1. Introduction to the Atmosphere
The air around us.

2. What is the atmosphere?
The Earth is surrounded by a blanket of air, which we call the atmosphere. It reaches over 560 kilometers (348 miles) from the surface of the Earth, so we are only able to see what occurs fairly close to the ground.
This “blanket” moderates temperature, protects us from harmful radiation and supports life.

3. Composition of the Atmosphere
The present composition of the atmosphere is:
21% OXYGEN (O2)
78% NITROGEN (N2)
0.04% CARBON DIOXIDE (CO2)
~0.9% ARGON (Ar)
Besides water vapor, several other gases are also present in much smaller amounts:
Carbon monoxide (formula CO)
Neon (Ne)
Oxides of nitrogen
Methane (CH4)
Krypton (Kr)

4. THE FIRST BILLION YEARS
The Earth's surface was originally molten, as it cooled the volcanoes out gassed out massive amounts of:
CARBON DIOXIDE,
STEAM (H2O vapor),
AMMONIA and
METHANE.
There was NO OXYGEN. The STEAM condensed to form water which then produced shallow seas.

5. Layers of the Atmosphere
Thermosphere(Ionosphere + exosphere)

6. The Troposphere
Troposphere: The troposphere is the lowest region in the Earth's (or any planet's) atmosphere.
On the Earth, it goes from ground (or water) level up to about 11 miles (17 kilometers) high.
Weather and clouds occur in the troposphere.
In the troposphere, the temperature generally decreases as altitude increases.

7. The Stratosphere
The stratosphere : 11 and 31 miles (17 to 50 kilometers) above the earth's surface.
The earth's ozone layer is located in the stratosphere. Ozone, a form of oxygen, is crucial to our survival; this layer absorbs a lot of ultraviolet solar energy.
Only the highest clouds (cirrus, cirrostratus, and cirrocumulus) are in the lower stratosphere.

8. The Mesosphere
The mesosphere : 31 and 50 miles (17 to 80 kilometers) above the earth's surface
Temperatures in the mesosphere drop with increasing altitude to about -100°C
In the mesosphere temperatures that quickly decrease as height increases.
The mesosphere is also the layer in which a lot of meteors burn up while entering the Earth's atmosphere. From the Earth they are seen as shooting stars.

9. The Thermosphere
Temperature increases with altitude. Due to the Suns energy.
Temperatures in this region can go as high as 1,727 degrees Celsius.
Radiation causes the scattered air particles in this layer to become electrically charged (see ionosphere), enabling radio waves to bounce off and be received beyond the horizon.
The thermosphere can be divided into two parts: the ionosphere and the exosphere.

10. The Ionosphere
The thermosphere can be identified in two parts- the ionosphere and the exosphere.
Ionosphere: 70 km-640 (about 400 miles = 640 km).
It contains many ions and free electrons (plasma).
Auroras occur in the ionosphere.
The Aurora , or northern lights are a result of particles from the sun coming into contact with the Earth’s atmosphere.

11. The Exosphere
Exosphere: the outermost layer of the Earth's atmosphere.
From about 400 miles (640 km) high to about 800 miles (1,280 km).
The lower boundary of the exosphere is called the critical level of escape, where atmospheric pressure is very low (the gas atoms are very widely spaced) and the temperature is very low
In this region, atoms and molecules escape into space.