The Navajo are the second largest tribe in the U.S. and they have the largest reservation stretching across Colorado, Utah, New Mexico and Arizona with over 25,000 square miles. They were also among the largest group of Indians to migrate to Los Angeles in the 1950s and 60s.
The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km (31 mi) to more than 1,000 km (620 mi).
The troposphere is the lowest layer of the atmosphere and contains 75 per cent of all its gases. Above is the stratosphere, which includes the ozone layer. Higher still is the thin air of the mesosphere, where meteors burn up. The thermosphere contains an electrically charged layer that radio waves bounce off.