Chapter 8

1. this planet is believed to have once had a magnetic field that disappeared when the planet's iron core cooled
2. special water scientist look at in the oceans and in comets to see if the proportions match
3. shrinks under its own weak gravity
6. clumping smaller particles into larger masses
8. protects us from UV
10. every chemical element that made the planets, stars, oceans, and organisms
11. the north poles movement is
14. clear so sun can penetrate
15. distance from the sun allows for liquid ____
16. the star's core will eventually collapse in an explosion known as
17. what type of energy heated earth
19. this is why stars shine
22. like a spinning skater that brings their arms in
23. has more stars than grains of sand on all beaches

1. moves 1 1/2 inches away from the earth every year
4. had a beginning
5. massive spheres of incandescent gas
7. how stars and planets were formed
9. occurred 15 billion years ago
12. gives information about the conditions in which the solid planets formed
13. experiment in 1953
18. when earth was liquid rock what type of elements sank toward earth's center
20. radioactive elements found in a meteorite that decays at a particular rate can be used to calculate the meteorite's
21. earth irons core creates a magnetic field which protects the planet from