I would like to look at one more aspect of the "earth is special" argument. Our atmosphere is unique within the solar system. Mercury has no atmosphere. Venus's atmosphere is a mix of sulfuric acid, carbon dioxide, and water vapor. Jupiter's is mostly ammonia and methane. And the earth's -- 80% nitrogen, 20% oxygen. Why should the earth be so different? It seems each planet is in some ways distinct from all the others and that the atmosphere of a planet is a result of its position in the solar system and its geologic and, in the case of Earth, organic evolution.

 

I. Atmospheres in the solar system

A. The sun and planets

 

 

B. What might be expected

 

II. Earth's origins and its primordial atmosphere

A. Solar ignitions

 

II.B An aside on tendencies in natural systems (EXTREMELY IMPORTANT)

1. Potential energy decrease

 

2. Entropy increase

 

3. Temperature -- effects and causes

 

4. Implications for atmospheres

 

C. Secondary atmospheres

 

III. An evolving planet

A. Beginnings of life

   

B. Aerobic and anaerobic bacteria

 

C. Atmospheric threshold and the Cambrian explosion

 

D. Describing the modern atmosphere

 

IV. The atmosphere as greenhouse

A. Molecules and energy absorption

 

B. The earth's atmosphere as window and wall to radiation

1. UV and ozone

 

2. Visible light

 

3. Infra-red, CO2 and H2O

Objectives:

1. Describe the different atmospheres that are found in the solar system.

2. Discuss the earth's expected primordial atmosphere and why we might not expect to find it today.

3. Give examples of how decreasing potential energy and increasing entropy affect the outcome of changes in natural systems.

4. Explain how entropy increase would favor the escape of atmospheric gases from earth's gravitational field and the effect of temperature on that tendency.

5. Discuss sources of earth's secondary and tertiary atmospheres.

6. Explain the ability of the atmosphere to prevent penetration of UV light to the earth's surface.

7. Discuss the effect of carbon dioxide and water vapor on the release of energy from the earth as radiation.

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