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.

Explanation:

1. For "Scientists developed the geologic time scale as they studied rock layers and index fossils": Scientists study rock layers (stratigraphy) and index fossils to establish the geologic time scale, so this is true.
2. For "The fossil record helps scientists describe life only in the seas and other bodies of water": The fossil record includes terrestrial (land - based) organisms too, so this is false.
3. For "Precambrian time is the most recent time in Earth’s history": Precambrian is one of the earliest time periods, not the most recent, so this is false.
4. For "Precambrian time makes up 88 percent of Earth’s history": Precambrian time spans about 88% of Earth's total history, so this is true.
5. For "The first birds appeared during the Mesozoic Era": Archaeopteryx (first bird - like creature) appeared in the Mesozoic Era, so this is true.
6. For "The basic units of the geologic time scale are periods, eras, and centuries": The basic units are eons, eras, periods, epochs, not centuries, so this is false.
7. For "Humans appeared during the Cenozoic era": Humans (Homo sapiens) appeared in the Cenozoic era, so this is true.

Answer:

• Scientists developed the geologic time scale as they studied rock layers and index fossils.
• Precambrian time makes up 88 percent of Earth’s history.
• The first birds appeared during the Mesozoic Era.
• Humans appeared during the Cenozoic era.