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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