Question

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

Scientists developed the geologic time scale as they studied rock layers and index fossils.
The fossil record helps scientists describe life only in the seas and other bodies of water.
Precambrian time is the most recent time in Earth’s history.
Precambrian time makes up 88 percent of Earth’s history.
The first birds appeared during the Mesozoic Era.
The basic units of the geologic time scale are periods, eras, and centuries.
Humans appeared during the Cenozoic era.

Answer 1

True statements:
- Scientists developed the geologic time scale as they studied rock layers and index fossils. (True — stratigraphy and fossils were key to building the scale.)
- Precambrian time makes up 88 percent of Earth’s history. (True — the Precambrian spans from Earth's formation to the start of the Cambrian and covers roughly 88% of geologic time.)
- The first birds appeared during the Mesozoic Era. (True — early birds evolved in the Mesozoic, e.g., Archaeopteryx.)
- Humans appeared during the Cenozoic era. (True — humans evolved during the Cenozoic, in the Quaternary period.)

False statements:
- The fossil record helps scientists describe life only in the seas and other bodies of water. (False — it documents life on land and in water.)
- Precambrian time is the most recent time in Earth’s history. (False — Precambrian is the oldest/earliest part of Earth history.)
- The basic units of the geologic time scale are periods, eras, and centuries. (False — basic units include eons, eras, periods, epochs, and ages; centuries are not a geologic unit.)