Geology 12 - Historical Geology
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Stratigraphic Principles

Reading: Chapter 1, 2 & 4

• We only need a bit of Chapter 1 (but of course you are welcome to read it all): the short section on Catastrophic v Uniform Views of Change (p. 12-13).
• Skip over to Chapter 2. We are not so interested in the historical development of the science, so you can skim the historical parts, but do look for the two key concepts: catastrophism and uniformitarianism. You also need to note the definitions and applications of the stratigraphic principles in question #3 below. You can skip the section on natural selection (p. 20-21).
• In Chapter 4, read the section on unconformities (p.82-82) and corollaries to superposition (p. 74).

If you do not have the textbook, use these Web sites to answer the questions:

http://www.cas.muohio.edu/glg/museum/students/conceptsingeology/thebigpicture/sixmainprinciplesofrelativetime.html

The six principles of stratigraphy

http://en.wikipedia.org/wiki/Uniformitarianism

A history of the concept of uniformitarianism and how it contrasts with the modern concept of actualism.

http://evolution.berkeley.edu/evosite/history/uniformitar.shtml

Read all three pages to understand the difference between Lyell's brand of uniformitarianism and the way geologists understand the concept today.

Background

Terms you should know:

Key Concepts and Questions:

1. How fast do geologic events occur?

We will do an exercise in class to help illustrate this.

Summarize here what you learned about geologic rates.

2. What does uniformitarianism - the essential paradigm of geology - mean?

a. Catastrophism - the initial assumption in studying the Earth.

What does catastrophism assume about how the Earth formed and developed?

 

 

Find a couple examples of early theories of the Earth that rely on catastrophist explanations.

 

 

b. Uniformitarianism

Read about Lyell's version of uniformitarianism. How does our modern understanding of uniformitarianism (Levin calls it actualism) differ from Lyell's uniformitarianism?

 

 

 

What evidence supports our uniformitarian view of the world?

 

 

 

3. How do we put geologic events in the proper order?

A. Principles of stratigraphy: for each, define and draw a sketch (p. 19-20, 24, 74)

Original horizontality:

 

 

Superposition:

 

 

Original lateral continuity:

 

 

Cross-cutting relationships:

 

 

Included fragments (inclusions):

 

 

Fossil succession:

 

 

Assessment

1. Rates

You should be able to:

• contrast geologic rates with more familiar rates
• describe how geologic processes can create enormous amounts of change even though they often operate slowly

2. Uniformitarianism

You should be able to:

• contrast catastrophic and uniform explanations of Earth history
• explain how uniformitarianism informs geologic explanations
• cite evidence for uniformitarianism as an organizing concept of geology

3. Stratigraphic principles

You should be able to :

• define and illustrate each principle
• apply the principles to tell geologic histories