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Across 4. the process of eroding or being eroded by wind, water, or other natural agents. 7. a colorless unstable toxic gas with a pungent odor and powerful oxidizing properties, formed from oxygen by electrical discharges or ultraviolet light. It differs from normal oxygen (O2) in having three atoms in its molecule (O3). 9. the surroundings or conditions in which a person, animal, or plant lives or operates. 10. A forest of cone-bearing trees 11. A scientist who specializes in the study of plants 12. the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a byproduct.

Down 1. the trapping of the sun's warmth in a planet's lower atmosphere due to the greater transparency of the atmosphere to visible radiation from the sun than to infrared radiation emitted from the planet's surface. 2. a person, company, or country that makes, grows, or supplies goods or commodities for sale. 3. the natural home or environment of an animal, plant, or other organism. 5. the state or process of a species, family, or larger group being or becoming extinct. 6. the envelope of gases surrounding the earth or another planet. 8. The study of man.