Download Earth and Atmosphere

KS4
Changes to the Earth
and atmosphere
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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
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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
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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
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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)
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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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Rocks
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Types of rocks
There are three main types of rocks:
1.Igneous - formed when molten rock cools.
2.Sedimentary – formed by the “cementing together”
of small grains of sediment.
3.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.
• 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.
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 is when chemicals, such as those
in acid rain, ‘eat’ away certain rocks.
•
Physical weathering is to do with the 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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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
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 or layer
patterns of the rocks.
Pressure from
surface rocks
metamorphic
rock
Magma
forming
here
heat
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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. 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 as well as
pressure. Again they contain layers which is
typical of many (not all) metamorphic rocks.
© Boardworks Ltd 2003
Activity
Match the rock with the correct description.
Give an example of this type of rock.
Rock type
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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Activity
Crack the code! What should this really say?
•
Weathering
(Giant
hewer) leads to fragments collecting in the
sea and forming (amsedimentary
seen dirty) rocks such as
mudstone
sandstone
chalk, (sum
to end) and (and
so nest).
•
pressure
metamorphic
Heat and (perusers)
can lead to (a chem
import)
rocks such as (stale)
and (ambler).
slate
marble
•
Some of these will melt and eventually cool as
intrusive
they approach the surface to form (I ruin
vets)
(goigneous
in use) rocks such as (get
rain).
granite
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What gases would have formed the original
atmosphere around planet Earth?
1.
2.
3.
4.
Hydrogen and helium
Oxygen and nitrogen
Methane and ammonia
Carbon dioxide and water
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What gases form the majority of the present
atmosphere around planet Earth?
1.
2.
3.
4.
Hydrogen and helium
Oxygen and nitrogen
Methane and ammonia
Carbon dioxide and water
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What gas protects us against dangerous UV
radiation?
1.
2.
3.
4.
Sulphur dioxide
Nitrogen oxide
Methane
Ozone
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What gas is a major cause of the greenhouse
effect?
1.
2.
3.
4.
Sulphur dioxide
Nitrogen oxide
Carbon dioxide
Chlorine dioxide
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What process increases atmospheric carbon
dioxide levels?
1.
2.
3.
4.
Photosynthesis
Respiration
Formation of Fossil fules
Formation of carbonate rocks
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What layer of the Earth is around 50Km thick
and high in silicon and oxygen?
1.
2.
3.
4.
Inner core
Outer core
Mantle
Crust
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What layer of the Earth is mostly molten iron
and nickel?
1.
2.
3.
4.
Inner core
Outer core
Mantle
Crust
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What layer of the Earth is made of viscous
semi-molten magma?
1.Inner core
2.Outer core
3.Mantle
4.Crust
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What type of rock is formed by solidification of
molten magma?
1.
2.
3.
4.
Igneous
Metamorphic
Sedimentary
Fossilised
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What type of rock is formed by cementation of
small particles of weathered rock?
1.
2.
3.
4.
Igneous
Metamorphic
Sedimentary
Fossilised
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What type of rock is formed by the effect of heat
and pressure upon other rocks?
1.
2.
3.
4.
Igneous
Metamorphic
Sedimentary
Fossilised
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What type of rock is least likely to contain
fossils?
1.
2.
3.
4.
Igneous
Metamorphic
Sedimentary
Fossilised
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What is the process where tectonic plates
separate and magma creates new solid crust?
1.
2.
3.
4.
Weathering
Ageing
Sea floor spreading
Sedimentation
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What is the process where tectonic plates move
gradually apart?
1.
2.
3.
4.
Continental breakfast
Continental drift
The rock cycle
Subduction
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Which of these is not evidence for continental
drift theories?
1.
2.
3.
4.
Similarities of fossils
Similarities of rock layers
Jig-saw fit of coastal shapes
Similarities of climate
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