Which statements about geologic time are true? Check the four that apply.

Precambrian time makes up 88% of Earth's history.

The basic units of the geologic time scales are periods, era, and centuries.

Scientists developed the geologic time scale as they studied rock layers and index fossils.

The first birds appeared during the Jurassic period.

The fossil record helps scientists describe life only in the seas and other bodies of water.

Humans appeared during the Cenozoic era.

Precambrian time is the most recent time in Earth's history.