Download The Nature of the earth and space

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The Nature of the earth and space
By the end of this chapter, you will be competent to...
• investigate the constituents of the atmosphere, in order to make
human affairs effective.
• contribute to maintain optimum composition of the atmosphere.
• use natural resources obtained from the earth effectively
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4.1 Main layers of the atmosphere and their features
Think of an occasion when you observed the night sky. You may have thought that
there was nothing between you and the stars. Actually, you observed the stars through
a layer made up of invisible gases which is the earth’s atmosphere.
The layer of air over the surface of the earth is called the atmosphere. It can be
considered as a protective layer which supports life. The air that we inhale is also a
part of the atmosphere. Atmosphere is mainly composed with two gases, oxygen
and nitrogen. The atmosphere extends to a height of about 1000 km above the
surface of the earth.
Do you know how the earth’s atmosphere was created? One of the theories
regarding its origin is given below;
At the time the earth was first formed, it was a ball of molten substances. This
substance was cooled down and the outer surface condensed to form a thin layer
called the crust. The inside of the earth protected by this crust is still in liquid form.
The activities within this liquid produce various types of gases. These gases that
are at extremely high temperatures can seep out through the crust, and sometimes by
volcanic eruptions. The atmosphere is formed out of the gases that were formed over
millions of years.
Fig 4.1 - Eruption of volcanoes
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Main layers of the atmosphere
Considering the nature of the atmosphere, it is composed
of five main layers. They are troposphere, stratosphere,
mesosphere, thermosphere and exosphere.
600km
Troposphere
This is the lowest layer of the atmosphere. It is about
15 km thick around the equator. Near the poles it gets
reduced to about 8 km. 90% of the total air content is
confined to this layer. Highest air pressure is found on this
layer. All of the climatic changes we experience originate at
this layer. Some examples of climatic changes that occur in
the troposphere are formation of wind, flow of wind at
various speeds in various directions, formation of clouds
and production of rain. Helicopters, parachutes and planes
fly in this layer.
Main gases in the troposphere are nitrogen and oxygen,
together with small amounts of argon, carbon dioxide, and a
few other gases. A composition of air suitable for respiration of organisms, at suitable pressures is found only in the
troposphere. Further, conditions suitable for photosynthesis
and burning are also found only in this layer.
The temperature of the troposphere reduces as we go
higher above the sea level, and at the highest level
temperature is about -44 oC.
Stratosphere
This layer found above the troposphere and stretches
up to about 50 km above sea level. The composition of the
air in this layer differs only a little from that of the troposphere. This layer contains the ozone layer which prevents
the harmful ultra-violet rays from the sun reaching the earth.
Jets fly in the lower layers of the stratosphere.
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15km
Fig 4.2 - Layers of the
atmosphere
There is a rise in the temperature as you go up the stratosphere. The ozone layer
is found here and at the highest level. Of this layer, the temperature is around +15 oC.
The reason for this is the generation of heat due to absorption of ultra violet rays.
Mesosphere
This is above the stratosphere and stretches up to about 80 km above sea level.
The lowest atmospheric temperature of -120 oC is found in this layer. The burning off
of the meteors which travel towards the earth from space begins here.
Thermosphere
The layer above the stratosphere, that is stretching
from 50 km to 600 km is called the thermosphere.
The temperature rises gradually as you go up. Since
The gases present here absorb heat radiations, the
temperature is at a higher value. Some of the radio
waves emitted from the earth get refracted back to
earth at this layer. This activity makes
communication between far distant places on earth
Fig 4.3 - Aurora
possible in a very short time. The man made satellites
too revolve round the earth in this layer, at the level
of the thermosphere. This layer too absorbs the harmful ultraviolet rays and prevent
them reaching the earth.
The ‘Aurora’ clouds which give off light at midnight visible in the polar regions
also originate at the thermosphere.
Exosphere
This is the outermost layer of the atmosophere. It is about 600 km above sea
level.
Assignment - 1
•
•
Prepare a poster showing the various layers of the atmosphere, using
suitable materials.
Exhibit it in the classroom.
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4.2 Maintaining the composition of the atmosphere at
optimum level
4.2.1 Composition of the atmosphere
The table and figure below show the composition of the atmosphere near the
surface of the earth.
Others 1%
Table 4.1- Composition of the air
Component
Nitrogen
Oxygen
Argon
Carbon dioxide
Other Gases
Percentage according
to volume
78%
21%
0.93%
0.03%
Trace
(Helium,Neon)
Water vapour
Not definite
}
1%
Oxygen
21%
Nitrogen
78%
Fig 4.4 - Composition of the air
Atmosphere is made up of a mixture of gases. The figure above shows that its
main components are oxygen and nitrogen. Carban dioxide, water and nobel gas such
as argon, neon, helium etc compose approximately 1% of the composition of air and
the composition of the water vapour varies with time and location.
All of the above components of the atmosphere are colourless and odourless.
4.2.2 Function of the atmosphere
Respiration is one of the most essential activities of organisms on earth. Oxygen
gas needed for this purpose is provided by the atmosphere. Hence, this can be
considered as the most important function of the atmosphere. In addition, there are
many other functions of the atmosphere.
Rain, wind, lightning etc occur at the lower layers of the atmosphere, this layer is
involved in the maintenance of the water cycle, which ensures the conditions needed
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for life on earth. Another function is the controlling activity of solar rays which reach
the earth as well as those which leave the earth, and thereby control the temperature of
the earth.
You already know about the protection offered by the atmosphere from the
harmful rays of the sun. The meteors from space, which can do enormous harm if they
fall on earth are also burnt off into ashes by the atmosphere.
Do you know ?
The huge crater of circumference 1.2 Km
and depth of 180 m in Winslow in Arizona is
believed to have been caused by a meteor which
fell about 50,000 years ago.
Crater in Winslow
The refraction of waves by the atmosphere also helps in radio communication
activities. This activity allows us to listen to radio services from other countries as well.
The atmosphere also helps to disperse the various gases, smoke and dust that are
discharged to the atmosphere, thus maintaining suitable conditions for survival of life.
Let us now consider the function of the different gaseous components of the
atmosphere.
Nitrogen
Under normal conditions nitrogen is a fairly inactive gas.
Many of the tissues of organisms are composed of proteins. A major component
of proteins is nitrogen. Nitrogen is essential for plant growth. The nitrogen essential for
plant growth is obtained from nitrogenous fertilisers. Atmospheric nitrogen undergoes
many chemical reactions and produce compounds which enter the plants. An initial
step in this process is the combination of nitrogen and oxygen in the presence of
lightning.
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Oxygen
Oxygen is essential for plant and animal respiration. Hence oxygen is an essential
factor for survival of life. This is the reason why persons travel into regions deficient in
oxygen have to carry their oxygen. Some such examples are deep sea divers,
mountain climbers and astronauts.
Burning of substances, decaying of dead plant and animal tissues and rusting of
metals are all activities that take place with the contribution of atmospheric oxygen.
Carbondioxide
Carbondioxide is an essential raw material for the process of photosynthesis that
takes place in plants. It helps to maintain the temperature of earth at an optimum level.
Water Vapour
Water vapour is important in maintaining the water cycle as well as the moisture
content of the earth.
4.2.3 Factors affecting the optimum composition of the
atmosphere.
Many reactions that take place in the environment help to maintain the composition
of the atmosphere at an optimum level. This helps for the well being of organisms.
Forests play a major contribution in this process. This optimum composition of the
environment may change by the addition of excess of carbon dioxide, other harmful
gases, solid and gaseous particles to the atmosphere. This condition is called
atmospheric pollution. The factors that contribute to pollution are called pollutants.
Gases such as carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen dioxide
and particles such as carbon, lead and dust are examples of some pollutants.
Human activities are mainly responsible for pollution (Fig 4.6). Some natural
phenomena too may contribute to air pollution.
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Fig 4.6 - Some human activities responsible for air pollution
Given below is a list of various components that are added to the atmosphere
which change its composition in a harmful manner.
Table 4.2
Component
How it is added
Carbon dioxide
•
Factories, vehicles, thermal power generators, houses
etc. where a large amount of fossil fuels is used to get
energy.
e.g.: Petrol, diesel, kerosine oil, coal etc.
Carbon monoxide
•
Incomplete combustion of fuels in motor engines.
Sulphur dioxide
•
Burning of coal containing a high percentage of sulphur.
Volcanic eruptions
Oxides of nitrogen
•
Combination of atmosphere nitrogen with oxygen during
lightning and in vehicle engines.
Particles of solid
and liquid wastes
e.g. carbon
particles, lead
particles, dust
•
Construction activities, activities in factories and burning
of fuel.
e.g. Cement industry, phosphate fertilizer industry,
asbestos industry
Addition of excess carbondioxide to the atmosphere causes a rise in atmospheric
temperature. It has been reported that this would result in melting of glaciers, rise of
ocean water level and change of climatic and weather patterns.
Carbon monoxide is a poisonous gas. It is harmful to organisms. It may cause
various respiratory diseases and even death at some instances.
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Gases such as sulphur dioxide, nitrogen dioxide dissolve in rain water and produce
an acidity in the rain water. This condition is known as acid rain. Acid rain causes harm
to organisms, water bodies and to buildings.
The particulate pollutants cause respiratory diseases. The increase of such diseases
at present is basically due to the increase of pollutant particles in the atmosphere.
Another harmful result is the reduction of the transparency of the atmosphere.
4.2.4 Maintaining the composition of the atmosphere at an optimum level.
If we can control the addition of the above harmful substances to the atmosphere,
we can maintain the levels of each constituents at an optimum level. Some strategies
for such an action are stated below;
1. Preventing destruction of forests and taking steps for re-forestation. (Fig 4.8)
2. Minimize the use of fossil fuels as much as possible.
e.g. use public transport instead of private vehicles.
3. Use energy sources that emit minimum amount of harmful substances to the
environment.
Example: Hydro power, wind power, tidal power.
4. Use fossil fuel free of harmful substances.
e.g. Sulphur free coal, lead free petrol.
5. Removing harmful substances from factory effluent before they are
released to the atmosphere. (Fig. 4.7)
6. Recycling of garbage instead of burning those.
Fig 4.8 - Re forestation
Fig 4.7 - Smoke tower directed high
into the air
Assignment - 2
Make a list of activites, your family members and you can do to control addition of harmful substances to the environment.
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4.3 Natural resources from the earth
4.3.1 Minerals and rocks
Observe a newly broken piece of granite and quartz. (Better observations can be
made using a hand lens) You can notice that there are different coloured parts in the
piece of granite, while the quartz is even in colour. Did you observe that there is a
resemblance between some parts of the piece of granite and the quartz?
Fig 4.9 - Granite
Fig 4.10 - Quartz
A substance which exists as a solid and is made up of one type of element or
a single compound is known as a mineral. Quartz is a mineral made up of a single
compound. Diamond, graphite, gold silver and sulpher are minerals made up of
elements. A mineral is a substance in crystal form which has a definite composition
and composed with one type of element or a single compound.
Diamond
Gold
Graphite
Fig 4.11 - Minerals made up of elements
A piece of granite is made up of a mixture of three different types of minerals. A
solid substance made up of a number of minerals is called a rock. Therefore, granite is
an example for a rock. It is a mixture of feldspar, quartz and mica.
Granite taken from different places will have different percentages of mineral
components. Therefore their colours will be different. This observation suggests the
composition of rocks may differ from place to place. However, the composition of
minerals do not change according to the location, because a mineral consists of a
single pure substance.
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Table 4.3 shows a comparison between rocks and minerals.
Table 4.3
Minerals
•
•
•
Pure substance
Homogenous
Fixed composition
Rock
•
•
•
Mixture of two or more pure substances.
Heterogeneous
Composition varies
4.3.2 Minerals and rocks of Sri Lanka.
Sri Lanka is rich in minerals. These minerals and rocks are used in a variety of
industries. Some minerals are also exported. Let us learn more about some rocks and
minerals found in Sri Lanka.
Fig 4.12 - Limestone
Limestone
:
Apatite
:
Iron ore
:
Mineral sands:
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Fig 4.13 - Apatite
Fig 4.14 - Iron ore (Heamotite)
Limestone is abundantly found in areas such as Puttalam,
Kankasanthurai, Matale and the southern coast of the island.
Limestone is used as a raw material in manufacturing cement and
in the lime industry and manufacturing toothpaste.
The Eppawela area has a large ore of apatite. It is used to produce
phosphate fertiliser. Finely crushed apatite can be used directly as
a fertiliser for long term crops such as tea, rubber and coconut.
Apatite has a low water solubility. Therefore it is essential to
increase the solubility, if it is used for short term crops. There are
various chemical methods to improve its solubility.
All containing iron are called iron ores. Iron is manufactured using
iron ores. eg. haemotite magnetite. Various types of iron ores are
found in Seruwila, Kahawatta, Kalawana and Rakwana.
Mineral sands are commonly found in some coastal areas of Sri
Lanka, Black coloured Illemenite is found in northern beaches
such as Pulmudai. In Hambantota and Tangalle areas a red
coloured mineral sand garnet is common. Some common types of
mineral sands and their uses are stated in the table below. (Table 4.4)
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Table 4.4 - Some mineral sands and their uses
Type of mineral sand
Illemenite
Rutile
Zircon
Monosite
Clay
:
Use
For production of paints, titanium metal for aero plane parts.
For production of paints, Welding rods.
Production of crockery, Porcelain items.
Polishing of lenses, production of gas mantles.
Clay is formed by the weathering of rock. Many kinds of clay are
found in different parts of Sri Lanka. When clay is mixed with water it
can be moulded into many shapes. This property of clay is called plasticity.
Ordinary clay is suitable for manufacturing tiles and bricks. Clays with
special properties are used for other types of productions. Different types
of clay and their uses are given in table 4.5.
Fig 4.15 - Ordinary Clay
Fig 4.16 - Kaolin
Table 4.5 - Various types of clay, their properties and uses
Type of clay
Kaolin
Properties
White when burnt.
Resistant to high temperature.
Plasticity is less.
Uses
Production of porcelain
Ball clay
Grey in colour. Hard.
High Plasticity
Crockery, ornaments.
Fire clay
Ordinary clay
Resistant to high temperature.
Production of hearths,
Tiles, bricks and pots etc.
Very fine. Red when burnt.
Assignment - 3
Indicate the distribution of various kinds of minerals and rocks in a map of
Sri Lanka in a creative manner.
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Fig 4.17 - Ornaments made out of clay
Excercise
1
Select suitable words from those within brackets and fill the blanks in the
following paragraph.
(atmosphere, nitrogen, troposphere, covering, layers, ultra violet rays oxygen,
ozone, heat, meso, exo)
Note : some words may be used more than once.
The ……………….. on the earths ……………… acts as a layer for protecting
organisms. In this the layer closest to the earth is known as the …………....…….
. The main components in it are ………………. and ……………. .
……...…….. sphere is found outside the ………………. sphere. The
……………… sphere that prevents harmful rays from the sun reaching the earth
is found here. The …………. sphere where the lowest temperatures are recorded
is found outside this layer as ……....…. and ………........... in order.
2. Prepare an article for a science magazine describing the ill effects that will have to
be faced by man if the atmosphere is not available.
3. Describe the way you would try to identify rocks from minerals by observing
through the naked eye or through a hand lense.
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