Question

what determines the length of a geologic time period?
o fossil record
o material density
o meteors and rocks
o radioactive materials

Explanation:

Geologic time periods are defined based on significant changes in the fossil record. Fossils provide evidence of the appearance, evolution, and extinction of different organisms over time, which helps in marking the boundaries of geologic time periods. 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 the length of a geologic time period in terms of its start and end.

Answer:

A. fossil record