Geology 12 - Historical Geology
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Earth Systems; Stratigraphic Principles

Reading: Chapter 1

Some parts of this chapter we'll be dealing with in detail later, so you just need to skim those sections. Other parts we need in detail.

These sections you can skip if you already have a good background in them (page #s are second edition/first edition). If your previous Geology course was Earth Science or Natural Disasters, you should read these sections:

• Nature and Origin of Rocks (p.6-8/p.5-8)
• Radioactive decay, Geologic time scale, Imaging Earth Below, Plate Tectonics (p.12-18/p.12-20)

Everyone should skim these sections:

• Exploring Earth System (p.3-4/p.2)
• Water Cycle (p.18-20/20-22)

Everyone should read these sections carefully:

• Uniformitarianism (p.4-6/p.3-5)
• Steno's three laws, Rock cycle, Fossil dating (p.9-11/p.9-12)
• Directional Change, Episodic Change (p.20-24/p.22-26)

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

http://www.mhhe.com/earthsci/geology/mcconnell/gti/relative.htm

Definitions and illustrations of the principles of stratigraphy. Be sure to step through all the principles. Stop when you reach the page on the Geologic Time Scale.

http://etext.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv4-56

An incredibly detailed history of the concepts of uniformitarianism and catastrophism. Read up to the first horizontal bar; the rest is optional.

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:

The textbook is not necessarily set up in the same structure as the Reading Guides. You will probably have to pull concepts from different parts of the chapter to answer the questions below. Read the questions here BEFORE you start reading the chapter, then keep the Reading Guide beside you as you go through the chapter. Be sure to record important ideas under the appropriate question below as you read.

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?

 

 

 

b. Uniformitarianism

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

 

 

 

What evidence supports our uniformitarian view of the world?

 

 

 

Did past events all occur "uniformly" - that is, are all earth events gradual? Can they all be reversed?

 

 

 

 

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

A. Principles of stratigraphy: for each, define and draw a sketch.

Original horizontality:

 

 

Superposition:

 

 

Original lateral continuity:

 

 

Intrusive (Cross-cutting) relationships:

 

 

Components:

 

 

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