1. Earth’s Atmosphere

2. Why is it important?
Without its atmosphere, Earth would be a very different planet.
Gases in the atmosphere allow:
plants to photosynthesize
animals and plants to engage in respiration.

3. Water Cycle Role of the atmosphere:
Water vapor, which is an atmospheric gas, is an essential part of the water cycle.

4. Weather All weather takes place in the atmosphere.
Weather describes what the atmosphere is like at a specific time and place.
Changes day to day.
This can include:
Temperature
Wind
Precipitation 

5. Climate
Climate is the long-term average of weather in a particular spot.
Example:
Weather for a particular winter day in Tucson, Arizona, may include snow, however, the climate of Tucson is generally warm and dry.

6. Ozone Ozone is a molecule composed of three oxygen atoms, (O3).
Located in the upper atmosphere.
Absorbs high-energy ultraviolet (UV) radiation coming from the Sun.
Without ozone for protection, only the simplest life forms would be able to live on Earth.

7. Atmospheric Gases
Keep Earth's temperatures within an acceptable range.
Greenhouse gases trap heat in the atmosphere so they help to moderate global temperatures.
Without an atmosphere with greenhouse gases, Earth's temperatures would be frigid at night and scorching during the day.
Important greenhouse gases include:
carbon dioxide, methane, water vapor, and ozone.

8. Composition of Air Nitrogen and oxygen make up 99% of the atmosphere.
Carbon dioxide and water vapor are very important , but a minor component.

9. Humidity Humidity is the amount of water vapor in the air.
Equatorial regions have higher humidity
Air temperatures are higher and warm air can hold more moisture than cooler air.
Humidity is lower near the polar regions because air temperature is lower.

10. Atmospheric Pressure
Air pressure is the force of air weighing down over a unit of area.
At higher altitudes, air pressure is lower.
This bottle was closed at an altitude of 3,000 meters where air pressure is lower. When it was brought down to sea level, the higher air pressure caused the bottle to collapse.
If your ears have ever "popped", you have experienced a change in air pressure. Gas molecules are found inside and outside your ears. When you change altitude quickly, like when an airplane is descending, your inner ear keeps the density of molecules at the original altitude. Eventually the air molecules inside your ear suddenly move through a small tube in your ear to equalize the pressure. This sudden rush of air is felt as a popping sensation.

11. Layers of the Atmosphere
Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere

12. Layers of the Atmosphere
Divided into layers based on how the temperature in that layer changes with altitude.
The temperature gradient in each layer is determined by the heat source of the layer.

13. The layers of the atmosphere appear as different colors in this image from the International Space Station.

14. Troposphere The lowest layer that is closest to Earth’s surface.
Where most of the atmospheric gases are located.
All of the planet’s weather
occurs here.
Heated from the ground,
so temperature decreases
with altitude.
Because warm air rises and cool air
sinks, the troposphere is unstable.

15. Temperature Inversion
When air temperature increases with altitude.
Warm air sits over cold air.
Inversions form:
Over land at night or in winter when the ground is cold.
The cold ground cools the air that sits above it, making this low layer of air denser than the air above it.
Near the coast where cold seawater cools the air above it.
When that denser air moves inland, it slides beneath the warmer air over the land.

16. Thermal Inversion
Since temperature inversions are stable, they often trap pollutants and produce unhealthy air conditions in cities.

17. Stratosphere Temperature increases with altitude.
Contains the ozone layer, which protects the planet from the Sun’s harmful UV radiation.
The Sun is the direct heat source for the stratosphere.
Air in the stratosphere is stable
because warmer, less dense air
sits over cooler, denser air.
As a result, there is little mixing of
air within the layer.

18. Even with the ozone layer, UVB radiation still manages to reach Earth's surface, especially where solar radiation is high.

19. Mesosphere Temperatures decrease with altitude.
Few gas molecules in the mesosphere to absorb the Sun’s radiation.
Heat source is the
stratosphere below.

20. Meteors burn in the mesosphere even though the gas is very thin; these burning meteors are shooting stars.

21. Thermosphere
The density of molecules is so low that one gas molecule can go about 1 km before it collides with another molecule.
Since so little energy is transferred, the air feels very cold.

22. Ionosphere Located within the Thermosphere.
Contains ionized particles due to solar radiation.
When the Sun is active, more ionization occurs.
Makes long distance radio communication possible.

23. Magnetosphere
The magnetic field of the Earth is surrounded in a region called the magnetosphere.
Prevents most of the particles from the sun, carried in solar wind, from hitting the Earth.

24. Solar Wind Beyond the atmosphere. Made of high-speed particles
mostly protons and electrons, traveling rapidly outward from the Sun.
The aurora is formed when protons and electrons from the Sun travel along the Earth's magnetic field lines. These particles from the Sun are very energetic. We are talking major-league energy, much more than the power of lightning: 20 million amps at 50,000 volts is channeled into the auroral oval. It's no wonder that the gases of the atmosphere light up like the gases of a streetlamp! The aurora is also known as the northern and southern lights. From the ground, they can usually be seen where the northern and southern auroral ovals are on the Earth. The northern polar auroral oval usually spans Fairbanks, Alaska, Oslo, Norway, and the Northwest Territories. Sometimes, when the Sun is active, the northern auroral oval expands and the aurora can be seen much farther south.
The lights of the aurora come in different colors. Oxygen atoms give off green light and sometimes red. Nitrogen molecules glow red, blue, and purple.

25. Aurora
The particles from solar wind that enter the magnetosphere create the aurora lights.
Different elements give off different colors.
Oxygen= green (sometimes red)
Nitrogen= red, blue and purple

26. Exosphere The outermost layer of the atmosphere.
Gas molecules are so scarce that at some point there are no more.

27. Imagine Earth with No Atmosphere
What happened to Mars?