Which statements about geologic time are true? Check all that apply. 1 Scientists developed the geologic time scale as they studied rock layers and index fossils.

2 The fossil record helps scientists describe life only in the seas and other bodies of water.
3 Precambrian time is the most recent time in Earth’s history.

4 Precambrian time makes up 88 percent of Earth’s history.

5 The first birds appeared during the Jurassic period.

6 The basic units of the geologic time scale are periods, eras, and centuries.

7 Humans appeared during the Cenozoic era.