Download KS4-Earth-and-Atmosphere

KS4 Changes to
the Earth and
atmosphere
© Boardworks Ltd 2001
The Atmosphere
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In the beginning • The Earth was formed about
4500 million years ago.
• The very first atmosphere
mainly consisted of
hydrogen and helium gases.
• Frozen giants of 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, reacted with 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
3O2 
2O3
pairs of atoms (O2).
Oxygen
ozone
• Oxygen can, however, turn into
another form that has three
UV rays
With ozone
atoms joined together. This is Harmful
stopped
layer
ozone (O3).
• As oxygen levels rose, so did
the amount of ozone.
• This layer of ozone in the
Earth
atmosphere filters out harmful
ultraviolet rays from the sun.
This will have allowed new
organisms to evolve and
Harmful UV rays
Without ozone
survive.
Reach Earth’s surface layer
© Boardworks Ltd 2001
Activity
• Copy the timeline and arrange the yellow
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 2001
Answer
• All positions are approximate
No
gases
Volcanoes
4500
million
3000
million
H2
and
He
Algae
2000
million
CO2
NH3 CH4
1000
million
Plants
500
million
200 Now
million
O2
N2 H2O
© Boardworks Ltd 2001
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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© Boardworks Ltd 2001
Activity
1.
2.
3.
4.
5.
Do these processes release or consume
carbon dioxide?
release
Burning of fossil fuels.
Dissolving in the oceans. consume
Heating of limestone in lime kilns release
Respiration in animals.
release
Photosynthesis in plants. consume
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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). Alongside is data
showing the CO2 levels over
a recent 10 year period.
What percentage change is this and
does it matter?
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
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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.
•Which label goes with each picture?
200ppm
CO2
300ppm
CO2
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Greenhouse Effect
•
•
•
•
The link between carbon dioxide
and temperature is because CO2 is
a greenhouse gas.
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:
–The core
–The mantle
–The crust
–The core is itself made
up of two parts:
–An outer liquid core
–An inner solid core
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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
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 decay of radioactive elements
like uranium.
5500 C
1300km
1110km
3000km
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 virtually entirely in the
form of compounds.
50
% 45
Crust
40
35
30
25
20
15
10
5
0
20-60km
O
Si
Al
Fe
Ca
Na
K
Mg
© Boardworks Ltd 2001
Activity
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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Activity
•
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
•
•
•
Under the oceans molten rock rises to the surface
pushing apart the oceanic plate of the sea bed.
Where this plate meets the continental plate it is forced
back downwards.
The continental plate may just move or it may buckle
upwards to form mountain ranges.
sea floor spreading
Oceanic plate
Continental
plate
Continental
plate
Continental
plate
b a s al t i c c u s t
r
Magma rising and cooling
Rock melting
back into magma
© Boardworks Ltd 2001
Continental Drift
•
•
•
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.
Over millions of years they
have drifted to their present
positions on the floating
tectonic plates.
Pangaea
Millions
of years
© Boardworks Ltd 2001
Evidence for Continental Drift
•
The theory is supported by
several pieces of evidence.
E.g. 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
•
•
Where plates meet the surface is unstable.
Effects include:
– plates juddering past each other producing Earthquakes.
– Both plates buckling upwards producing mountains.
– One plate buckling upwards whilst the other subducts
(goes underground.)
– Volcanoes from the pressure forcing molten subducted
rock back to the surface.
volcano
Continental
plate
Oceanic plate
Magma
rising
magma
Rock melting
back into magma
© Boardworks Ltd 2001
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.
© Boardworks Ltd 2001
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.
© Boardworks Ltd 2001
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.
© Boardworks Ltd 2001
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 water
trapped in cracks in the rock. During freezing
and thawing 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.
© Boardworks Ltd 2001
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
© Boardworks Ltd 2001
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
© Boardworks Ltd 2001
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
© Boardworks Ltd 2001
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 2001
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
© Boardworks Ltd 2001
The Rock Cycle
Volcano
Extrusive
Igneous
Rocks, basalt
Rises to surface
where it
cools rapidly
Rocks are broken
up by the action
of weather
Rocks rise
to surface by
uplift and erosion
sea
Intrusive
Igneous rocks
granites,
Slow
solidification
Sedimentary
rocks, mudstone
High pressure
and temperature
Metamorphic
rocks, slate and
marble
magma melt
© Boardworks Ltd 2001
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
chalk, (sum
to end) and (andSandstone
so nest).
Mudstone
•
Pressure can lead to (a chem
metamorphic
Heat and (perusers)
import)
rocks such as (stale)
and (ambler.)
slate
marble
•
Some of these will melt and eventually cool as
they approach the surface to form (I ruin
vets)
intrusive
(goigneous
in use) rocks such as (get
rain.)
granite
© Boardworks Ltd 2001
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
© Boardworks Ltd 2001
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
© Boardworks Ltd 2001