To cope, we must rely on preventive measures and, in some cases, life-support equipment. By understanding the characteristics of the atmosphere, aircrews are better prepared for the physiological changes that occur with increasing altitudes. The atmosphere is like an ocean of air that surrounds the surface of the Earth. It is a mixture of water and gases. The atmosphere extends from the surface of the Earth to about 1,200 miles in space.
Gravity holds the atmosphere in place.
Without the atmosphere, the Earth would be as barren as the moon. The atmosphere consists of several concentric layers, each displaying its own unique characteristics. Each layer is known as a sphere. Thermal variances within the atmosphere help define these spheres, offering aviation personnel an insight into atmospheric conditions within each area. Between each of the spheres is an imaginary boundary, known as a pause.