Question

natural selection and evolution
which best describes eras and periods?
eras were more recently established on the time scale than periods.
eras have a smaller time span than periods.
eras and periods both appear at the start of the cambrian period.
eras and periods are independent of each other.

Explanation:

Eras are larger - scale divisions of geological time than periods. They are not more recently established, they have a larger time - span, and they are not independent as periods are within eras. The Cambrian period marks the start of the Phanerozoic eon which is divided into eras and periods.

Answer:

None of the provided options are correct.