1. I. What is the Geologic Time
Scale?
a. Based on their interpretations of the
rock record, geologists have divided
Earth’s 4.56-billion-year history into units
that represent specific amounts of
time. Taken together, these time spans
make up the geologic time scale.

3. I. What is The Geologic Time
Scale
b. The geologic time scale is divided into
sections based on fossil evidence.
c. Organisms have become more
complex over time.
d. Geologic time divisions represent
changes in the fossil evidence.

4. Extra
Why do Geologists have the time
scale?
It helps break it up into manageable
parts!

7. II.Measuring Geologic Time
A. Eras (largest divisions)
1. Precambrian – earliest,
4 billion years
2. Paleozoic – 345 million years
3. Mesozoic – 160 million years
4. Cenozoic – current, so far
65 million years

8. B. Eras are divided into
periods (except for
Precambrian)
C. Cenozoic periods are divided
into epochs

10. III. Geologic Eras
A. Precambrian
1. Earth forms including
seas & mountains
2. Few fossils of jellyfish,
worms, bacteria, algae,
& fungi

11. Extra
How do you date rocks that
don’t have organisms in it?
URANIUM’s-Lead’s Half-Life
Any rock/fossil that is over
50,000 years!

12. B. Paleozoic – 6 periods
1. Invertebrates most common
a. Trilobites
b. Brachiopods
2. Vertebrates – fish and
amphibians
3. Plants – ferns and trees in
swampy areas

13. Trilobite

14. Trilobite

15. Trilobite

16. Brachiopods

17. Brachiopods

18. Brachiopods

19. Eryops
Eryops

20. Eryops

21. Eryops

22. C. Mesozoic – 3 periods
1. Pangaea began to break
apart
2. Cycads & conifers evolved
3. “Age of the Reptiles”
4. Dinosaurs became extinct

24. Tyrannosaurus rex

25. Cycads

26. D. Cenozoic – 2 periods
1. “Age of Mammals”
2. At least 4 ice ages

27. Question of the Day
How would a new
era start?!?!

28. Science Attack