© boardworks ltd 2005 1 of 48 ks4 chemistry earth and atmosphere

© Boardworks Ltd 20051 of 48

KS4 Chemistry

Earth and Atmosphere



The Earth’s structure

Plate tectonics

Development of the atmosphere

Rocks

O3 and CO2

Summary activities

Contents


• The Earth was formed about 4,500 million years ago.

• 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 have also been present.

• This is rather like the atmosphere on Mars and Venus today.

• The water vapour condensed to form the oceans.

Mars

Venus

The early atmosphere


• Carbon dioxide reacted with rocks and much became trapped in them.

• 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.

Earth

Photosynthesis increased

oxygen levels

Oxygen levels increase


• 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.

Nitrogen appears

78%

21% 1%

Nitrogen

Oxygen

Other


Copy the timeline and arrange the blue boxes in appropriate places along the line.

4,500 million

Now3,000 million

2,000 million

1,000 million

500 million

200 million

No gases

H2 and He

CO2 NH3 CH4

H2O N2 O2

Volcanoes

Algae

Plants

Atmosphere timeline


All positions are approximate

4,500 million

Now3,000 million

2,000 million

1,000 million

500 million

200 million

No gases

H2 and He

Volcanoes Algae Plants

CO2 NH3 CH4

O2 N2 H2O

Timeline answers


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%5,000 3,000 0

Com

posi

tion

perc

enta

ge

Time (millions of years)

now

Approx 4,000M

Approx 3,300M

Approx 2,000M

Changing gas levels




Plate tectonics


Rocks

O3 and CO2

Summary activities

Contents


• 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

Ozone: a vital filter


The carbon cycle


CO2 release or consumption?


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?

Carbon dioxide and temperature


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.

Changing CO2 concentrations


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.

This means that 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

The greenhouse effect




Plate tectonics


Rocks

O3 and CO2

Summary activities

Contents


Beneath the atmosphere the Earth consists of 3 main layers:



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.

5,500 C

1,110 km

3,000 km

1,300 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 core


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

2,900km

The mantle


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

%

The crust


• I’m a viscous semi-solid withconvection currents circulating in me.

• I’m iron and nickel too, but I’m liquid.

• I just hang around on the outside.

• I’m really very thin and am mostlysilicon, oxygen and aluminium.

• I am dense, very hot, made mostly ofsolid iron and nickel.

Inner core

Outer core

Atmosphere

Crust

Mantle

What am I?


Atmosphere

Outer core

Crust

Mantle

Inner core

Sections of the Earth




Plate tectonics


Rocks

O3 and CO2

Summary activities

Contents


• 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 a year this can have huge effects over long periods of time.

Tectonic plates


Why do plates move?


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

magma rising

sea floor spreading

oceanic plate

Sea floor spreading


Pangaea• 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 asuper-continent called Pangaea.

• Over millions of years they have drifted to their present positions on the floating tectonic plates.

Millions of years

Continental drift


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!

Jigsaw fit

Similar rocks and fossils

Evidence for continental drift


Plate boundaries


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

Effects at plate boundaries

• the continental plate buckles upwards while the oceanic plate subducts (goes underground)

• volcanoes result from the rising magma (melted oceanic plate)




Plate tectonics


Rocks

O3 and CO2

Summary activities

Contents


There are three main types of rocks:

IgneousIgneous – formed when molten rock cools.

SedimentarySedimentary – formed by the “cementing together” of small grains of sediment.

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.

Types of rocks


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

magma

volcanoMagma cools and solidifies forming igneous rocks.

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.

Types of igneous rocks


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.

Igneous rocks and crystal size


• 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.

Chemical and physical weathering


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.

Types of 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 and 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. 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.

Types of 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

What’s the rock?


The rock cycle




Plate tectonics


Rocks

O3 and CO2

Summary activities

Contents


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.


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.


Anagrams


Multiple-choice quiz

© boardworks ltd 2005 1 of 48 ks4 chemistry earth and atmosphere

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