Unit 1 Theme 1.2 Our changing planet
The science in context Earth’s early
atmosphere had lots of carbon dioxide, but
no oxygen. Over time this changed – carbon
dioxide concentrations decreased and oxygen
increased. Nowadays, carbon dioxide is only
0.03% of the atmosphere, but it has a vital role
in keeping Earth’s surface warm. Environmental
scientists are beginning to understand this role
and its effect on climate change.
Sinking the Titanic
Figure 1: Melting ice
sheets could lead to
rising sea levels.
Icebergs can be spectacular, but dangerous! The
Titanic was famously sunk by colliding with an iceberg.
Changes over time
Following volcanic eruptions, Earth’s ‘second’
atmosphere consisted of water vapour, carbon dioxide,
ammonia and methane. Over time:
> Water vapour condensed to form Earth’s earliest
oceans.
> Oxygen gas began to form when carbon dioxide was
photosynthesised. At first this was by certain types of
bacteria and later by green plants.
> Nitrogen gas was produced partly by ammonia from
volcanoes reacting with oxygen and partly by
organisms such as denitrifying bacteria.
This led to the atmosphere that we have now – mainly
nitrogen and oxygen. Often, it is simply called air. Its
composition, based on ‘dry’ air, is shown in the table.
Formula
nitrogen
N2
78.1
oxygen
O2
20.9
argon
Ar
0.9
carbon dioxide
CO2
others
Questions
1 What gases were produced by Earth’s early
volcanic eruptions?
2 How was carbon dioxide removed from the
atmosphere?
3 How did the proportion of oxygen in the
Carbon dioxide
Carbon dioxide is produced by animals and plants in
aerobic respiration. This is a series of chemical reactions
in cells that can be summarised as:
glucose + oxygen
carbon dioxide + water + energy
Other natural processes such as forest fires and volcanic
eruptions also put carbon dioxide into the atmosphere.
Since the Industrial Revolution, burning fossil fuels has
added carbon dioxide faster than it can be removed.
fossil fuel + oxygen
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0.03
0.07
atmosphere go up?
Carbon dioxide in the atmosphere
% of the
atmosphere
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carbon dioxide + water + energy
… history of the earth’s atmosphere … gcse atmosphere
Questions
The proportion of carbon dioxide in our atmosphere is very small, but it
has a vital role in sustaining life. It traps heat from the Sun and helps keep
Earth’s surface warm. What happens:
4 Name two natural
processes that put carbon
dioxide into the atmosphere.
> Radiation from the Sun passes through Earth’s atmosphere.
5 Why did the Industrial
Revolution affect the
proportion of carbon dioxide
in the atmosphere?
> Heat is emitted back from Earth’s surface.
> Some of this heat passes through the atmosphere and back into space.
> Some is absorbed by carbon dioxide and keeps Earth’s surface warm
enough to support life.
6 Explain the importance of
Ideally, the amount of greenhouse gas in the atmosphere should be
enough to just balance what is needed to keep the temperature steady.
having carbon dioxide in our
atmosphere.
The more heat that is trapped in this way, the warmer the air becomes
and, therefore, Earth’s surface as well. Other gases that do this are called
greenhouse gases. Water vapour and methane are two examples.
There is strong evidence that the average global air temperature is rising.
This could lead to melting ice, rising sea levels and different weather
patterns (hotter summers, colder winters and more storms).
390
370
350
330
310
290
0.8
0.6
0.4
0.2
0
-0.2
-0.4
2000
1990
1980
1970
1960
1950
1940
1930
1920
1910
1900
1890
1880
> Carbon dioxide dissolved in the oceans. It became
‘locked up’ in sedimentary rocks such as limestone.
Gas
The importance of carbon dioxide
Temperature difference (oC)
Essential notes
>Earth’s atmosphere
changed over time
before reaching its
present composition
>carbon dioxide in the
atmosphere is essential
in sustaining life because
it traps heat from the
Sun, helping keep Earth’s
surface warm.
Carbon dioxide in the
atmosphere (parts per million)
A changing atmosphere
Year
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1000 1200 1400 1600 1800 2000
Year
Figure 2: The Industrial Revolution
began early in the 18th century.
Figure 3: Temperature difference compared
with the 1880 average. How much did the
average temperature of Earth’s atmosphere
increase between 1900 and 2000?
How do greenhouse gases work?
Radiation in the visible region of the
electromagnetic spectrum, with small amounts of
infrared radiation and ultraviolet radiation, passes
through Earth’s atmosphere.
the Sun
Light radiation has short wavelengths and,
therefore, high energy. Earth’s surface absorbs this
energy and emits it again as infrared radiation. This
has a longer wavelength and carries less energy.
Some infrared radiation is absorbed by greenhouse
gases and some escapes through the atmosphere
back into space.
Questions
7 Use scientific language to describe what the
diagram in Figure 4 shows.
… greenhouse gases
short-wavelength
solar radiation
long-wavelength
Earth radiation
Earth’s surface
Figure 4: The greenhouse effect.
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