Topic: Layers of the Atmosphere PSSA: 3.5.7.C / S8.D.2.1

Objective: TLW identify and describe the layers of Earth’s atmosphere.

MI #1: How is the atmosphere divided? The atmosphere is divided into layers based on temperature differences. Because atmospheric temperature is affected by what gases are present, the composition of the layers will be different.

MI #2: Troposphere The troposphere is the layer in which we live; this is where weather occurs. The prefix “tropo” means turning or change; the troposphere is the layer in which the gases turn over or mix. The troposphere makes up about 90% of the atmosphere’s total mass. The temperature in the troposphere decreases with altitude.

MI #3: Stratosphere The stratosphere is the layer above the troposphere. The prefix “strato” means layer; this is the atmospheric layer in which the gases do not mix much. The temperature increases with altitude due to the presence of the ozone layer, which traps heat and blocks out the sun’s harmful UV rays.

MI #4: Mesosphere The layer above the stratosphere is called the mesosphere. The prefix “meso” means middle; this is the atmosphere’s middle layer. It is the coldest layer and the temperature decreases with altitude.

MI #5: Thermosphere The uppermost layer of Earth’s atmosphere is the thermosphere. The prefix “thermo” means heat; this is the layer with the highest temperatures. Because the particles in the thermosphere are so far apart, they do not transfer much heat energy, so while temperatures are very high (1000 C), the thermosphere does not feel hot.

MI #6: Ionosphere The boundary between the mesosphere and the thermosphere is called the ionosphere. Nitrogen and oxygen atoms in this region absorb harmful solar energy and become ionized (charged). These ions radiate energy and create the auroras (northern and southern lights) that are seen near the poles.

So What? Real Life Application Understanding the layers of the atmosphere allows us to understand what happens as altitude changes.