1. The Fossil Record Section 17–1
This section explains how fossils form and how they can be interpreted. It also describes the geologic time scale that is used to represent evolutionary time.

2. Fossils and Ancient Life
Scientists who study fossils are called___.
paleontologists

3. Fossils and Ancient Life
What is a fossil record?
It is information about past life that is based on fossils.

4. Fossils and Ancient Life
What evidence does the fossil record provide?
It provides evidence about the history of life on Earth and how different groups of organisms, including species, have changed over time.

5. Fossils and Ancient Life
Species that died out are said to be ___.
extinct

6. Fossils and Ancient Life
Is the following sentence true or false?
About half of all species that have ever lived on Earth have become extinct.
FALSE

7. How Fossils Form
Circle the letter of each sentence that is true about fossils.
Fossils can include footprints, eggs, or other traces of organisms.
The quality of fossil preservation varies.

8. How Fossils Form How do fossils form in sedimentary rock?
Sediments settle to the bottom of lakes and seas and bury dead organisms. The weight of upper layers of sediment compresses lower layers into rock and turns the dead organisms into fossils.

9. Interpreting Fossil Evidence
List the two techniques paleontologists use to determine the age of fossils.
Relative dating
Radioactive dating

10. Interpreting Fossil Evidence
Circle the letter of each sentence that is true about relative dating.
It determines the age of a fossil by comparing its placement with that of fossils in other layers of rock.
It uses index fossils.
It provides no information about absolute age.

11. false The History of Life Is the following sentence true or false?
Older rock layers are usually closer to Earth’s surface than more recent rock layers.
false

12. true The History of Life Is the following sentence true or false?
Scientists use radioactive decay to assign absolute ages to rocks.
true

13. half-life The History of Life
The length of time required for half of the radioactive atoms in a sample to decay is called a(an) _____.
half-life

14. The History of Life
The use of half-lives to determine the age of a sample is called_____.
radioactive dating

15. The History of Life
How do scientists calculate the age of a sample using radioactive dating?
They measure the amount of remaining radioactive isotopes it contains. The smaller the amount, the older the sample.

16. false The History of Life
Is the following sentence true or false? All radioactive elements have the same half-life.
false

17. Geologic Time Scale Era Period
Fill in the missing eras and periods in the geologic time scale below.
Era
Cenozoic
Mesozoic
Paleozoic
Period
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Time
(millions’
of years
ago)
1.8 –
present
65 – 1.8
145 – 65
208 – 145
245 – 208
290 – 245
363 – 290
410 – 363
440 – 410
505 – 440

18. Geologic Time Scale
Circle the letter of the choice that lists the eras of the geologic time scale in order from the most recent to oldest
Cenozoic, Mesozoic, Paleozoic

19. Geologic Time Scale
Circle the letter of each sentence that is true about the geologic time scale.
The scale is used to represent evolutionary time.
Major changes in fossil organisms separate segments of geologic time.