Across
- 4. sun
- 5. not essential
- 6. conserve resources
- 8. not man-made
- 10. gasoline
- 12. powering machines, transportation, or heating homes
- 14. force, pressure
- 15. important resources
- 17. cannot be replaced once it is used up
- 18. minimizing consumption
- 20. long-lasting
Down
- 1. ancient energy sources
- 2. moving water
- 3. extract new resources
- 7. limited supply
- 8. essential
- 9. usable things
- 11. plants, animals, and microorganisms
- 13. earth's internal heat
- 16. sources of energy uses to generate power
- 19. turbines