C2F REVISION NOTES

Where our atmosphere came from

It is hard for us to imagine how old the Earth really is
It might help to think of the Earth's history as a 24 hour
clock; on this scale humans arrived on Earth at one second
to midnight

When the Earth was formed (about 4600 million years
ago) its atmosphere was probably made from hydrogen and
helium just like 99% of the universe
The Earth itself was a molten ball of rock

As the ball cooled down, a solid
crust formed on the outside
The molten rock underneath…

The oxygen was important because it turned into ozone (O
)
Ozone stops harmful rays from the Sun reaching the
surface, so it became possible to live out of the water

Some oxygen reacted with ammonia, giving off nitrogen
More nitrogen was formed by bacteria living in the soil
The…

Gases in the air




The ratio of gases are kept fairly constant by natural
cycles
Plants photosynthesis and all living things respire




Upsetting
the balance

Modern day
living is

upsetting the balance of gases in the atmosphere in a negative
way

Deforestation

Less oxygen (O ) being produced

Burning fossil fuels

Adding carbon dioxide (CO )

Industries and power stations

Adds sulphur dioxide and nitrogen oxide; causes acid rain
Other polluting and greenhouses gases
Carbon monoxide (CO) from incomplete…

Sensible deposal of old fridges