296-202 Physical Geology
Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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What is Geology?
The sciences that set the general principles for all the other
- Mathematics - "The Rules"
- Physics - "The Board
- Chemistry - "The Pieces"
The sciences that describe the great systems that make up the
- Astronomy - Stars and Galaxies
- Geology - Planets
- Biology - Life
- Psychology - The Mind
- Sociology - Social Communities
Sciences that examine some smaller, more manageable part of
the Basic or Megasystem Sciences
Geology Relates to all other Sciences
- Historical Geology
- Economic Geology
- Structural Geology
Who Geoscientists Are:
- About 30,000 in the U.S.
- Globally, in rich and poor countries, about one per $50
- Mostly male but changing rapidly (now about 25% female in
- Still less than 10% minority in U.S. (moving up slowly)
Where Geologists Work
- 40 % Private Sector
- 30 % Academic
- 30 % Government
What Geologists Do:
Locate Geologic Resources
Geologic Hazard Mitigation
- Geological and Mining Engineering
- Site Study
- Land-Use Planning
- Environmental Impact
- Ground Water and Waste Management
Basic Research (Furnishes fundamental knowledge for the
Some Unique Aspects of Geology
Importance of Relationships
Importance of Time
Some Geologic Rates
- Cutting of Grand Canyon
- 2 km/3 m.y. = 1 cm/15 yr
- Uplift of Alps
- 5 km/10 m.y. = 1 cm/20 yr.
- Opening of Atlantic
- 5000 km/180 m.y. = 2.8 cm/yr.
- Uplift of White Mtns. (N.H.) Granites
- 8 km/150 m.y. = 1 cm/190 yr.
- Movement of San Andreas Fault
- 5 cm/yr = 7 m/140 yr.
- Growth of Mt. St. Helens
- 3 km/30,000 yr = 10 cm/yr.
- Deposition of Niagara Dolomite
- 100 m/ 1 m.y.? = 1 cm/100 yr.
At 1 Second = 1 Year:
- 35 minutes to birth of Christ
- 1 hour+ to pyramids
- 3 hours to retreat of glaciers from Wisconsin
- 12 days = 1 million years
- 2 years to extinction of dinosaurs
- 14 years to age of Niagara Escarpment
- 31 years = 1 billion years
Distinctive Problems of Evidence
- Slow Rates
- Rare Events
- Destruction of Evidence
Reliance on Inference and Deduction
Intrinsically "Unsolvable" Problems
Ancient Ocean Basins
Scientific Principles in Geology
- Parsimony (K.I.S.S.)
Using these, plus observation, we establish facts about Earth
A Whodunit? Last night one of Green Bay's premier beer
can collections was stolen. The only clues are tracks in the snow.
We know the last person leaving the scene was the thief. Below:
the evidence and the suspects
|The Butler walks to work
Handyman rides a bike
The Cook rides a motorcycle
The Maid drives a car
The Nephew has a seeing-eye dog
If you ever watch mysteries nowadays, you know the butler never
does it any more. But if one of the dog's footprints had not
chanced to overlap the butler's, we would not be able to tell
which of the two went last. That often happens in geology - you
can't always tell which of two events happened last, and often
having the critical evidence is a matter of chance.
Contacts between rock bodies are where we find the critical
information about time relationships. Below is a hypothetical
view of a cliff. The colors and patterns are commonly used in
geology. The green lined beds are shale, the blue brickwork
denotes limestone, and the yellow stippled rocks are sandstone.
The red is an intrusion and the gray is a fault.
The order in which the rock layers formed is obvious: those on
the bottom formed first. The intrusion has to post-date at least
the uppermost layer it intrudes. Intrusions often alter or bake
the adjacent rocks (dark tones) and include chunks of them.
The fault shown here is actually more realistic than the
simple lines shown in most illustrations. Generally faults are
zones of fractured and crushed rock rather than simple clean
planes. Now how do the rocks left of the fault relate to those on
the right? We can't tell. Nowhere right of the fault do we find
sandstone bounded above and below by shale. So we'll have to go
elsewhere to find out. The logical way to sort out data gathered
at widely separated localities is to plot it on a map. Obviously
the fault is later than all the rocks it cuts.
What about the fault and the intrusion? Here we'd have to get
up close to the fault and look. If the intrusion baked the rocks
in the fault zone or cut across parts of the fault, we'd conclude
the intrusion was later. If there were bits of the intrusive rock
included in the fault zone, we'd conclude the fault was later.
Continuity of Cause and Effect
- Apply Cause and Effect to Future - Prediction
- Apply Cause and Effect to Present - Technology
- Apply Cause and Effect to Past - Uniformitarianism
Uniformitarianism does not mean:
- Catastrophes never occur
- Physical Conditions on Earth never Change
- Earth has always been the same
- Physical processes always occur at the same rate or
- Laws of Physics have always been the same
Uniformitarianism does mean:
Using our knowledge of physical laws:
- We can test whether catastrophes have occurred (they have,
but rarely. Real catastrophes leave absolutely
unmistakeable physical evidence.)
- We can test whether physical conditions on earth have
changed, and if so, how (ice ages, warm periods, high or
low sea level, etc.)
- We can test whether physical laws themselves have changed
in time, or elsewhere in the universe (despite intensive
searches, there is no evidence for any changes.)
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Last Update 2/3/1997