296-202 Physical Geology

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

What is Geology?

Basic Sciences

The sciences that set the general principles for all the other sciences

Megasystem Sciences

The sciences that describe the great systems that make up the Universe


Specialty Sciences

Sciences that examine some smaller, more manageable part of the Basic or Megasystem Sciences

Geology Relates to all other Sciences

  • Geophysics
  • Seismology
  • Historical Geology
  • Economic Geology
  • Structural Geology
  • Hydrology
  • Oceanography
  • Geomorphology
  • Mineralogy
  • Petrology
  • Geochemistry
  • Planetary Geology
  • Paleontology
  • Paleo-
    • ecology
    • botany
    • climatology
    • ....etc.

Who Geoscientists Are:

Where Geologists Work

What Geologists Do:

Locate Geologic Resources

Geologic Hazard Mitigation

Environmental Protection

Basic Research (Furnishes fundamental knowledge for the applications)

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:

Distinctive Problems of Evidence

Reliance on Inference and Deduction

Intrinsically "Unsolvable" Problems

Ancient Landscapes

Mass Extinctions

Ancient Ocean Basins

Scientific Principles in Geology

Using these, plus observation, we establish facts about Earth Processes


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

The 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

Uniformitarianism does not mean:

Uniformitarianism does mean:
Using our knowledge of physical laws:

Return to Overheads Index

:Return to Professor Dutch's home page

Last Update 2/3/1997