what determines the length of a geologic time period?\no fossil record\no material density\no meteors and…

Brief Explanations:

Geologic time periods are defined based on significant changes in the fossil record, which mark major evolutionary and environmental shifts. Material density, meteors and rocks, and radioactive materials are not the primary determinants of geologic time - period lengths. Radioactive materials are used for dating rocks but not for defining time - period lengths.

Answer:

fossil record