1. Have you thoroughly read chapter 2?

2. How long ago did the Cambrian explosion take place?

3. Describe the Miller-Urey experiment.

4. Name an example of artificial selection (other than Heike crabs).

5. Briefly describe the structure of DNA.

6. When did one-celled plants first evolve on our planet?

7. Why does Sagan say the "sky is made by life"?

8. Why do Heiki crabs look like samurai warriors?

9. Viroids, the smallest living thing known, are composed of less than __________ atoms.

10. Name a couple of lifeforms Sagan speculates could possibly inhabit Jupiter.