Download Earth and Atmosphere

KS4
Changes to the Earth
and atmosphere
© Boardworks Ltd 2003
The Atmosphere
© Boardworks Ltd 2003
In the beginning • The Earth was formed about
4500 million years ago.
• The very first atmosphere mainly
consisted of hydrogen and
helium gases.
• Frozen giant planets like Saturn
and Jupiter still have
atmospheres like this but on the
warmer, smaller Earth these
light gases were largely lost into
space.
Jupiter
Saturn
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The early atmosphere
• During the first billion years on Earth
there was intense volcanic activity. This
produced the next early atmosphere.
• It would have contained large quantities
of carbon dioxide (CO2), along with
methane (CH4) , and ammonia (NH3).
• This is rather like the atmosphere on
Mars and Venus today.
• The Earth’s atmosphere would also
have contained water vapour which
condensed to form the oceans.
Mars
Venus
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Oxygen levels increase
• Carbon dioxide reacted with rocks and
much became trapped in them.
• The evolution of algae some 3000
million years ago, and subsequently
plants which successfully colonised the
Earth’s surface, led us towards the
present atmosphere.
• Their photosynthesis replaced carbon
dioxide with oxygen.
• Over a period of time billions of tonnes
of carbon dioxide became locked up in
fossil fuels.
Earth
Photosynthesis
increased
oxygen levels
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Nitrogen makes an appearance
• As oxygen levels rose atmospheric ammonia (NH3)
reacted with oxygen(O2) to form water(H2O) and
nitrogen (N2)
• Also, living organisms, including denitrifying bacteria,
broke down nitrogen compounds releasing more
nitrogen into the atmosphere.
• And so the atmosphere headed towards a composition
that has remained fairly constant for the last 200
million years.
21%
1%
Nitrogen
Oxygen
Other
78%
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Ozone – a vital filter
• Oxygen normally exists as pairs
of atoms (O2).
• Oxygen can, however, turn into
another form that has three
atoms joined together. This is
ozone (O3).
• As oxygen levels rose, so did
the amount of ozone.
• This layer of ozone in the
atmosphere filters out harmful
ultraviolet rays from the sun.
This will have allowed new
organisms to evolve and
survive.
3O2

Oxygen
2O3
ozone
Harmful UV rays stopped
with ozone layer
Earth
Harmful UV rays reach Earth’s surface
without ozone layer
© Boardworks Ltd 2003
Activity
Copy the timeline and arrange the blue
boxes in appropriate places along the line.
4500
million
No
gases
3000
million
H2O
N2 O2
2000
million
1000
million
CO2
NH3
CH4
500
million
Volcanoes
Algae
200 Now
million
H2
and
He
Plants
© Boardworks Ltd 2003
Answer
No
gases
Volcanoes
4500
million
3000
million
H2
and
He
Plants
Algae
2000
million
CO2
NH3 CH4
1000
million
500
million
200 Now
million
O2
N2 H2O
All positions are approximate
© Boardworks Ltd 2003
Activity
1. What was the main gas in the atmosphere around
3500M years ago?
Carbon dioxide
2. Where did this gas come from?
Volcanoes
3. What process led to reduction in CO2 levels?
Photosynthesis
4. What gas protects life from harmful UV radiation?
Ozone
5. What % of the present atmosphere is oxygen?
21%
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Activity
1. How long ago was the
atmosphere 75% CO2?
Approx 4,000M
2. How long ago were the
CO2 and N2 levels in the
atmosphere equal?
Approx 3,300M
3. How long ago was the
atmosphere 50%
nitrogen? Approx 2,000M
100%
Composition percentage
Use the graph to
estimate the answers.
carbon
dioxide
nitrogen
50%
oxygen
0%
5000 3000
now
0
Time (millions of years)
© Boardworks Ltd 2003
Activity
Find the words in the word-search
Write a sentence about how each has played a part in the
evolution of the Earth’s atmosphere.
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Ammonia
Carbon dioxide
Helium
Hydrogen
Methane
Nitrogen
Oxygen
Ozone
Photosynthesis
Volcano
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Carbon dioxide and temperature
Over millions of years the carbon cycle
has maintained a constant, low
percentage (approx. 0.03%) of carbon
dioxide in the atmosphere.
In 1860, the CO2 level was about 289
ppm (parts per million).
Here is a table showing the CO2
levels over a recent 10 year period.
Year
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
Carbon
Dioxide
(ppm)
333.68
335.55
337.14
338.38
340.25
341.82
343.18
344.26
345.99
347.96
What percentage change is this and does it matter?
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Greenhouse effect
From air trapped in Antarctic ice, we have a good idea of
CO2 concentrations going back 160,000 years.
We also know the temperatures over the same period.
The very warm interglacial period of 130,000 years ago was
accompanied by CO2 levels of around 300 ppm.
The previous great Ice Age had CO2 levels around 200 ppm.
200ppm
CO2
300ppm
CO2
Which label goes with each picture?
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Greenhouse effect
Normally the Earth absorbs heat
and emits heat at the same rate.
Because of this the temperature
remains constant.
Certain gases, like CO2 and
methane, act like a greenhouse.
They let heat in but do not let it
out.
This means: the more CO2 there
is, the hotter planet Earth is!
balanced
same
Earth
temp
More CO2
And
hotter
hotter!
hotter
Earth
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The Earth’s Structure
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The Earth’s Structure
Beneath the atmosphere the Earth consists of 3 main layers:
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The core
The core extends to about half the radius of
the Earth.
It is made mostly from iron and nickel and is
where the Earth’s magnetic field comes from.
It is very dense.
5500 C
The temperature is high and the outer
core is molten.
Towards the centre high pressure
makes the inner core solid.
1300 km
Intense heat is generated in the inner
core by decay of radioactive elements
like uranium.
1110 km
3000 km
Inner
Outercore
core
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The mantle
The mantle extends outwards from
the core to the crust: a distance of
about 2,900 km.
It is mostly a semi-molten liquid
upon which the Earth’s crust floats.
The heat coming from the core
generates convection currents in
the viscous mantle that cause the
crust above to move.
2900km
Mantle
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The crust
The crust is the thin layer of rock at
the surface upon which we live.
Eight elements make up over 98%
of the Earth’s Crust – although
they are virtually entirely in the
form of compounds.
50
% 45
40
35
30
25
20
15
10
5
0
20-60 km
O
Si
Al
Fe
Ca
Na
K
Mg
Crust
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What am I?
•
I am dense, very hot, made mostly of solid iron
and nickel.
Inner core
•
I’m iron and nickel too, but I’m liquid.
Outer core
•
I’m really very thin and am mostly silicon,
Crust
oxygen and aluminium
•
I’m a viscous semi-solid with convection
Mantle
currents circulating in me.
•
I just hang around on the outside.
Atmosphere
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Attach labels to the correct part of the diagram.
Atmosphere
Outer core
Crust
Mantle
Inner core
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Plate Tectonics
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Tectonic plates
•
•
•
•
The crust is made of about twelve plates.
These are like big rafts floating on the semi-molten
mantle.
Convection currents within the mantle cause the
plates to move.
Although they only move about 2 cm/year this can
have huge effects over long periods of time.
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Sea floor spreading
When two oceanic plates move apart
molten rock rises to the surface.
sea floor spreading
oceanic plate
magma rising
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Continental Drift
•
•
•
On average, the plates only drift
about 2cm/year. However 2cm
multiplied by a million is a long way!
Scientists think the continents were
originally all together in a supercontinent called Pangaea.
Over millions of years they have
drifted to their present positions on
the floating tectonic plates.
Pangaea
Millions
of years
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Continental Drift
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Evidence for Continental Drift
The theory is supported by several
pieces of evidence.
For example, if we consider Africa and
South America there is:
– The “jig-saw fit”
– The similarities in the rock layers
from Africa and South America.
– Similarities in the type and age of
fossils.
– Evidence of related species that
definitely did not swim the Atlantic
Ocean!
Jig Saw fit
Similar rocks
and fossils
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Plate boundaries
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Effects at Plate Boundaries
When a continental plate and an oceanic plate
meet, the effects include:
plates juddering past each other producing earthquakes
the continental plate buckles upwards whilst the
oceanic plate subducts (goes underground)
volcanoes result from the
rising magma (melted
oceanic plate)
volcano
oceanic
plate
magma rising
continental plate
© Boardworks Ltd 2003
Activity
• Find the words and
write a sentence
about how each one
has something to do
with plate tectonics.
– Drift
– Earthquake
– Fossil
– Jigsaw
– Magma
– Pangaea
– Plates
– Subduct
– Volcano
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© Boardworks Ltd 2003