Across
- 2. dying out of a species
- 4. living things in the environment
- 6. layer of air surrounding the earth
- 8. the gas we can't live without
- 9. the most important gas in the atmosphere
- 10. the blue planet
Down
- 1. a linear sequence of organisms through which nutrients and energy pass as one organism eats another
- 3. the erosion of the top layer of dirt known as topsoil
- 5. the introduction of harmful materials into the environment
- 7. cutting down of trees on a large scale