1. In the class notes we make use of the Drake equation as providing a statistical estimate of the number of civilizations that might exist in our Galaxy and are capable of communication. Recently, however, some scientists have argued that the Drake equation is an inaccurate description. This new theory is known as the "Rare Earth Theory" (by Ward and Brownless). Do some research on this new theory and identify what the key components of this theory are that suggests planets like the Earth are much rarer than we think they are.

2. Explain about how various kinds of systematic variations in the Earth's orbit about the sun are thought to be the best explanation for periodic ice ages on the Earth.

3. Research and describe the Gliese 581 planetary system which has recently been detected. How does this planetary system differ from other exosolar systems detected to date and why are astronomers relatively excited by this system? Go to exoplanets.org for a comprehensive view of all new planetary systems discovered to date.

4. A dramatic new view of the geologic history of the Earth has arisen in the last few years. This view is quite controversial and is known as "Snowball Earth." Summarize what this theory is and what is some of the evidence for and against this hypothesis.

5. Do some research on hydrothermal vents and their associated biological communities. Provide an argument that it is this environment that is most responsible for the existence of life on Earth.