I. What is the Geologic Time
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.
I. What is The Geologic Time
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.
Why do Geologists have the time
It helps break it up into manageable
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
B. Eras are divided into
periods (except for
C. Cenozoic periods are divided
III. Geologic Eras
1. Earth forms including
seas & mountains
2. Few fossils of jellyfish,
worms, bacteria, algae,
How do you date rocks that
don’t have organisms in it?
Any rock/fossil that is over
B. Paleozoic – 6 periods
1. Invertebrates most common
2. Vertebrates – fish and
3. Plants – ferns and trees in