The Earth is surrounded by the atmosphere, a blanket of gases that has no definite outer edge. Over 80 percent of the gases in the atmosphere are held by gravity within 12.4 mi. (20 km) of the Earth's surface. The physical ...

  • Loading...
locked icon

Sign in to access this content

Get a 30 day FREE TRIAL

  • Watch videos from a variety of sources bringing classroom topics to life
  • Read modern, diverse business cases
  • Explore hundreds of books and reference titles