Across
- 4. a source
- 6. salted water
- 8. DNA and RNA are called
- 11. a toxic colorless gas surrounding the earth
- 12. Water on earth
- 13. smoke mixed with fog
- 15. emission of energy as electromagnetic waves
- 16. 21% of atmosphere
- 17. fourth stage in water cycle
- 18. air on the earth's surface
Down
- 1. Green plants and animals are also known as
- 2. most important gaseous cycle
- 3. process of rotting
- 5. used in nitrification
- 7. compound of hydrogen and carbon
- 9. a rigid external covering for some animals
- 10. living organisms on earth from the _ component
- 14. glass building which usually has plants