When the Earth was first formed, its primitive atmosphere was made up of hydrogen and helium, just like our sun.
Scientists hypothesize that gases released from volcanic eruptions, primarily carbon dioxide, sulfur dioxide, water vapor, and nitrogen probably made up the early atmosphere. Early volcanic activity and meteorite impacts can inject large quantities of dust and gases into the early atmosphere. The dust acts as seeds for clouds.
The amount of oxygen in the atmosphere increased when early photosynthetic life – cyanobacteria (blue-green algae) – consumed carbon dioxide and generated oxygen.
Today’s Earth’s atmosphere is 78% nitrogen, 21% oxygen, and 1% trace gases (carbon dioxide, argon, hydrogen, etc).
Troposphere: Lowest layer of the atmosphere where temperature decreases with altitude.
Tropopause: Area between the troposphere and stratosphere where the temperature stops decreasing.
Stratosphere: Clear, dry layer above the tropopause. Upper part of the stratosphere warms steadily because of the
ozone layer. Ozone absorbs ultraviolet rays and releases this energy in the form of heat.
Stratopause: Area between stratosphere and mesosphere where the temperature stops increasing.
Mesosphere: Area above the stratosphere where temperatures decrease as you move up in altitude.
Mesopause: Area between the mesosphere and thermosphere where the temperature stops decreasing.
Thermosphere: Atmosphere is very thin, but receives intense solar radiation. A portion of the thermosphere is called the ionosphere, where the sun’s radiation knocks off electrons in the gases and causes them to form auroras.

Our atmosphere is stable because of a delicate balance of gases moving between parts of the Earth system: atmosphere, geosphere, hydrosphere, and biosphere.
The carbon dioxide content of the atmosphere has increased due to human activities, primarily the burning of fossil fuels: coal, gasoline, and natural gas.
Energy from the sun heats the Earth’s atmosphere and surface.
Heat moves through the atmosphere in three different ways: conduction, convection and radiation.
Conduction: Transfer of heat energy through collisions of the molecules of a substance. An example is air touching the warm ground.
Convection: Transfer of heat energy through motion of liquid or gas caused by differences in density.
Radiation: Transfer of energy through space in the form of electromagnetic waves. Energy from the sun radiates through space to heat the atmosphere and Earth’s surface by conduction & convection
The accumulation of carbon dioxide and water vapor in the atmosphere absorbs and retains heat so that it can’t escape into space: greenhouse effect.
Insolation: incoming solar radiation
 The intensity of insolation depends on the angle at which the sun’s rays strike Earth’s surface.
 When the sun is directly overhead, the angle of insolation is 90°, and Earth’s surface receives the maximum amount of energy.