Atmospheric carbon dioxide is the primary source of carbon in life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by photosynthetic organisms and geological phenomena.
At about 55 km, the mesosphere begins. In the mesosphere, the temperature decreases with height again, because there is very little ozone to warm up the air. Finally, the mesopause divides the mesosphere from the thermosphere, which is the section of the atmosphere higher than 90 km. In this region, the temperature increases again. This time, it is molecular oxygen (O2) that causes the temperature increase.
Therefore, the air pressure is lower. Air temperature changes as you go higher above the earth. Since the surface of the earth heats the air above it, the air is warmer near the ground. Air pressure on the earth's surface also changes. Changes in temperature cause changes in air pressure. As the air near the surface of the earth becomes warmer, the particles becomes warmer, the the particles of the air move farther apart. The air becomes lighter and rises. The lighter air pushes down on the surface of the earth with less pressure.