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.
Through this labyrinth of blood vessels, now called veins, the hemoglobin returns carbon dioxide through the heart and to the lungs. Carbon dioxide is released back out as you exhale, and the process starts all over again. Everywhere on earth, oxygen makes up 20.96% of the gas in air (almost all the rest is nitrogen). The atmospheric pressure helps determine just how dense this air is, and therefore what concentration of oxygen the air contains.