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Chapter 3 – The
Dynamic Earth
Section 2 – The
Atmosphere
Mr. I
Objectives
• Describe the composition of the Earth’s
atmosphere.
• Describe the layers of the Earth’s atmosphere.
• Explain three mechanisms of heat transfer in Earth’s
atmosphere.
• Explain the greenhouse effect.
Composition of the Atmosphere
The atmosphere is a mixture of gases
that surrounds a planet, such as Earth.
• Made up of :
Nitrogen – 78%
Oxygen, - 21%
Carbon dioxide - 0.04%,
Other gases – like H20, Methane
etc.
Composition of the Atmosphere
• As well as having gases, the Atmosphere also contains atmospheric dust.
• Atmospheric dust = tiny particles, solid particles suspendered in the
atmosphere.
• Usually atmospheric dust is made up of soil, salt, ashes, skin ,hair, pollen
etc…
The Atmosphere
• Gases can be added to and removed from the atmosphere through living
organisms and other physical processes of the Earth.
• For example, animals remove oxygen when they breathe in and add carbon
dioxide when they breath out.
• Oceans absorb or release CO2 based on concentrations of CO2 in the
atmosphere.
• Combustion adds CO2 to the atmosphere and removes Oxygen.
Purpose of the Atmosphere
• Primarily the function of the atmosphere is to insulate the planet. – If Earth
did not have an atmosphere, the average temperature would be -450F.
• The atmosphere acts like a blanket around the Earth and keeps heat from
easily escaping back into space.
• The other main function is to provide gasses for life, like Oxygen and carbon
dioxide.
Air Pressure
Air Pressure – is the pressure exerted by the weight of air in the atmosphere
of Earth
Higher pressure near the surface of the Earth and Lower Pressure as we
increase in altitude.
Layers of the Atmosphere
Four layers of the atmosphere -
1. Troposphere – All weather occurs in
this layer, gets colder as altitude
increases in this layer
2. Stratosphere – Contains Ozone which
reflects U.V radiation, temp. rises as
altitude increases in this layer
3. Mesosphere – coldest layer
4. Thermosphere – hottest layer – very
thin layer.
• Layers are based by temperature
Energy Transfer in the Atmosphere
• All Energy on Earth comes from the sun through
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electromagnetic waves!
Energy comes from the sun through space through
Radiation - electromagnetic waves.
These electromagnetic waves then pass through
the atmosphere without being absorbed.
They are then absorbed by the Earth’s surface,
which then re-radiates them out as long wave
radiation.
This long wave radiation is then absorbed by gases
in the atmosphere called green house gases.
Energy Transfer in the Atmosphere
• These greenhouse gas molecules pass their energy from one another in the
atmosphere by colliding with each other in a process called conduction.
• Next the warm molecules rise as the cooler ones fall in a process called
convection.
• This then gives rise to high and low pressure zones on the Earth
generates winds! And weather!
The Greenhouse Effect
• The Greenhouse Effect – the absorption
of long wave radiation from the Earth by
carbon dioxide, water vapor and other
greenhouse gasses
• If there was no greenhouse effect on
Earth, it would be too cold for life to
exist.