St Petersburg College the Snowball Earth Hypothesis DiscussionSchool

ST PETERSBURG COLLEGE

Question Description

• Required: Snowball Earth, Paul Hoffman and Daniel Schrag, Scientific American, Jan. 2000.
• Optional: A Neoproterozoic Snowball Earth. Hoffman, P., Kaufman, A., Halverson, G. and Schrag, D. Science. August 1998.
• Optional: The BBC Horizon Documentary Snowball Earth: How the Planet Froze and Lived to Tell is available on YouTube

Assignment:

1. The roots of the snowball earth hypothesis go back almost 100 years. What were the earliest clues that the earth may have been completely covered in ice at some time in the past? (15 points)
2. Carbon dioxide (CO2) is often called a greenhouse gas . What effect would decreased CO2 levels in the atmosphere have on the climate? Explain (15 points)
3. A portion of all solar radiation (heat from the sun) is absorbed by the earth and a portion is reflected back out into space. The amount of solar radiation that a material reflects back out to space is called the albedo . Do sea-ice and continental glaciers have a higher or lower albedo compared to sea-water and land vegetation? What effect would expanding glaciers have on the amount of solar radiation that is absorbed by the earth? Explain. (15 points)
4. According to the Snowball Earth hypothesis, what caused the earth to become completely frozen over (global glaciation)? Specifically, describe the plate-tectonic conditions, and the chemical and physical mechanisms that drove the earth into a deep-freeze. (15 points)
5. Previous to the work of Hoffman and Schrag, many scientists thought that the earth would not recover (warm) from a snowball earth, if it ever happened. Describe Hoffman and Schrag s hypothesis of how the earth would have reversed the deep freeze and entered a global hothouse state. (15 points)
6. Paleontologists have observed that the period directly following the neo-proterozoic is characterized by a huge expansion and diversification of life. This significant evolutionary interval is oft referred to as the Cambrian Explosion . According to the authors how did the snowball earth significantly effect, and perhaps even catalyze, the Cambrian Explosion? (15 points)
7. What do you think about the Snowball Earth Hypothesis? Is it a reasonable hypothesis in light of the evidence uncovered so far? What could be an alternative hypothesis to explain the existence of so many glacial deposits found directly underneath (and immediately before in time) tropical warm ocean deposits? (10 points)

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