C2F REVISION NOTES

SINGLE SCIENCE, OCR BOARD - HIGHER TIER, CHEMISTRY - C2F

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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

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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 often
burst through the thin crust
Volcanoes was erupting all over the
Earth's new surface
These volcanoes gave out gases
just like volcanoes do today
The gases included ammonia (NH ), carbon dioxide (CO ),…read more

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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 levels of methane began to fall as it too reacted with
oxygen
Eventually, about 200 million years ago, the atmosphere
reached the mixture we have today of roughly 20% oxygen
and 80% nitrogen…read more

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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…read more

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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 burning of fossil
fuels (e.g.…read more

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Sensible deposal of old fridges…read more

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