Eras of Earth’s History
Answer Key
9. Quaternary Period
1. Answers will vary. Both students’ timelines
may show segments are divided into similar
periods, or that the timelines represent a
person in the same type of profession, such
as an athlete or scientist. They may show
different time sections and different types of
events that represent the person they chose.
10. f
11. c
12. e
13. a
14. d
15. b
1. Evidence includes the fossil record, which
2. Answers will vary. Sample: Timelines are
shows many organisms died out 65 million
years ago, an impact crater near the Yucatán
Peninsula, and a layer of rock around Earth that
is enriched with iridium.
outlines of events during certain periods of
time. Details about each event would make
the timeline too cumbersome.
3. Answers will vary. Students may show key
2. Evidence includes the fossil record, which shows
accomplishments that appear in a different
order from how they occurred in time.
many organisms died out 65 million years ago,
a huge area of volcanic rock on the Indian
subcontinent from 65 million years ago, and a
layer of rock around Earth that is enriched with
iridium.
4. Answers will vary. Students may choose a
timelines because it shows the order in time
that the events happened. Some students
may choose the event list to show the most
important items first.
3. In each theory, a dust cloud blocks the energy
from the sun from reaching Earth’s surface for
months or longer. This causes plants, which use
energy from the sun to make food, to die, and
then animals die.
For much of Earth’s history, the only form of life
was single-celled organisms. Finally invertebrates
and vertebrates developed. Plants, fishes,
amphibians, and reptiles followed. Mammals,
birds, and flowering plants evolved before human
beings developed on Earth.
4. Answers may vary. A typical answer might
suggest that there is no evidence that could
prove absolutely that one or the other of these
theories is true.
5. Answers may vary. A typical answer might
suggest that the asteroid theory makes more
sense because volcanic eruptions in recent times
have not caused similar extinctions.
1. Silurian Period
2. Paleozoic Era
3. Devonian Period
1. true
2. invertebrate
4. Permian Period
3. true
4. true
5. Mesozoic Era
5. vertebrates
6. true
6. Cretaceous Period
7. mass extinction
8. Reptiles
7. Triassic Period
9. mammals
8. Cenozoic Era
139H
10. Quaternary Period