Question

1. which best identifies specific geologic eras throughout earths history?index fossilsoxygen levelsmeteor impactsland mass size

Explanation:

Index fossils are fossils that are used to define and identify geologic periods (or faunal stages). They have a short vertical range (limited to a particular geological time) and a wide geographic distribution. Oxygen levels, meteor impacts, and land - mass size are not as specific or widely used as index fossils for identifying specific geologic eras.

Answer:

index fossils