Dropping More Science

The Minneapolis Star-Tribune, of all places, has compiled ten replies to the question, "What is one science question every high school graduate should be able to answer?"

Try them; they're good and the explanatory answers are at the bottom of the original article:

1. What percentage of the earth is covered by water?
2. What sorts of signals does the brain use to communicate sensations, thoughts and actions?
3. Did dinosaurs and humans ever exist at the same time?
4. What is Darwin's theory of the origin of species?
5. Why does a year consist of 365 days, and a day of 24 hours?
6. Why is the sky blue?
7. What causes a rainbow?
8. What is it that makes diseases caused by viruses and bacteria hard to treat?
9. How old are the oldest fossils on earth?
10. Why do we put salt on sidewalks when it snows?
Extra credit: What makes the seasons change?