Answer:
Step-by-step explanation:
Certain fossils, such as ammonites, trilobites and graptolites, are known as index fossils. Because they were so abundant and widespread during a short period of geological time, their presence helps date rocks from that period.
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. HOPED THIS HELPED, FEEL FREE TO ASK ANY QUESTIONS>