© Boardworks Ltd 2003 KS4 Changes to the Earth and atmosphere

© Boardworks Ltd 2003

KS4 Changes to the Earth

and atmosphere


The Atmosphere


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


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


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


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


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


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


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


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


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


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




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?


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.


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


The Earth’s Structure


The Earth’s Structure

Beneath the atmosphere the Earth consists of 3 main layers:


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.


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


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

%


• 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?


Atmosphere

Outer core

Crust

Mantle

Inner core

Attach labels to the correct part of the diagram.


Plate Tectonics


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.



Sea floor spreading

When two oceanic plates move apart molten rock rises to the surface.

magma rising

sea floor spreading

oceanic plate


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


Continental Drift


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


Plate boundaries


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)


• 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


Rocks


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.


Igneous rocks

• These are rocks formed by the cooling of molten rock (magma.)

magma

volcanoMagma cools and solidifies forming igneous rocks.


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.


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.


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.


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


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


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


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


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


The rock cycle


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


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


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


What gas protects us against dangerous UV radiation?

1. Sulphur dioxide

2. Nitrogen oxide

3. Methane

4. Ozone


What gas is a major cause of the greenhouse effect?

1. Sulphur dioxide

2. Nitrogen oxide

3. Carbon dioxide

4. Chlorine dioxide


What process increases atmospheric carbon dioxide levels?

1. Photosynthesis

2. Respiration

3. Formation of Fossil fules

4. Formation of carbonate rocks


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


What layer of the Earth is mostly molten iron and nickel?

1. Inner core

2. Outer core

3. Mantle

4. Crust


What layer of the Earth is made of viscous semi-molten magma?

1.Inner core

2.Outer core

3.Mantle

4.Crust


What type of rock is formed by solidification of molten magma?

1. Igneous

2. Metamorphic

3. Sedimentary

4. Fossilised


What type of rock is formed by cementation of small particles of weathered rock?

1. Igneous

2. Metamorphic

3. Sedimentary

4. Fossilised


What type of rock is formed by the effect of heat and pressure upon other rocks?

1. Igneous

2. Metamorphic

3. Sedimentary

4. Fossilised


What type of rock is least likely to contain fossils?

1. Igneous

2. Metamorphic

3. Sedimentary

4. Fossilised


What is the process where tectonic plates separate and magma creates new solid crust?

1. Weathering

2. Ageing

3. Sea floor spreading

4. Sedimentation


What is the process where tectonic plates move gradually apart?

1. Continental breakfast

2. Continental drift

3. The rock cycle

4. Subduction


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

Documents

© Boardworks Ltd 2003 KS4 Changes to the Earth and atmosphere