Earth

Materials

Dr. E. Kruiswijk

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Limestone

Limestone is one form of calcium carbonate, the others being chalk and

marble. Limestone is taken from the ground by quarrying and can be used

in building stone. Many buildings including the Welsh National museum in

Cardiff are made of this material. It can be used where ornate carving

and statues are needed. Powdered limestone is added to soils and lakes to

neutralise acid caused by acid rain but much of the rock is heated in a

rotary kiln to form calcium oxide or quicklime.

CaCO3 CaO + CO2

When quicklime is added to water an exothermic reaction occurs and the

lime is converted into slaked lime or calcium hydroxide.

CaO + H2O Ca(OH)2

This is called agricultural lime and again is used to neutralise acid soils.

Cement

This is made by adding powdered lime and clay in a rotary kiln and heated

until a light grey powder is formed. This can be mixed with sand water to

form cement which is used to bind bricks together. If additional rock in

the form of gravel is added concrete is produced. Both these products

undergo a slow chemical reaction after water has been added which

hardens the powder into a stone like material.

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Glass

When limestone sand and soda (sodium carbonate) is heated a very

viscous liquid called glass is formed.

Rocks Types and Formation

Sedimentary rocks are made from existing rocks over millions of years at

the bottom of seas and oceans as layers of sediment are deposited on top

of one another. The sheer weight of the rock squeezes out the water and

salts from the water crystallise out to act as the cementing agent. When

much of the sediment is composed of shells then the rock formed will be

limestone. If the sediment is mainly formed of fine sand grains then

sandstone is formed. Sedimentary rocks contain fossils which were

formed from dead animals and plants that were trapped in the sediment

as it fell to the bottom. Fossils can be used to identify rocks age from

different places and to identify rocks which are younger than others.

Igneous Rocks

In general these rocks are composed of interlocking crystals which

contain different minerals and are-likely to be different colours.

Extrusive igneous rocks

Igneous rocks are formed from the molten rock from the mantle of the

earth which is called magma. If the magma comes to the surface it is

called lava. When the lava erupts it forms the structure called a volcano

the material formed when it cools is extrusive igneous rock. The rock is

composed of small crystals as the lava has cooled quickly. An example of

this is basalt, figure 1.

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Figure 1: Basalt.

Intrusive igneous rocks

When this magma fails to reach the surface it solidifies within the

Earth's crust and it is called intrusive. The slower the magma cools the

larger the crystals in the rock. An example of this is granite, figure 2.

Figure 2: Granite.

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Metamorphic Rocks

These are formed when pre-existing rocks are exposed to high

temperatures and pressures often associated with processes such as

mountain building. Earth movements in the crust are often called tectonic

activity and can cause all types of rocks to be buried deep underground.

Here the rocks are compressed and heated. This can change the texture

and mineral structure of the rock without melting it back to magma. Two

examples of this are slate which is formed from mud stone and marble

which is formed from limestone. This type of rock is often banded

because of the bands of interlocking crystals e.g. Schist, figure 3.

Figure 3: Schist.

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The Rock cycle

Figure 4: The Rock cycle.

The structure of the Earth

Figure 5: The structure of the Earth.

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The Earth is nearly spherical and has a layered structure comprising

• a thin crust;

• an extremely viscous mantle, extending almost halfway to Earth's

centre;

• a core, with just over half of the Earth's radius, made of nickel and

iron the outer part of which is liquid and the inner part of which is solid.

The overall density of the Earth, figure 5, is much greater than the mean

densities of the rocks which form the crust. This indicates that the

interior of the Earth is made of material different from and denser than

that of the crust.

The geological time scale

Mountains are being continually worn away by erosion and weathering and

it is this material that form new rocks. Younger sedimentary rock lie on

the top of older rocks as they made afterwards. These sedimentary rock

layers can be tilted, folded, fractured and sometimes turned upside down

by large forces which push and pull the unstable crust. Slowly over

millions of years this cause mountains to form.

The changing face of the Earth

It was thought that the features were the result of the shrinking of the

crust as the Earth cooled down following its formation but new evidence

from the location of volcanic activity (ring of fire and mid Atlantic ridge)

have shown that the crust is cracked into a number of large pieces

(tectonic plates) which are constantly moving at relative speeds of a few

centimetres per year as a result of convection currents within the

Earth's mantle driven by heat released by natural radioactive processes.

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This movement has caused the continents to move relative to one another

from a single land mass to the present continents. The evidence for this

is:

• have shapes which fit closely

• have similar patterns of rocks and fossils

There are three different fossil fuels namely Oil, Natural gas and Coal.

These are non renewable fuels as they can not be made again in our

lifetime.

Oil Formation

Millions of years ago the seas were warm and teemed with marine animals

and plants. When they died they formed a thick layer on the sea bed.

Over millions of years, layer upon layer of sediment covered the remains

of the animals and plants. The weight of the sediment caused huge

pressures and because there was no oxygen the organic material only

partly decayed. At these high pressures and temperature oil was formed.

The sediments slowly changed to rock and were folded by Earth

movements. The oil and gas moved through some layers of rock until they

met harder, impervious rock through which they could not pass, figure 6.

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Figure 6: Formation of oil.

Oil Recovery

The oil can be removed by drilling through the non porous rock until the

oil rich areas are found. The oil can then be pumped, figure 7, to the

surface and used.

Figure 7: Oil drilling tower.

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Crude oil

This is a mixture (not chemically combined together) of a very large

number of organic (carbon) compounds. To make crude oil more useful it is

separated by physical means. As the boiling points of the compounds are

similar we need to use fractional distillation, figure 8.

In the laboratory In the Refinery

Figure 8: Crude oil distillation.

The many hydrocarbons (compounds that contain carbon and hydrogen) in

oil may be separated into fractions by evaporating and then condensing at

different temperatures each of which contains molecules with a similar

number of carbon atoms.

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The hydrocarbons in crude oil and their uses

The larger the molecules (the greater the number of carbon atoms) in a

hydrocarbon:

• the higher its boiling point;

• the less volatile it is;

• the less easily it flows (the more viscous it is);

• the less easily it ignites (the less flammable it is).

Figure 9: Barrel of crude oil.

This limits the fuels to smaller molecules. The larger molecules have to be

broken apart or cracked to form smaller molecules.

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The process of cracking

Larger molecules in crude oil are cracked into smaller molecules, using

heat and a catalyst. These smaller molecules can be used as fuels or for

making plastics such as polyethene (use plastic bags bowls and buckets) or

PVC (use pipes electrical insulation)

C16H34 C9H20 + +heat

catalyst

Figure 10: Cracking

The Earth's atmosphere

The composition of the air has not changed for 200 million years, 4/5

nitrogen, 1/5 oxygen and small amounts of carbon dioxide and water

vapour and noble gases (argon), figure 11.

Figure 11: Composition of air.

Burning fuels produces new compounds most of which are gases alters the

composition of the air. The main reaction occurs when the elements from

compounds react with oxygen and produces compounds called oxides

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(oxidation) e.g.:

Sulphur + Oxygen Sulphur Dioxide

Carbon + Oxygen Carbon Dioxide

Hydrogen + Oxygen water (vapour)

In cars where temperatures are much higher un-reactive nitrogen is also

converted into nitrogen oxides.

Nitrogen + Oxygen Nitrogen Dioxide

Global warming

The Earth's atmosphere is warming up because increased level of carbon

dioxide (greenhouse gas) traps sunlight and converts the energy to heat

rather than it being reflected from the Earth's surface back into space.

Acid rain

The sulphur dioxide and nitrogen oxides which are produced when fuels

are burned in furnaces and engines can harm plants and animals directly.

These oxides dissolve in rain and make it more acidic. If the water in

rivers and lakes becomes too acidic, plants and animals cannot survive.

Acidic fumes and acidic rain also damage the stonework and metalwork on

buildings.

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Homework exercises

1)a Give three forms of calcium carbonate?

b How is limestone removed from the ground?

c Give three problems associated with quarrying?

d Give 2 uses of limestone?

e What is quicklime and what is it use for?

f How is cement made?

g How is glass made?

h What are sedimentary rocks and how are they formed?

i How are fossils formed?

j How are rocks identified?

2)a Where do igneous rocks come from?

b It the rock appears at the surface what is it called and give an

example?

c What structures appear with this type of rock?

d What type of crystals form at the surface?

e How is granite formed?

f What type of crystals form when granite solidifies and why?

g What are metamorphic rocks?

h What processes are they associated with?

i What makes igneous rock speckled in colour?

j Name an igneous rock found in the bathroom?

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3)a Give examples of metamorphic rocks and what they are made of?

b Draw a simple rock cycle?

4)a What shape is the Earth?

b Draw a diagram to show its structure.

c What is the mantle like?

d What is the core made of?

e How are mountains worn away?

f What can happen to sedimentary rocks once they are formed?

g Where do find the oldest rocks?

h How is the Earth's crust arranged?

i What are these called? What evidence do we have for their existence

5)a What is required to start oil formation?

b How long does it take oil to form?

c What must be absent for oil to form?

d What two other conditions are required for oil formation?

e How is oil recovered from the ground?

f Name 3 fossil fuels?

g Why are they said to be non renewable fuels?

h What stops the oil leaking out of the ground?

i What does the word folded mean?

j What does the term partially decayed mean?

6)a Draw diagrams to show distillation of oil in the laboratory and the

refinery.

b Explain how distillation works?

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7)a How do the properties of hydrocarbons change as the number of

carbons increase?

b Why does this limit hydrocarbons for use as fuels?

c What does cracking do?

d Why is cracking important?

e What are the products' of cracking?

8)a Give the composition of the Earth's atmosphere?

b What are the two products of burning hydrocarbons?

c What is the greenhouse effect?

d What is acid rain?

e What damage is caused by acid rain?

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The rest of the material only needs to be learnt if you are

sitting the higher paper.

Tectonic plates

• may slide past each other. This is happening along the Californian coast

giving rise to earthquakes;

• may move towards each other. As this happens, the thinner, denser

oceanic plate is driven down (sub-ducted) beneath the thicker granitic

continental plate where it eventually melts. The continental crust is

forced upwards. Earthquakes are produced and magma may rise through

the continental crust to form volcanoes. This is happening along the

western side of South America (the Andes);

• may move apart from each other. Magma rises to fill the gap and

produces new, basaltic, oceanic crust. This is known as sea floor spreading

and is happening along oceanic ridges, including the mid-Atlantic ridge.

The iron-rich minerals in the magma record the direction of the Earth's

magnetic field at the time when the rising magma solidified. Magnetic

reversal patterns in oceanic crust occur in stripes parallel to oceanic

ridges, matching the periodic reversals of the Earth's magnetic field and

so supporting the concept of sea floor spreading.

The Earth's Atmosphere the first billion years.

During the early years of the Earth much volcanic activity was present

and most of the gas came from this source. Most of the gas would have

been carbon dioxide water vapour with small amounts of methane and

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ammonia with little or no oxygen (like Mar and Venus). When plants

evolved and covered most of the earth

• The atmosphere gradually became more and more “polluted” with

oxygen. This meant that there were very few places where micro-

organisms which could not tolerate oxygen could live;

• most of the carbon from the carbon dioxide in the air gradually became

locked up in sedimentary rocks as carbonates and fossil fuels;

• the methane and ammonia in the atmosphere reacted with the oxygen;

• nitrogen gas was released into the air, partly from the reaction between

oxygen and ammonia, but mainly from living organisms, including

denitrifying bacteria;

• this oxygen in the atmosphere resulted in the development of an ozone

layer. This filters out harmful ultraviolet radiation from the Sun allowing

the evolution of new living organisms.

Carbonate rocks are sometimes moved deep into the Earth by geological

activity. They may then release carbon dioxide back into the atmosphere

via volcanoes.

Change in the carbon cycle

The release of carbon dioxide by burning the carbon locked up over

hundreds of millions of years in fossil fuels increases the level of carbon

dioxide in the atmosphere. Though the reaction between carbon dioxide

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and sea-water also increases, producing insoluble (mainly calcium)

carbonates which are deposited as sediment and soluble

hydrogencarbonates (mainly calcium and magnesium); this does not wholly

absorb the additional carbon dioxide released into the atmosphere, figure

12.

Figure 12: The Greenhouse effect.

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Naming Organic Compounds

Alkanes

These are said to be saturated as they do not contain any double bonds.

Alkanes are used mainly as fuels.

C

H

H

H

H

H

C C

H

H

H

H

H

H

C C

H

C

H

H

H

H

H

H

Methane ethane propane

Figure 13: Alkanes

Alkenes

C C

H

H H

H

These are unsaturated (contain a double bond). These unsaturated

hydrocarbons are reactive and so are useful to make other substances

including polymers. Polymers are very large molecules and are formed

when many small molecules, called monomers join together. This is called

polymerisation. Plastics are polymers e.g. ethane.

C C

H

H H

H

n C C

H

H H

H n

Figure 14: Polymerisation.

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Higher Level Paper only

11)a Where do you get side slippage of tectonic plates?

b What happens when two tectonic plates collide?

c What happens when two plates move apart?

d What was different about the Earth's atmosphere a millions years ago?

e What effect did plants have on the Earth's atmosphere?

12)a Why did most of the carbon dioxide disappear?

b What was the fate of the ammonia and methane?

c What gas was released into the atmosphere and where did it originate

from?

d What was the effect of oxygen being present in the atmosphere and

why was it important for evolution?

e What is the greenhouse effect and why might it be a problem in the

near future?

13)a Draw diagrams to show ethane, ethene, methane and propane

b What do the terms saturated and unsaturated mean?

c What is the main use for unsaturated hydrocarbons?

d Write an equation for the polymerisation of ethene

e Draw displayed formula for polythene

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