Which of these is true about index fossils? a) are scarcely found b) used as guides in relative dating c) found in the youngest layer of the rock d) used as reference points in absolute dating

D) Used as reference points in absolute dating

Explanation:

Strictly speaking, the term index fossil is used in stratigraphy to designate fossils from taxonomic groups (usually of the genus or species category) on the basis of which biozones are defined, for relative dating of geological strata. In other words, these fossils are used as reference points in absolute dating.

In a broader, informal way, the term index fossil (or old fossil, characteristic fossil or stratigraphic fossil) is often used to generically designate the fossils of taxonomic groups that allow for finer, more detailed relative dates, or to identify specific biostratigraphic interval.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

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