How is fossil evidence used to determine relative age of rocks?

Certain fossils, called index fossils, help geologists match rock layers. To be useful as an index fossil, a fossil must be widely distributed and represent a type of organism that existed for a brief time period. Index fossils are useful because they tell the relative ages of the rock layers in which they occur. I hope this helped!

Asmall closed hole formed in an outwash plain or moraine. forms when a  glacier retreats then remains stationary. 

Answerwill have thinner; have thicker oceanic sediments;