Mesosphere

The mesosphere is the middle layer in the atmosphere (hence, mesosphere). There are two key points about the mesosphere. First, temperature in the mesosphere decreases with height. At the top of the mesosphere, air temperature reaches its coldest value, around -90 degrees Celsius (or -130 degrees Fahrenheit). The second point is that the air is extremely thin at this level. Over 99.9 percent of the atmosphere's mass lies below the mesosphere. However, the proportion of nitrogen and oxygen at these levels is about the same as at sea level.

The mesosphere is bounded above by the mesopause. The average height of the mesopause is about 85 km (53 miles), where the atmosphere again becomes isothermal. This is around the 0.005 mb (0.0005 kPa) pressure level. Above the mesosphere is the thermosphere.