1. Geologic Principles Notes
Right-Side
Geologic Principles Notes

2. 2/23/12
Get Ready to take “Geologic Timescale Notes” on the next clean right side page of your notebook!

3. They help geologists divide Earth’s history into time units
How are fossils useful to us?
They help geologists divide Earth’s history into time units
Ancient fossil and rock data provide relative dates of past events
The rock record has contributed to our modern day geologic time scale, a record of Earth’s history from 4.6 bya to the present

4. Eons= largest division (billions of years)
How do we divide geologic time?
Eons= largest division (billions of years)
Era= hundreds of millions of years; based on fossilized life forms found in rocks
Cenozoic (recent life)
Mesozoic (middle life)
Paleozoic (ancient life)

5. Epochs= smallest division (millions of years)
How do we divide geologic time?
Periods= tens of millions of years; based on life forms that were abundant OR became extinct
Epochs= smallest division (millions of years)
ONLY in the Cenozoic Era because rocks and fossils are more easily accessed (not buried or destroyed)

7. Principle of Uniformitarianism
Why does Earth’s surface change?
Principle of Uniformitarianism
The processes occurring on Earth today have been occurring since it formed, BUT the rate and intensity have changed
Ex: erosion, earthquakes, sea levels

8. Principle of Original Horizontality
Why are rocks striped?
Principle of Original Horizontality
Sedimentary rocks are deposited in nearly horizontal layers

9. Principle of Superposition
How do we know relative age?
Principle of Superposition
Oldest rocks are on the bottom, each successive layer is younger

10. Principle of Faunal Succession
How do we know relative age?
Principle of Faunal Succession
Oldest fossils are in the bottom layers, successive layers are younger

11. Principle of Cross-Cutting Relationships
How do we know relative age?
Principle of Cross-Cutting Relationships
An intrusion is younger than a rock it cuts across
youngest

12. Unconformities Layers get shifted up or down
What about gaps in the rock record?
Unconformities
Layers get shifted up or down
Layers get eroded

13. Correlation= matching rock regions in one area to another area
Why does it matter???
Correlation= matching rock regions in one area to another area
Helps determine sequence of events in Earth’s history