Across

2. The study of the movement of a planet's crustal plates.

5. The layer of loose, rocky material covering bedrock.

9. The process where a liquid turns into a gas.

10. Long-term weather patterns of a region.

11. Ground that remains frozen for two or more years.

12. A planet's magnetic shield against solar wind.

14. A dark, fine-grained volcanic rock common on Mars.

17. Relating to the effect of gases trapping heat in an atmosphere.

18. Matter that settles to the bottom of a liquid.

19. The gas essential for animal respiration.

20. The solid rock underlying surface materials.

21. The wearing away of land by natural forces.

Down

1. The eruption of molten rock onto a planet's surface.

3. A large group of rock-forming minerals.

4. A molecule (O₃) that forms a layer to block UV radiation.

6. The breaking down of rocks by wind and water.

7. The process where water vapor becomes liquid.

8. The gaseous envelope surrounding a planet.

13. The force exerted by the weight of the air.

15. An underground layer of water-bearing rock.

16. Fine particles suspended in gas, used to alter atmospheric properties.