1. 15.3 Layers of the atmosphere
Key concepts: What are the four main layers of the atmosphere?
What are the characteristics of each layer?
Key term:
Troposphere, stratosphere, mesosphere, thermosphere, ionosphere, exosphere

2. Layers: Four main layers (according to changes in TEMPERATURE)
Troposphere
Stratosphere
Mesosphere
Thermosphere

3. Troposphere Lowest layer of Earth’s atmosphere – means “turning”
Where weather happens
About 16 km above equator to 9 km above N. and S. poles
Contains almost all of the mass of the atmosphere
As altitude increases, temp decreases
For every 1 km increase in altitude, the air gets 6.5 degrees colder

4. Stratosphere
Stratosphere extends from the top of the troposphere to 50 km above Earth’s surface. Strato means “layer”
2nd layer of the atmosphere and contains the ozone layer
The lower stratosphere is cold, about -60 degrees C.
The upper part is warmer than the lower part. Why? Because there is more ozone in the middle of the stratosphere. The ozone absorbs energy from the sun, it is converted to heat and warms the air.
Ozone also protects from UV radiation.

5. Mesosphere Meso means “middle”
Begins 50 km above Earth’s surface and ends at 80 km. Temps around -90 C.
It protects the earth from being hit by a lot of meteoroids. (chunks of stone and metal from space)

6. Thermosphere Outermost layer of the atmosphere
Extends from 80 km above Earth’s surface outward into space.
It has no definite outer limit where it extends into space.
Thermo means “heat”
Even though the layer is very thin, it is very hot, up to 1800 degrees C. This is because sunlight hits the thermosphere first. Nitrogen and oxygen convert this energy into heat.

7. Ionosphere
The lower layer, called “ionosphere”, begins 80 km above the surface and extends to about 400 km.
Energy from the sun causes gas molecules to become electrically charged particles called ions.
Radio waves bounce off ions in the ionosphere back down to Earth’s surface
Auroras are created when particles from the sun enter the ionosphere near the poles, strike the atoms in the ionosphere and cause them to glow.

8. Exosphere Exosphere is the outer portion of the thermosphere.
Extends from about 400 km outward for thousands of kms.