Layers of the Atmosphere

First Layer Scientists divide the atmosphere into FOUR main layers, based on changes in air temperature. The Troposphere (“tropo” = changing) Where Earth’s weather takes place, where we live. Lowest layer, extends from Earth’s surface to ~12 kilometers. Temperature decreases as altitude increases -60°C at top. Contains almost all of the mass in the atmosphere.

Stratosphere The Stratosphere (“strato” = layer) Second layer, above the troposphere Ranges from ~12 - ~50 km above Earth. Contains the ozone layer. The ozone layer is important because it protects us from dangerous UV radiation from the sun. The lower stratosphere is –60°C, but middle is warmer because of ozone, which absorbs heat from the sun.

Mesosphere The Mesosphere (“meso” = middle) Third layer, ~50 - ~80 km above Earth Protects Earth from being hit by meteoroids. Temperatures as cold as –90°C. As altitude increases in the mesosphere, temperature decreases.

Thermosphere The Thermosphere (“thermo” = heat) Outermost layer, ~80 km to outer space. Air in this layer is very thin, 0.001% as dense as the air at sea level. Temps are technically very hot since (up to 1,800°C) since it is the first layer to absorb heat from the sun. As altitude increases, temperature increases. QUESTION: Would you feel warm or cold if you were in the thermosphere, and why? Answer:

Two Layers of the Thermosphere 1. The ionosphere is the lower layer (~80-~400 km) and it contains gas molecules that are electrically charged due to the sun’s energy. Radio waves bounce back from the ionosphere to Earth’s surface. These bright light displays are called auroras. 2. The exosphere is the outer layer and it extends from 400 km outward for thousands of kilometers.

Ozone While ozone plays an important role in the stratosphere, it can be harmful in the troposphere. Why? Ozone is a pollutant that can form over cities from sun interacting with smoke and CO2, and can cause irritation to the lungs and eyes.