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Relative dating/ Geologic Laws
Transcript of Relative dating/ Geologic Laws
"the present is the key to the past"
PRINCIPLES OF GEOLOGIC HISTORY
Principle of inclusions
All the geological processes (Weathering, Erosion, Volcanism, Earthquakes, etc.) that occur today also occurred in the past in the same ways
Sediments are deposited in flat lying or horizontal layers that are parallel to the surface on which they weredeposited
If rocks are
they have been deformed
States that the rock layers on the bottom are oldest, the rock layers on the top are youngest.
If something (such as faults, cracks, veins, intrusions, or extrusions) cuts through rock layers, the rock layers themselves must be older than the thing cutting through them.
Pieces of rock found in other layers
are ALWAYS older.
Folding always happens AFTER the layers have been deposited. Caused by Tectonic Activity--stress on the plate by convection currents squeezing on the plate.
Deposition -> Tilt -> Erosion -> Deposition
Deposition -> Erosion -> Deposition
Igneous/ Metamorphic rock -> Erosion -> Deposition
Missing rock layers show missing time.
Caused by episodes of crustal deformation, erosion and sea level variations.
Usually shown with a wavy line
Siccar Point, Scotland Hutton's Unconformity
PB & J Analogy
The way I make a PB & J sandwich is the same now as when my parents made it for m e ( Uniformatarianism)
The bread had to be flat for me to spread the peanut butter on it (Original Horizontality)
The piece of bread on top has been a part of the sandwich for less time than the bottom piece of bread ( Superposition)
If I slice the sandwich, all those layers (PB, J, and bread) had to be there before I cut into the sandwich (Cross Cutting Relationship)
If I use chunky peanut butter the peanut pieces had to have been there first (Inclusions)
If I fold the sandwich all the layers had to have been there first (Folding)
If I remove the jelly and add more peanut butter a step (part of time) will be missing (Unconformity
1. What is the purpose of the geologic time scale?
2. What did we do last class period with the cash register paper and why?
3. Place the time divisions in the correct order.
precambrian cenozoic mesozoic paleozoic