Geologic Principles Notes Right-Side Geologic Principles Notes

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

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

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)

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)

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

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

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

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

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

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

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