from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The region of the atmosphere from 30 to 190 kilometers (20 to 120 miles) above the earth's surface, in which photochemical reactions initiated by solar radiation occur.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. the region of the Earth's atmosphere (from 20 to 120 miles above the surface) in which photochemical reactions take place
chemo- + -sphere (Wiktionary)