Download 6-1 directed_reading_a 6-1 directed_reading_a

Name ______________________________ Class___________________Date__________________
Worksheet
Directed Reading A
Section: Evidence of the Past
_____ 1. What type of scientists use fossils to reconstruct the history of life
before humans existed?
a. fossilologists
c. sedimentologists
b. dinosaurologists
d. paleontologists
2. What do fossils show us?
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FOSSILS
3. What are fossils?
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Put the three stages of a fossil’s formation in order from first to last. Write the
appropriate numbers from 1 to 3 on the lines provided.
_____ 4. Over time, the mold fills with sediment, which forms a cast of the
organism.
_____ 5. The organism gradually decomposes and leaves a hollow impression,
or mold, in the sediment.
_____ 6. When an organism dies it becomes buried in sediment.
THE AGE OF FOSSILS
7. When scientists look at which layer of rock a fossil is in they are using the
______________________ method of estimating the age of rocks and fossils.
8. When a scientist finds sedimentary rock, where are the oldest layers usually
found? Why?
____________________________________________________________________
____________________________________________________________________
9. Scientists can determine the age of a fossil more precisely than relative dating
using a method called ______________________.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
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The History of Life on Earth
Name ______________________________ Class___________________Date__________________
Directed Reading A continued
10. The particles that make up all matter are called ______________________.
11. As atoms decay what do they release?
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12. The time it takes for half of the unstable atoms in a sample to decay is the
sample’s ______________________.
13. When scientists measure the ratio of unstable atoms to stable atoms in a
sample of rock, what are they trying to determine?
____________________________________________________________________
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THE GEOLOGIC TIME SCALE
14. Why is the earth’s history divided into very long units of time?
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15. The calendar scientists use to outline the history of life on earth is called the
______________________ time scale.
16. After paleontologists have dated a fossil, how do they use the time scale to
help them understand how organisms have changed over time?
_______________________________________________________________
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17. Paleontologists have divided the geologic time scale into blocks of time. The
largest divisions are known as ______________________.
18. Why is the Mesozoic era is referred to as the Age of Reptiles?
_______________________________________________________________
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19. Does the geologic time scale change? Explain why or why not?
_______________________________________________________________
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Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
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The History of Life on Earth
Name ______________________________ Class___________________Date__________________
Directed Reading A continued
20. When a species dies out completely we say it has become
______________________.
21. The periods when many species suddenly become extinct are called
______________________.
22. What are two of the events scientists think could have caused the extinction of
the dinosaurs?
_______________________________________________________________
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THE CHANGING EARTH
_____ 23. Fossils provide evidence that Antarctica was once located
a. at the North Pole.
c. at the South Pole.
b. near the equator.
d. where it is now.
_____ 24. The continents may once have formed one landmass called Pangaea
which means
a. all seas.
c. all Earth.
b. puzzle.
d. landmass.
_____ 25. J. Tuzo Wilson’s theory of how huge pieces of Earth’s crust are pushed
around by forces within the planet is called
a. continents.
c. plate tectonics.
b. crust tectonics.
d. Pangaea.
_____ 26. According to the theory of plate tectonics, how many large rigid plates
are there?
a. five
c. eight
b. two
d. seven
27. How do slow changes, such as moving continents, affect organisms differently
than rapid changes, such as a meteorite impact, affect organisms?
_______________________________________________________________
_______________________________________________________________
28. Why are fossils found in some places very different from the organisms now
living in the same area?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
3
The History of Life on Earth