Across
- 2. substances released into the air.
- 4. fuels fuel formed from ancient organisms.
- 5. fixation converting nitrogen gas into usable forms.
- 9. the layer of gases around earth.
- 10. necessary.
- 13. converting nitrogen into nitrates in soil.
- 14. burning.
- 15. work or act together.
- 17. a gas essential for life.
- 18. development of cities.
Down
- 1. plants making food using sunlight.
- 3. growing crops and raising animals.
- 6. control or manage.
- 7. water falling from clouds.
- 8. breaking down dead matter.
- 11. related to industry and manufacturing.
- 12. using resources without depleting them.
- 16. releasing energy from food.