advanced practice nurse a registered nurse having education beyond the basic nursing education and certified by a nationally recognized professional organization in a nursing specialty, or meeting other criteria established by a Board of Nursing.
Quick Answer. The air that makes up Earth's atmosphere contains 20.9 percent oxygen. This is true up to about 70,000 feet above sea level. However, above 10,000 feet, the atmosphere becomes too thin to support human life, even though its proportions do not change much. Continue Reading.
At low elevations, the pressure is greater, since the molecules of air are compressed from the weight of the air above them. However, at higher elevations, there's less pressure and the molecules are more dispersed. The percentage of oxygen in the air at sea level is the same at high altitudes -- roughly 21 percent. But because the air molecules are more dispersed, each breath delivers less oxygen to the body. When you take a breath at 12,000 feet (3,657.6 m), you're breathing in 40 percent less oxygen than at sea level.