The atmosphere is mainly composed of nitrogen, oxygen, and carbon dioxide. The carbon cycle involves photosynthesis, respiration, and combustion and works to maintain stable levels of oxygen and carbon dioxide. Early in Earth's formation, volcanoes released gases like carbon dioxide, water vapor, and ammonia into the atmosphere. Over time, the formation of oceans and evolution of plants increased oxygen levels while decreasing carbon dioxide. Human activities like increased population, fossil fuel combustion, deforestation, and transportation have led to higher atmospheric pollution levels and their associated health and environmental impacts. Strategies to control pollution include emissions standards, catalytic converters, and reducing carbon dioxide emissions.

1. C2f The Composition of the Atmosphere
• The air is mainly made up from 3 gases:
1. _____ oxygen;
2. _____ nitrogen;
3. _____ carbon dioxide
• The percentage of these 3 gases does not vary much (they are ____________).
• There are other gases in small amounts such as _______________ and some
____________ gases. Water varies – in high humidity e.g. when it is raining there
is a larger percentage in the air.
The Carbon Cycle
This cycle shows us how the levels of oxygen and carbon dioxide are kept constant
through the processes of photosynthesis, respiration and combustion.
1. respiration and combustion increase the level of carbon dioxide and decrease
the level of oxygen in the air.
2. photosynthesis decreases the level of carbon dioxide and increases the level
of oxygen in the air.

2. The Evolution of the Atmosphere
1. Degassing the interior of the Earth by Volcanoes
• When the Earth first formed it was ___________________ and the surface was
_____________________
• As it cooled a thin _________________ formed
• Because the crust was thin, __________________ kept erupting and gases from
inside the Earth were _______________. This process is called ___________.
• The main gas produced was ___________________, CO2 but also ___________,
H2O and _________________, NH3 were produced.
2. Formation of water
• Over time, the Earth _________________ and the steam _________________
to form water which became the oceans.
• A lot of carbon dioxide was removed from the atmosphere by _______________
in the oceans.
3. The evolution of green plants produced oxygen
• Green plants evolved over most of the Earth. As they _____________________
they removed carbon dioxide, ________ and produced oxygen, _____.
• Nitrogen gas was formed in two ways:
1. Ammonia reacted with ______________
2. Nitrogen was released by ________________________________
Note that nitrogen is very _________________. It is only nitrifying bacteria
(found in the roots of some plants) that can use nitrogen. It is not used up in
any other reactions and that is why the air is about 78% nitrogen.

3. Atmospheric Pollution
There are 3 main types of gas that pollute the atmosphere and you need to know
their names, where they come from and what environmental problems they cause:
Name Chemical Origin – where it comes Environmental problem
Formula from caused by gas
Carbon monoxide
Oxides of
nitrogen
Sulphur dioxide
How does human activity influence (affect) the composition of the air?
1. The human population is ______________, this means more people
_______________ and _________________________________ CO2.
2. __________________ demand for ______________ (heating, lighting, cooking)
means more burning of fossil fuels which produces more ____ and ______
3. Increasing demand for _____________ also burns fossil fuel producing CO2 and
SO2 .
4. _________________ means that trees are cut down for land
to build houses and grow food. This means that there are less
trees to absorb ______ in ____________________.
We need to control atmospheric pollution but HOW and WHY?

4. Why?
If pollutants build up in the atmosphere they can make people unwell e.g. the
number of people with ________________ has increased as atmospheric
pollution has increased.
How?
• ______________________________ in cars _______________ the amount
of carbon monoxide, CO (and nitrogen oxides) that cars produce.
• The catalytic converter contains a _____________________ made from
platinum and rhodium metals. It converts the poisonous __________________
to less harmful ______________________ in the following reaction:
+ +
Remember that CO2 leads to global warming so it is healthier for humans but still
has an impact on the environment.