Directed Reading
Name ____________________
Section: Geologic Time
1. Where can we find evidence of changes in conditions on Earth’s surface?
2. What is the purpose of the geologic time scale?
3. The ordered arrangement of rock layers is called a(n) _______________________ .
4. In a geologic column, the oldest rocks are located at the _________________________of the column.
5. How do the fossils in the upper layers of a geologic column differ from those in the lower, older layers?
6. What method has enabled scientists to determine the ages of rock layers more accurately?
7. Suppose a scientist wants to determine the age of a rock layer with a geologic column. With what does
the scientist compare the rock layer? ____________________________________________________
DIVISIONS OF GEOLOGIC TIME
8. What three indicators do geologists use to divide the geologic time scale into smaller units?
9. How are rocks grouped within each unit of geologic time similar?
10. What does the abbreviation Ma stand for?
11. When did Precambrian time begin?
12. What species were common during the Cambrian Period?
13. What happened to the atmosphere during the Ordovician Period?
14. When did the Silurian Period begin?
15. During which period did the age of fishes begin?
16. In what era was the Carboniferous Period?
17. In North America, into what two periods is the Carboniferous Period divided?
18. What was the dominant life-form of the Jurassic Period?
19. What marked the end of the Mesozoic Era?
20. In which epoch did the age of mammals begin?
21. When did the Eocene Epoch begin?
22. In what epoch did large carnivores appear?
23. In what period was the Pleistocene Epoch?
24. In what epoch did complex human societies develop?
25. The largest unit of geologic time is called a(n) _________________.
26. Name the four eons into which geologic time is divided.
27. When did the present geologic era begin?
28. An era is divided into shorter time units called _______________________ .
29. How do geologic periods get their names?
30. A period may be divided into smaller units called ____________________.
Section: Precambrian Time and the Paleozoic Era
______ 1. What is a nebula?
a. the newly formed sun
b. a large cloud
c. a star
d. a planet
______ 2. When did the Earth form?
a. about 540 million years ago
b. about 4.6 billion years ago
c. after Precambrian time
d. before Precambrian time
______ 3. About how much of Earth’s history occurred during Precambrian time?
a. 20%
b. 40%
c. 50%
d. 88%
______ 4. We know little about Precambrian time because
a. no rocks exist from that time.
b. Earth did not exist.
c. no organisms existed so there are no fossils.
d. Precambrian rocks were damaged and therefore could not be identified.
5. A large area of exposed Precambrian rocks is called a _____________________.
6. How much of the world’s minerals occur in the rocks of Precambrian shields?
7. Precambrian fossils consisting of reeflike deposits formed by blue-green algae are called ____________.
THE PALEOZOIC ERA
______ 8. When the Paleozoic Era began, Earth’s landmasses were
a. arranged much as they are today.
b. located in a single region of the world.
c. unstable due to tectonic activity.
d. scattered around the world.
______ 9. By the end of the Paleozoic Era, Earth’s landmasses had
a. collapsed and dropped below sea level.
b. collided to form a supercontinent called Pangaea.
c. disappeared as a result of tectonic activity.
d. lost all of their mineral deposits.
______ 10. How do Paleozoic rocks differ from Precambrian rocks?
a. Paleozoic rocks contain many fossils.
b. Paleozoic rocks are much older.
c. Paleozoic rocks were formed by tectonic activity.
d. Paleozoic rocks are found only in North America.
______ 11. How many periods is the Paleozoic Era divided into?
a. four
b. six
c. seven
d. three
In the space provided, write the letter of the description that best matches the
term or phrase.
______ 12. brachiopod
______ 13. invertebrate
______ 14. index fossil
______ 15. trilobite
a. a fossil that scientists use to date rocks
b. the most common Cambrian invertebrate
c. a shelled animal common during the
Cambrian Period
d. an animal that does not have a backbone
Section: The Mesozoic and Cenozoic Eras
______ 1. How many marine organisms died at the end of the Permian Period?
a. 50%
b. 78%
c. 90%
d. 100%
______ 2. How many land organisms died at the end of the Permian Period?
a. 50%
b. 78%
c. 90%
d. 100%
______ 3. What occurs during a mass extinction?
a. All species die off.
b. Large numbers of species die off.
c. Organisms adapt to environmental change.
d. Most life-forms survive.
THE MESOZOIC ERA
4. What happened to Pangaea during the Mesozoic Era?
5. What caused mountain ranges to form during the Mesozoic Era?
6. What is another name for the Mesozoic Era?
7. Reptiles that lived in the oceans during the Triassic Period were called ____________________.
In the space provided, write the letter of the description that best matches the
term or phrase.
______ 8. ornithischian
______ 9. Apatosaurus
______ 10. saurischian
______ 11. pterosaur
______ 12. Stegosaurus
a. a “bird-hipped” dinosaur
b. a flying reptile with skin-covered wings
c. a saurischian weighing up to 50 tons
d. a “lizard-hipped” dinosaur
e. one of the best-known ornithischians
13. A dinosaur with a bill like a duck was called the _____________________.
14. The earliest flowering plant, which appeared during the Cretaceous Period, was called a(n) _________.
15. Why have no dinosaur fossils been found in rocks formed after the Cretaceous Period?
16. A substance from meteorites that would have spread over Earth after a large meteorite crash is called
________________________________ .
THE CENOZOIC ERA
17. What happened to Earth’s continents during the Cenozoic Era?
18. What changes have occurred in Earth’s climate during the Cenozoic Era?
19. The period of the Cenozoic Era that includes the time before the last ice age is called the ___________.
20. When did the first primates evolve?
21. What happened to world temperatures at the end of the Eocene Epoch?
22. What caused the uplifting of the Himalayas?
23. Why did many grasses, cone-bearing trees, and hardwood trees grow during the Oligocene Epoch?
25. When did the largest known land mammals live?
26. Why did the sea level fall toward the end of the Pliocene Epoch?
27. Where were fossils of the earliest ancestors of modern humans discovered?
28. When did the Holocene Epoch begin?