that are used to distinguish one layer from another are called index fossils. Index fossils occur for a limited interval of time. Usually index fossils are fossil organisms that are common, easily identified, and found across a large area.

Detailed explanation-2: -index fossils are fossils that are useful for dating and correlating the strata in which it is found. Usually the animal was only in there for a short period of time. These fossils are mainly used by geologists to determine the age of the animals departure.

Detailed explanation-3: -Ammonites, trilobites, and graptolites are often used as index fossils, as are various microfossils, or fossils of microscopic organisms.

Detailed explanation-4: -Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation. Index fossils are fossils that are known to only occur within a very specific age range.

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.