Earth Day

5. branch of biology that deals with the relations of organisms to one another and to their physical surroundings.
7. to or derived from living matter.
9. being capable of being renewed
13. something in its original or existing state
14. production and discharge of something, especially gas or radiation
16. organic material used as a plant fertilizer
19. natural home or environment of an animal, plant, or other organism
20. as paper, cans, and bottles, that is left lying in an open or public place

1. (water, air, or a place) with harmful or poisonous substances
2. to or determined by the sun
3. something, especially an environmentally or culturally important place from harm or destruction
4. discarded objects in such a way as to create a product of higher quality or value than the original
6. to be maintained at a certain rate or level
8. colorless unstable toxic gas
10. a species,family, or other group of animals or plants having no living members; no longer in existence
11. layer of gases that surround the planet
12. surroundings or conditions in which a person, animal, or plant lives or operates
15. biological community of interacting organisms and their physical environment
17. again
18. place to dispose of refuse and other waste material by burying it and covering it over with soil, especially as a method of filling in or extending usable land