Geosciences
Geos 170A1 – Lecture 2 : Basic Geological Principles and the Geologist Perspective
As in all sciences, the Scientific Method is key to how we “do” geology.
Recall the pieces of the Scientific Method:
Observations
Ask a question or describe a problem to be addressed
Propose a hypothesis
Make predictions and test them
ITERATE (Science is a process…)
Analyze data
Report Conclusions
In geosciences, observations are key!
Geologists do a lot of field work, looking at rocks, minerals,
layers, mountains, faults, folds, glaciers, corals, and so much more.
Green River, Canyonlands (1871)
Green River, Canyonlands (1968)
Make some observations: Do you see a big geological difference from one picture to the next? (Handout #1)
How fast do things happen on Earth?
James Hutton (18th cent): modern concept of geologic time: Uniformitarianism
All land should be worn flat (by erosion) unless some process renews the landscape by forming new mountains.
“The present is the key to the past”: Geological processes (past and present) are slow.
Examples: Mountains grow mm per year, rocks are eroded mm-cm per year, Earth’s tectonic plates move cm per year.
Hutton came to these ideas by observing slow changes on his own land
James Hutton was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the ‘father’ of modern geology.
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How fast do things happen on Earth?
Example: Mountains grow mm per year…
Let’s work this out: (Handout #2)
Mt. Everest’s peak is 29,028 ft above sea level
How long would it take Mt. Everest to “grow” to
its current height at a rate of mm’s/year?
Step 1:
Let’s round up to 30,000 feet
1 foot = 0.3 meters
1,000 mm = 1 meter
So…30,000 feet = ? mms (work this out)
James Hutton was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the ‘father’ of modern geology.
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How fast do things happen on Earth?
Example: Mountains grow mm per year…
Let’s work this out:
Mt. Everest’s peak is 29,028 ft above sea level
How long would it take Mt. Everest to “grow” to
its current height at a rate of mm’s/year?
Step 2:
We now know that 30,000 feet = ?,000,000 mm
(roughly…using rounding)
IF the mountain grew 3 mm / year, how many
years did it take for Everest to reach its current
height?
(in reality it took much longer and continues to grow today…)
Handout #3 and #4
James Hutton was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the ‘father’ of modern geology.
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Some important principles: “Relative Dating”
youngest
oldest
Original Horizontality- rocks are deposited in horizontal layers
Superposition – rocks at the bottom are the oldest
Tilting/folding is younger than deposition (i.e., it came after)
Faster water flow = more/heavier pieces moved
Water slows/stops = deposition in flat layers
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(Activity #5 – Step 1)
Original Horizontality- rocks are deposited in horizontal layers
Superposition – rocks at the bottom are the oldest
Faster water flow = more/heavier pieces moved
Water slows/stops = deposition in flat layers
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(Activity #5 – Step 2)
Original Horizontality- rocks are deposited in horizontal layers
Superposition – rocks at the bottom are the oldest
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Some important principles: “Relative Dating”
Inclusion – younger rocks may incorporate pieces of older rocks
Cross-cutting relationships – older rocks may be cut by younger rocks or features (examples: intrusions of magma, faults)
older
older
younger
older
older
younger
younger
older
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Faults- break in rock layers, motion on either side
The fault is YOUNGER than the rocks – the rocks had to be there for the fault to cut through.
It cross-cuts the layers
(Activity #6) Siccar Point, Scotland James Hutton recognized its significance
Greywackes – base layers at Siccar point. Greywackes are sed layers formed in the ocean near fast rising mountains. They contain poorly sorted, angular grains of all types, the result of streams being uplifted and then downcutting rapidly, carrying all manner of material downstream and dumping it in the ocean.
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Faults- break in rock layers, motion on either side
A
B
C
Handout #7
Look at this stunning photo of folded rock layers in France.
a. What are TWO geological events you can see documented? (Hint: these are one-word answers)
b. Which layer is oldest, and which is youngest (A,B, C)?
Oldest =
Youngest =
Turn in participation to a TA or Preceptor on your way out (IS YOUR NAME ON IT?)! Remember, there are no make ups on participation. These are easy points – come to class, participate, earn max. points!