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KS4 Chemistry
Earth and Atmosphere
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Contents
Earth and Atmosphere
Development of the atmosphere
O3 and CO2
The Earth’s structure
Plate tectonics
Rocks
Summary activities
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The early atmosphere
• The Earth was formed about 4,500
million years ago.
Mars
• During the first billion years there was
intense volcanic activity, which produced
the early atmosphere. This would have
contained large quantities of carbon
dioxide (CO2) and water vapour. Methane
(CH4) and ammonia (NH3) are thought to Venus
have also been present.
• This is rather like the atmosphere on
Mars and Venus today.
• The water vapour condensed to form the
oceans.
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Oxygen levels increase
• Carbon dioxide reacted with rocks and
much became trapped in them.
Earth
• The evolution of algae some 3,000
million years ago, and subsequently
plants which successfully colonized 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.
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Photosynthesis
increased
oxygen levels
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Nitrogen appears
• 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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Atmosphere timeline
Copy the timeline and arrange the blue
boxes in appropriate places along the line.
4,500
million
No
gases
3,000
million
H2O
N2 O2
2,000
million
1,000
million
CO2
NH3
CH4
500
million
Volcanoes
Algae
200 Now
million
H2
and
He
Plants
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Timeline answers
No
gases
Volcanoes
4,500
million
3,000
million
H2
and
He
Plants
Algae
2,000
million
CO2
NH3 CH4
1,000
million
500
million
200 Now
million
O2
N2 H2O
All positions are approximate
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Changing gas levels
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
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100%
Composition percentage
Use the graph to
estimate the answers.
carbon
dioxide
nitrogen
50%
oxygen
0%
5,000 3,000
now
0
Time (millions of years)
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Contents
Earth and Atmosphere
Development of the atmosphere
O3 and CO2
The Earth’s structure
Plate tectonics
Rocks
Summary activities
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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).
3O2

oxygen
2O3
ozone
Harmful UV rays stopped
with ozone layer
• As oxygen levels rose, so did the
amount of ozone.
Earth
• This layer of ozone in the
atmosphere filters out harmful
ultraviolet rays from the sun. This
will have allowed new organisms
Harmful UV rays reach Earth’s surface
to evolve and survive.
without ozone layer
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The carbon cycle
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CO2 release or consumption?
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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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Changing CO2 concentrations
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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The 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 is called the greenhouse
effect.
balanced
same
Earth
temp
More CO2
And
hotter
hotter!
hotter
Earth
This means that the more CO2 there
is, the hotter planet Earth is!
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Contents
Earth and Atmosphere
Development of the atmosphere
O3 and CO2
The Earth’s structure
Plate tectonics
Rocks
Summary activities
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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.
5,500 C
The temperature is high and the outer
core is molten.
Towards the centre, high pressure
makes the inner core solid.
Intense heat is generated in the inner
core by the decay of radioactive
elements like uranium.
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1,300 km
1,110 km
3,000 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.
2,900km
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
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Si
Al
Fe
Ca
Na
K
Mg
Crust
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What am I?
•
I’m a viscous semi-solid with
convection currents circulating in me.
Mantle
•
I’m iron and nickel too, but I’m liquid.
Outer core
•
I just hang around on the outside.
Atmosphere
•
I’m really very thin and am mostly
silicon, oxygen and aluminium.
Crust
•
I am dense, very hot, made mostly of
solid iron and nickel.
Inner core
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Sections of the Earth
Atmosphere
Outer core
Crust
Mantle
Inner core
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Contents
Earth and Atmosphere
Development of the atmosphere
O3 and CO2
The Earth’s structure
Plate tectonics
Rocks
Summary activities
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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 a year this can
have huge effects over long periods of time.
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Why do plates move?
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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
super-continent called Pangaea.
•
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Pangaea
Millions
of years
Over millions of years they have
drifted to their present positions on
the floating tectonic plates.
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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 “jigsaw 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!
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Jigsaw 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 while the oceanic
plate subducts (goes underground)
• volcanoes result from the
rising magma (melted
oceanic plate)
volcano
oceanic
plate
magma rising
continental plate
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Contents
Earth and Atmosphere
Development of the atmosphere
O3 and CO2
The Earth’s structure
Plate tectonics
Rocks
Summary activities
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Types of rocks
There are three main types of rocks:
Igneous – formed when molten rock cools.
Sedimentary – formed by the “cementing together” of
small grains of sediment.
Metamorphic – rocks changed by the effect of heat
and pressure.
All of these are involved in a continuous flow of rock from
the surface underground only to emerge again later as part
of the on-going rock cycle.
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Igneous rocks
•
These are rocks formed by the cooling of molten
rock (magma).
Magma cools
and solidifies
forming
igneous
rocks.
volcano
magma
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Types of igneous rocks
Igneous rocks divide into two main groups:
• Intrusive igneous
• Extrusive igneous
• Intrusive igneous
rocks, like granite,
are formed when
magma solidifies
within the ground.
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• Extrusive igneous
rocks, like basalt,
are formed when
magma solidifies
above the ground.
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Igneous rocks and crystal size
The more slowly a rock changes from liquid to solid the
bigger the crystals grow.
Intrusive igneous rocks,
like granite, usually have
clearly visible crystals.
Intrusive igneous
rocks that cool
really slowly can
have very big
crystals.
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Extrusive igneous rocks,
like basalt, have crystals
that are usually small.
Extrusive igneous
rocks that cool
really quickly can
have a glassy
appearance.
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Chemical and physical weathering
•
Surface rocks seem to be gradually reduced in size by
weathering processes.
•
Chemical weathering occurs when chemicals, such as
those in acid rain, ‘eat’ away certain rocks.
•
Physical weathering relates to rocks being broken down
by the action of wind, rain and sun. For example, during
the freezing and thawing of water in the cracks of rocks,
the expansion of water makes the rocks splinter.
•
The small broken fragments wash into rivers and,
eventually, reach the sea where they settle as sediment.
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Sedimentary rocks
Sedimentary rocks are rocks formed when particles
of sediment build up and are “cemented together”
by the effect of pressure and minerals.
Fragments washed to the sea
Rocks are broken
up by the action
of weather
sea
Sedimentary
rocks
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Types of sedimentary rocks
Sedimentary rocks tend to have visible grains of sediment.
Sometimes they contain fossils.
They are usually softer than igneous rocks.
Examples of sedimentary rocks are sandstone and mudstone.
Getting older
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Sandstone is
formed from the
cementing
together of
grains of sand.
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Metamorphic rocks
Metamorphic rocks are formed by the effect of heat and
pressure on existing rocks.
This can greatly affect the hardness, texture and layer patterns
of the rocks.
Pressure from
surface rocks
metamorphic
rock
magma
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forming
here
heat
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Types of metamorphic rocks
Marble, slate and schist are metamorphic.
Limestone is a rock often formed from the sediment of
shells. Temperature and pressure cause the rock to
reform as small crystals that are much harder. This is
marble. It is used as a hard and decorative stone in
buildings, sculptures etc.
Slate is formed when pressure squeezes mudstone into
plate-like grey sheets. It is used in roofing.
Schist and mica are formed when mudstone is subjected to
very high temperatures and pressure. Again, they
contain layers, which is typical of many (but not all)
metamorphic rocks.
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What’s the rock?
Match the rock with the correct description.
Give an example of this type of rock.
Rock type
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Description
intrusive
igneous
Large crystals, hard rock
metamorphic
Sandy texture, soft rock
extrusive
igneous
Small crystals, hard rock
sedimentary
Wavy layers of crystals
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The rock cycle
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Contents
Earth and Atmosphere
Development of the atmosphere
O3 and CO2
The Earth’s structure
Plate tectonics
Rocks
Summary activities
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Glossary (1)
 atmosphere – The gases that surround the Earth.
 core – The central part of the Earth, divided into a solid
inner section and molten outer section.
 crust – The outer section of the Earth, made up of plates.
 igneous – A rock formed by the crystallization of magma.
 mantle – The layer of molten, semi-solid rock under the
Earth’s crust.
 metamorphic – A rock formed when an existing rock is
changed by heat or pressure.
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Glossary (2)
 ozone – A gas made up of three oxygen atoms, which
forms a layer that filters harmful UV rays from the sun.
 plate – A large section of rock that floats on the Earth’s
mantle and forms part of the crust.
 plate tectonics – A theory that movement of the Earth’s
plates over time is responsible for the current position of
continents, and the creation of mountains and volcanoes.
 sedimentary – A rock made up of layers of sediment.
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Anagrams
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Multiple-choice quiz
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