The atmosphere is divided into four main layers - the troposphere, stratosphere, mesosphere and thermosphere. The troposphere contains around 75% of the atmosphere's mass and is where most weather occurs. It contains uniform mixtures of gases. The stratosphere is around 50km thick and contains 1000 times less water but 1000 times more ozone than the troposphere. Greenhouse gases like carbon dioxide and water vapor in the troposphere absorb and re-emit infrared radiation, warming the Earth's surface and allowing life to exist.

2. Atmosphere
Thin envelope of
Weather gases that surrounds Climate
the planet.
The state of the Weather conditions
atmosphere at a at a locality averaged
given place and time over a specified time
period

4. Atmosphere is divided into four
distinct zones of contrasting
temperature due to differential
absorption of solar energy.
There is little mixing between
layers.
As you move higher in altitude
the atmosphere thins out.

5. Troposphere contains about
75% of the mass the earth’s air,
but is only about 17km thick.
Most weather events occur here.
It’s composition is uniform due
to mixing caused by winds.
Temperatures drop with altitude.
The sharp boundary in
temperature at the tropopause
limits mixing with upper layers

6. Stratosphere extends to about
50km thick.
Similar in composition to the
troposphere except in two ways.
It contains1000 times less water
and is 1000 times higher in
ozone.
Ozone is produced by lightning
and solar irradiation of oxygen
molecules.
The Stratosphere is relatively
calm, volcanic ash or human
caused pollution can remain in
suspension in the stratosphere
for many years.

7. Past and Present Composition
The composition of the Earth’s atmosphere has changed since the
formation of the Earth. The Earth’s first atmosphere was mainly
helium and hydrogen. Volcanic emissions later added carbon
dioxide, nitrogen, water, sulfur dioxide and other elements.

8. Large amounts of carbon dioxide from volcanoes caused the
Earth’s past climate to be warmer than today’s.
Without carbon dioxide no life could be present on earth. Primitive
bacteria and algae in oceans could now photosynthesis.

9. But no life on land due to solar radiation from the sun.
But life in oceans is protected from radiation and can
develop due to presence of carbon-dioxide

11. Free oxygen gas was absent in the earth’s early atmosphere.
Any oxygen produced by photosynthesis reacted with other chemicals
and was trapped in the form of oxide compounds in rock, Fe2O3 .
It took millions of years before oxygen was present as a gas in the
atmosphere
Nearly all the molecular oxygen in the atmosphere today was
produced by photosynthesis.
Sunlight + CO2 + H2O → O2 (g) + C6H12O6
Living organisms are responsible for the evolution of our
atmosphere. Free oxygen made it possible for life to evolve on land.
Before large amounts of free oxygen were present in the
atmosphere, lethal intensities of solar radiation flooded the Earth’s
surface.
Free oxygen reacts in the stratosphere to form ozone (O3). This ozone
layer shields the Earth’s Surface from lethal radiation.

12. Oxygen produced by photosynthesis builds up in the atmosphere. This
turns into ozone due to solar radiation.

13. Gas Symbol Percent by Volume
Nitrogen N2 78.08 %
Oxygen O2 20.94 %
Argon Ar 0.934 %
Carbon Dioxide CO2 0.033 %
Neon Ne 0.00182 %
Helium He 0.00052%
Methane CH4 0.00015 %
Krypton Kr 0.00011 %
Hydrogen H 0.00005 %
Nitrous oxide N2O 0.00005 %
Xenon Xe 0.000009 %
Water vapor varies depending on the location. From 0.01% to 5%

14. Suspended particles within the Atmosphere are called aerosols.
Aerosols can be both solid and
liquid. Some are too small to
see, other are clustered together
and can be seen as clouds.
Volcanoes are one major
source of natural aerosols

15. How does the Earth keep itself warm?
The average radiant energy from the sun falling on the surface
at about 343 watts /m2.
As it passes through the atmosphere, 6% is scattered back into
space by atmospheric molecules.10% is reflected back into
space from land and ocean surface.
The remaining 84% actually heats up the surface.
To balance this the Earth itself needs to radiate the same
amount of energy back into space.
The Earth emits long-wave length radiation in the form of
infrared radiation. (this depends on the temperature of the
surface and the type of surface)
But the amount of energy is not balanced.

16. Nitrogen and Oxygen gas can neither absorb or emit thermal radiation.
It is Water vapor, carbon dioxide, and some other minor gases which
absorb long-wave thermal radiation leaving the surface.
This is why the average surface temperature is 15°C instead of
-6°C which it should be it balanced.
1. Solar radiation
2. Radiation from
greenhouse gases
3. Radiation scattered
by atmosphere.

17. Some wavelengths of radiation from the Earth can escape into space
if there are no clouds. Other wavelengths are absorbed by gases and
re-emitted into space or back to the surface.
Graph of radiation emitted from Earth’s surface that is
absorbed by the Atmosphere.

18. Absorption of solar energy by the atmosphere is selective.
Visible light passes through, ultraviolet is absorbed mostly by
ozone in the stratosphere. Infrared is absorbed mostly by carbon
dioxide and water in the troposphere.

20. Solar Radiation and the Atmosphere