Devonian Transformation

Kathryn Hoppe
Green River Community College
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Students use the web to examine the biologic, geologic, atmospheric, and climatologically changes that occur with the evolution of land plants. This write up is a summary of web-based readings which the students need to complete before an in-class discssion.

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This exercise is used in a 200 level class "Evolution of the Earth." The prerequisit for this class is Physical Geology (Geology 101). There are typically 15 to 20 students registered for the class

Skills and concepts that students must have mastered

Geologic Time scale
Basic evolutionary theory
Navigating the World Wide Web
Working in groups and presenting their conclusions in an in class discussion format.

How the activity is situated in the course

This is part of a sequence of exercises on the evolution of life in the Phanerozic.


Content/concepts goals for this activity

Students should understand the link between the evolution of land plants and:

Weathering Rate on Land
Nutrient Flux to the Oceans
Burial of Organic Matter
CO2 levels in the Atmosphere and corresponding climatic changes.

Higher order thinking skills goals for this activity

Students should evaluate the link between the lithosphere, biosphere, and atmosphere.

Other skills goals for this activity

searching WWW, working in groups and oral presentation.

Description of the activity/assignment

To complete this assignement student have to work in groups to answer a series of questions on the evolution of land plants. They need to combine material previously covered in lecture and information from the WWW to determine how the evolution of land plants changed the lithosphere, atmophere, and biosphere.

After completing the attached exercise the students participate in a guided discussion. There are several way to divide students up into groups.

Different groups are asked to summarize: the link between the spread of land plants and

1) atmospheric carbon levels and climatic conditions,

2) organic carbon and dissolved oxygen levels in the ocean

3) the abundance of corals and other marine animals: shallow vs. deep ocean

4) Erosion rates on land and rates of organic matter burial in the oceans.

5) General patterns in diversity and biomass of marine and terrestrial fauna

Then each group is asked to discuss how the aspect they considered about the Devonian Extinction fits into and differs from conditions we see in the modern carbon cycle.

Determining whether students have met the goals

Students are evaluated based on a brief oral presentation by each group and by the summary answers written down by each individual students.

A variation: Students could be asked to draw a concept sketch of how the carbon cycle changed in the late Devonian and compare this with a concept sketch of how the modern carbon cycle is changing.

Aspects they should consider =

Devonian-biomass of living plants (e.g., Evolution of forest ecosystems in the Devonian vs. Deforestation)

Organic carbon burial rates, erosion rates, nutrient flux to oceans and shallow marine turbidity levels

Carbon Dioxide levels and oxygen levels in the ocean, atmosphere

Effects of changing terrestrial biomass levels on climate (both temperature and rainfall patterns)

Diversity of marine and terrestrial fauna

More information about assessment tools and techniques.

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