Tags Science
Startribune posted a curious small article named Why is the sky blue? Facts you should know. I'll reproduce the questions and the answers:
  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?
  11. Extra credit: What makes the seasons change?

The answers are:

1. About 71 percent of the earth's surface is covered by water.

2. The single cells in the brain communicate through electrical and chemical signals.

3. No. Dinosaurs went extinct at the end of the Cretaceous period, 65 million years ago. Modern humans did not appear until around 200,000 years ago.

4. Darwin's theory of species origination says that natural selection chooses organisms that possess variable and heritable traits and that are best suited for their environments.

5. A year, 365 days, is the time it takes for the earth to travel around the sun. A day, 24 hours, is the time it takes for the earth to spin around once on its axis.

6. Solar radiation sunlight is scattered across the atmosphere by a process called diffused sky radiation. The sky is blue because much more short-wave radiation -- blue light -- is scattered across the sky than long-wave radiation -- red light.

7. Rainbows can be seen when there are water droplets in the air and the sun is shining. Sunlight, which contains all colors, is refracted, or bent, off the droplets at different angles, splitting into its different colors of red, yellow, blue, etc.

8. Influenza viruses and others continually change over time, usually by mutation. This change enables the virus to evade the immune system of its host so that people are susceptible to influenza virus infection throughout their lives. Bacteria mutate in the same way and can also become resistant if overtreated with antibiotics.

9. About 3.8 billion years; they're bacteria-like organisms.

10. Adding salt to snow or ice increases the number of molecules on the ground surface and makes it harder for the water to freeze. Salt can lower freezing temperatures on sidewalks to 15 degrees from 32 degrees.

Extra credit: Seasons occur because the earth is tilted at an angle of 23.5 degrees. At certain times of year the top half of the earth leans to the sun and therefore gets more sun and has summer. When that same half of the earth leans away from the sun it gets less light and has winter.


Most of these are trivial. I wasn't sure about 6, 9, 8 and the Extra, had no idea about 10. In fact, the answer to 10 seems a bit strange to me - what does "increases the number of molecules on the ground surface" mean exactly. After some web research it appears that the answer is simple: salty water has a lower freezing temperature. That's about it...