Did you finish high school?

Then according to the world's leading scientists, teachers and others, you should know the answers to these questions:

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

Answers here. I knew the correct answers to 6.