Triple Chemistry GCSE AQA Grade 9 Unit 9 Chemistry of the Atmosphere Notes

Unit 9: Chemistry of the Atmosphere
The Earth’s Atmosphere
The Earth’s atmosphere has changed a lot since the formation of the Earth 4.6 billion years ago.

TIMESCALE CONDITION OF THE KEY FACTS AND EVENTS THAT
ATMOSPHERE SHAPED THE ATMOSPHERE
Intense volcanic activity releases:
Formation of the - Mainly CO2 (like the
Earth atmospheres of Mars and
Venus today)
- Water vapour (which
condenses to form oceans)
- Small proportions of
methane and ammonia
4 billion years - Nitrogen (which gradually
ago built up in the atmosphere)
Green plants and algae evolve and:
- CO2 is reduced as the plants
take it in and give out
3 billion years oxygen
ago - Microorganisms that can’t
tolerate oxygen are killed
off
- Carbon from CO2 becomes
2 billion years locked up in sedimentary
ago rocks formed from shells
and skeletons of marine
organisms
- Other gases react with
1 billion years oxygen to release nitrogen
ago - Nitrogen is also produced
by bacteria removing
nitrates from decaying
plant material
There is now about 20% oxygen and
about 80% nitrogen in the
atmosphere
Now The amount of CO2 has decreased
significantly


The Atmosphere Today
 The proportions of gases have been more or less the same for about 200 million years
 Water vapour may also be present in varying quantities (0 - 3%)

Early Now
Gas: % in atmosphere
Nitrogen 2% 78%
Oxygen 0% 21%
Carbon dioxide 92% 0.03%
Argon 0% 0.9%
Methane 2% 0%
Ammonia 1% 0%
Water 3% 0.07%




Decrease in CO2 and Increase in O2 and

, Increase of Oxygen Levels
 Algae and plants photosynthesise
 During photosynthesis CO2 and H2O react to produce C6H12O6
 Algae first started producing oxygen about 2.7 billion years ago
 Over the next billion years plants evolved and O2 levels in the atmosphere increased
 Eventually the level of O2 in the atmosphere increased enough to allow animals to evolve

Decrease of Carbon Dioxide Levels
 As plants and algae have evolved CO2 levels in the atmosphere have decreased
 This is because plants use CO2 during photosynthesis
 Carbon also becomes locked up in sedimentary rocks (e.g. limestone) and fossil fuels (e.g.
Increase in O2 and
coal, crude oil, natural gas) N2
Decrease in CO2
 Limestone contains calcium carbonate (CaCO3) and is formed from the shells and skeletons
of sea creatures
 Coal is a sedimentary rock formed from plant deposits that were buried and compressed
over millions of years
 The reaction between CO2 and sea water has also reduced CO2 levels, it produces:
- insoluble carbonates that are deposited as sediment
- soluble hydrogen carbonates
 Too much CO2 dissolving in the oceans can harm marine life – e.g. coral reefs.

Greenhouse Gases
 The Sun emits short-wavelength, high
energy radiation CO2CH4
- e.g. UV which is absorbed by and H2O
warms the Earth
 The Earth emits long-wavelength,
lower energy radiation and loses heat
- e.g. infrared thermal radiation
 Greenhouse gases absorb some of this
radiation
 This warms the atmosphere
 Without them the Earth would be too
cold for water to be liquid and couldn’t
sustain life



The Impact of Human Activities
 Increase the levels of greenhouse gases in the atmosphere




Carbon Methane

 CO2 levels have increased over the last  Cattle farming:
100 years - cattle produce methane and are
 Burning fossil fuels: reared for humans (consumption
- the increase correlates with the of beef and milk)