© boardworks ltd 2003 ks4 changes to the earth and atmosphere
TRANSCRIPT
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KS4 Changes to the Earth
and atmosphere
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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 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.
Saturn
Jupiter
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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.
78%
21% 1%
Nitrogen
Oxygen
Other
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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 2O3
Oxygen ozone
Earth
Harmful UV rays stopped
with ozone layer
Harmful UV rays reach Earth’s surface
without ozone layer
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Copy the timeline and arrange the blue boxes in appropriate places along the line.
4500 million
Now3000 million
2000 million
1000 million
500 million
200 million
No gases
H2 and He
CO2 NH3 CH4
H2O N2 O2
Volcanoes
Algae
Plants
Activity
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All positions are approximate
4500 million
Now3000 million
2000 million
1000 million
500 million
200 million
No gases
H2 and He
Volcanoes Algae Plants
CO2 NH3 CH4
O2 N2 H2O
Answer
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1. What was the main gas in the atmosphere around 3500M years ago?
2. Where did this gas come from?
3. What process led to reduction in CO2 levels?
4. What gas protects life from harmful UV radiation?
5. What % of the present atmosphere is oxygen?
Carbon dioxide
Volcanoes
Photosynthesis
Ozone
21%
Activity
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Use the graph to estimate the answers.
1.How long ago was the atmosphere 75% CO2?
2.How long ago were the CO2 and N2 levels in the atmosphere equal?
3.How long ago was the atmosphere 50% nitrogen?
carbondioxide
nitrogen
oxygen
100%
50%
0%5000 3000 0
Com
posi
tion
perc
enta
ge
Time (millions of years)
now
Approx 4,000M
Approx 3,300M
Approx 2,000M
Activity
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Find the words in the word-searchWrite a sentence about how each has played a part in the evolution of the Earth’s atmosphere.
P Z K P A G T U N A T G N R ED H J F N E L N J M M E V D QE E O X Y G E N R M G A I Z RC L I T O G F M T O W X U V XO I Q W O Z K I R N O V M P WI U E R T S O D O I K W Y V KT M T M Q C Y N D A I O B K OR I M E T H A N E K J B N M NN O Q Y X C O S T J Q Z E W ZA J X Z L B M E W H S V L W BF W Z O R U X U Z Y E W F R PV M V A Q Q Y Y Q W B S J D IQ B C H L G O O P M R T I R PM B B K C R T E E X E H H S K
Ammonia
Carbon dioxide
Helium
Hydrogen
Methane
Nitrogen
Oxygen
Ozone
Photosynthesis
Volcano
Activity
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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
Carbon Dioxide (ppm)
1979 333.681980 335.551981 337.141982 338.381983 340.251984 341.821985 343.181986 344.261987 345.991988 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.
Which label goes with each picture?
200ppmCO2
300ppmCO2
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.
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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!
Earth
Heat from sun
Heat loss
More CO2
Earth
Heat from sun
Heat loss
hotterAnd hotterAnd hotter!
balanced same temp
Greenhouse effect
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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 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
1110 km
3000 km
1300 km
Outer coreInner 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.
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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.
Mantle
2900km
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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.
Crust
20-60 km
05
101520253035404550
O Si Al Fe Ca Na K Mg
%
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• I am dense, very hot, made mostly of solid iron and nickel.
• I’m iron and nickel too, but I’m liquid.
• I’m really very thin and am mostly silicon, oxygen and aluminium
• I’m a viscous semi-solid with convection currents circulating in me.
• I just hang around on the outside. Atmosphere
Outer core
Crust
Mantle
Inner core
What am I?
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Atmosphere
Outer core
Crust
Mantle
Inner core
Attach labels to the correct part of the diagram.
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Plate Tectonics
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Tectonic plates
• The crust is made of about twelve platesplates.• 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.
magma rising
sea floor spreading
oceanic plate
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Pangaea
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.
• Over millions of years they have drifted to their present positions on the floating tectonic plates.
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
volcanoes result from the rising magma (melted oceanic plate)
volcano
continental plate
oceanic plate
magma rising
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)
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• 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
K G F N Z P D C L EL F O Q A P C X K EE M S V O L C A N OI X S U B D U C T AD R I F T Q J S M WM K L Q H S I A W FP L A T E S G K E NZ V R Q A M S P F XP A N G A E A P V AE V R A D G W L I S
Activity
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Rocks
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Types of rocks
There are three main types of rocks:
1.1.IgneousIgneous - formed when molten rock cools.
2.2.SedimentarySedimentary – formed by the “cementing together” of small grains of sediment.
3.3.MetamorphicMetamorphic – 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
volcanoMagma cools and solidifies forming igneous rocks.
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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.
Extrusive igneous rocks, like basalt, have crystals that are usually small.
Intrusive igneous rocks that cool really slowly can have very big crystals.
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 are rocks formed when particles of sediment build up and are “cemented together” by the effect of pressure and minerals.
sea
Fragments washed to the sea
Sedimentary rocks
Rocks are brokenup by the actionof weather
Sedimentary rocks
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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.
Gettin
g o
lder
Sandstone is formed from the cementing together of grains of sand.
Sedimentary rocks
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Magma
metamorphicrock
forminghere
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.
heat
Pressure from surface rocks
Metamorphic rocks
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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.
Metamorphic rocks
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Match the rock with the correct description.Give an example of this type of rock.
Rock typeRock type DescriptionDescription
intrusive igneous
Large crystals, hard rock
metamorphic Sandy texture, soft rock
extrusive igneous
Small crystals, hard rock
sedimentary Wavy layers of crystals
Activity
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The rock cycle
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Crack the code! What should this really say?
• (Giant hewer) leads to fragments collecting in the sea and forming (am seen dirty) rocks such as chalk, (sum to end) and (and so nest).
• Heat and (perusers) can lead to (a chem import) rocks such as (stale) and (ambler).
• Some of these will melt and eventually cool as they approach the surface to form (I ruin vets) (go in use) rocks such as (get rain).
Weathering
sedimentary
mudstone sandstone
pressure metamorphic
slate marble
intrusive
igneous granite
Activity
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What gases would have formed the original atmosphere around planet Earth?
1. Hydrogen and helium
2. Oxygen and nitrogen
3. Methane and ammonia
4. Carbon dioxide and water
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What gases form the majority of the present atmosphere around planet Earth?
1. Hydrogen and helium
2. Oxygen and nitrogen
3. Methane and ammonia
4. Carbon dioxide and water
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What gas protects us against dangerous UV radiation?
1. Sulphur dioxide
2. Nitrogen oxide
3. Methane
4. Ozone
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What gas is a major cause of the greenhouse effect?
1. Sulphur dioxide
2. Nitrogen oxide
3. Carbon dioxide
4. Chlorine dioxide
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What process increases atmospheric carbon dioxide levels?
1. Photosynthesis
2. Respiration
3. Formation of Fossil fules
4. Formation of carbonate rocks
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What layer of the Earth is around 50Km thick and high in silicon and oxygen?
1. Inner core
2. Outer core
3. Mantle
4. Crust
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What layer of the Earth is mostly molten iron and nickel?
1. Inner core
2. Outer core
3. Mantle
4. 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. Igneous
2. Metamorphic
3. Sedimentary
4. Fossilised
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What type of rock is formed by cementation of small particles of weathered rock?
1. Igneous
2. Metamorphic
3. Sedimentary
4. Fossilised
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What type of rock is formed by the effect of heat and pressure upon other rocks?
1. Igneous
2. Metamorphic
3. Sedimentary
4. Fossilised
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What type of rock is least likely to contain fossils?
1. Igneous
2. Metamorphic
3. Sedimentary
4. Fossilised
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What is the process where tectonic plates separate and magma creates new solid crust?
1. Weathering
2. Ageing
3. Sea floor spreading
4. Sedimentation
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What is the process where tectonic plates move gradually apart?
1. Continental breakfast
2. Continental drift
3. The rock cycle
4. Subduction
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Which of these is notnot evidence for continental drift theories?
1. Similarities of fossils
2. Similarities of rock layers
3. Jig-saw fit of coastal shapes
4. Similarities of climate