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Geologic Time Scale
Use with Chapter 14, Section 14.1
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RETEACHING SKILLS TRANSPARENCY MASTER 23 BIOLOGY: The Dynamics of Life
Name Date Class
Geologic Time Scale
Use with Chapter 14, Section 14.1
1. What is the basis of the Geologic Time
Scale?
When the geological record was divided into time units that were related based on the
similar relation of the rock formations.
2. Describe the divisions of the Geologic
Time Scale.
1. Precambrian Era
2. Paleozoic Era - Cambrian
Mississippian
- Ordovician
Pennsylvanian
- Silurian
-Permian
- Devonian
3. Mesozioc - Triassic
- Jurassic
- Cretaceous
4. Cenozoic - Tertiary
- Quaternary
3. During what era and
at approximately what date does fossil evidence
suggest life had evolved on Earth? What form of life was this?
According to fossils, a large number of animals (including the distant
ancestors of many modern animals) evolved between 530 and 520 million years
ago.

4. What forms of living things characterized the
Cambrian period?
Invertebrates were the forms of living things that
characterized that Cambrian period.
5. During what era did the first vertebrates evolve? What were
these vertebrates?
Paleozoic Era: Vertebrates (including fish, amphibians, and reptiles)
began to flourish in the later Paleozoic. Animals and plants
populated the land (but many still lived in the ocean!).
6. The dinosaurs and many other species became extinct in a relatively short
period of time that marks what is called the K-T boundary, which stands
between the Cretaceous and Tertiary periods. About how long ago did the
dinosaurs become extinct?
The dinosaurs became extinct around 61 - 66 million years ago.
7. Imagine you found a fossil of a bird that dates to 213 million years. Why
would this find be astonishing to scientists?
Finding a fossil of a bird that dates back to 213 million years would be
astonishing to scientists because that would be the Triassic period, the
period before the first birds had evolved.
8. Suppose a geologist finds a layer of rock that can be dated to 320
million years ago. Layers from which periods would be expected to be
above and below the newly discovered layer?
Layers of rock from the periods Pennsylvanian and Mississippian would be expected to be above
and below the newly discovered layer.