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PHASE 1
· When the earth was formed it was molten and
stayed like this for millions of years. No
atmosphere could be formed as gases would just `boil
away' into space
· As it cooled a thin crust was formed. There were many
volcano eruptions, as the crust was only thin.
· When the volcanoes erupted they gave out carbon
dioxide, water vapour and nitrogen. This is how the
earliest atmosphere formed
· Oceans were formed when water vapour cooled down
and condensed
· This atmosphere was mostly carbon dioxide, with hardly
any oxygen. This is like Venus and Mars today.…read more

Slide 3

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PHASE 2
· Green plants formed because the C02 atmosphere allowed
them to perform photosynthesis.
· These plants caused C02 levels to fall and oxygen levels to
rise. This is because the word equation for photosynthesis is-
· Carbon dioxide+waterglucose+oxygen.
· They release the oxygen into the atmosphere.
· These plants were buried under layers of sediment when they
died, and they locked up all the C02 they had removed from
the air.
· The locked up C02 was present in sedimentary rocks as
insoluble carbonated and fossil fuels.
· This is why fossil fuels release C02, because they contain the
locked up C02 from millions of years ago.…read more

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PHASE 3
· The build up of oxygen from photosynthesis did not suit
many early organisms very well and they became extinct.
· However, lots of complex organisms evolved in this new
oxygen rich atmosphere and adapted/suited it well.
· The oxygen also caused the formation of the ozone layer
(03). This protects us from the harmful Ultraviolet (UV)
rays the sun emits.
· Even more complex organisms evolved because of the
ozone layer.…read more

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NOBLE GASES.
· Noble gases make up 1% of the atmosphere.
· They are group 0 of the periodic table. They are
· helium, neon, argon, krypton, xenon and radon.
· They are often known as inert gases, because they are all
chemically unreactive, existing as separate atoms.
· Argon is used in filament lamps (light bulbs)
· Neon is used in electric discharge tubes because when a
current is passed through neon it gives out a bright light.
· Helium is less dense than air so it is suited to be used in
balloons and airships.…read more

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CURRENT CHANGES IN THE ATMOSPHERE
· Factors increasing levels of C02....
· Burning fossil fuels releases C02.
· Deforestation. If there are less plants taking in C02
· and releasing oxygen, there will be increased
· amounts of C02 in the atmosphere.
· The amount of ozone in the ozone layer is decreasing...
· Holes in the ozone form over Antarctica every year.
· The ozone is broken down by manmade gases known as
CFCs, they were used in many aerosols and as fridge coolants
but stopped being used in the 1990s.
· The ozone layer protects us from harmful UV rays
· which can cause skin cancer.…read more

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