Geology 12 - Historical Geology
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Archean and Proterozoic History

Reading: Chapter 8

This is a hard chapter to read. There's a lot of names and regional detail that we are not going to deal with. Try to filter out as much as you can and look for the big ideas. Here's a page-by-page guide to help you through.

p. 152-158: There's a lot of detail here that we don't need. The take-home message: there are Cryptozoic rocks in the center of North America that form a few distinct provinces - see Fig. 8.8 (Geologic provinces of the core of North America...) and Fig. 8.10 (Hypothetical scenario for the assembly of North America...). The provinces seem to be chunks of crust that assembled by collisions over time. We want to concentrate on the processes that form these rocks (see questions below).

p. 158-163: you already read this section earlier in the semester.

p. 164 and fig. 8.9 (Evolution of greenstone belts) on p. 157: this is what you need to know about Archean processes.

p. 164-168: Most of what you need to know about Proterozoic rocks is here.

p. 168-172: evidence for the origin of oxygen in the atmosphere

p. 172-175: evidence of glaciation and Snowball Earth

Terms you should know:

Key Concepts and Questions:

1. How was plate tectonics different in the Archean?

How did greenstone belts form? What modern plate setting are they most like?

 

 

How did gneiss belts form? What modern plate setting are they most like?

 

 

What is the relationship between the greenstone and gneiss belts?

 

 

How was Archean plate tectonics different than modern plate tectonics?

 

 

2. How are Archean rocks different than Proterozoic rocks?

What kind of sedimentary rocks are found in the Proterozoic? What kind of plate setting are these rocks associated with?

 

 

 

3. What kind of plate tectonic events happened in the Proterozoic?

What kind of rocks and geologic structures are found in the Keweenawan group? What kind of tectonic basin/plate boundary are these rocks associated with?

 

 

4. How did the atmosphere evolve through the Cryptozoic? What is the evidence?

How do banded iron formations provide evidence of changes in the atmosphere?

 

 

 

5. Why is Proterozoic glaciation important?

What is the evidence of glaciation throughout the Proterozoic?

 

What conditions allowed massive glaciation even at low latitude near the equator?

 

Why is this important to the history of life?

 

 

Assessment

1. Archean-Proterozoic

You should be able to:

• describe the differences between Archean and Proterozoic rocks, and what they tell us about changes in plate tectonic processes
• use what you know about tectonic stratigraphy and the geologic features of plate boundaries to interpret the plate settings of Archean or Proterozoic rocks.

2. Atmosphere and climate

You should be able to:

• describe why BIFs are puzzling, and how they may have formed
• discuss the evidence for the development of oxygen in the atmosphere
• discuss the significance of Proterozoic galciation - how it happened, why we care.