Ozone Depletion:

Ozone:
Ozone is a highly reactive and unstable gas, which is formed by the recombination of oxygen (O2) atoms in the presence of intense radiation. Its symbol is O3.

Ozone Layer:
The ozone layer is a naturally occurring zone found in the stratosphere, situated between 10-15 kms above the surface of the Earth. The main function of the ozone layer is to act as a shield against ultraviolet (UV) radiations from the Sun because these rays are harmful to life.

Ozone Depletion:
Destruction of the stratospheric ozone layer which shields the earth from ultraviolet radiation harmful to life. ...

Causes Of Ozone Layer Depletion:
The Main Ozone-Depleting Substances (ODS)
• Chlorofluorocarbons (CFCs)
• The most widely used ODS, accounting for over 80% of total stratospheric ozone depletion.
• Used as coolants in refrigerators, freezers and air conditioners in buildings and cars manufactured before 1995.
• Found in industrial solvents, dry-cleaning agents and hospital sterilants.
• Also used in foam products — such as soft-foam padding (e.g. cushions and mattresses) and rigid foam (e.g. home insulation).
• Halons
• Used in some fire extinguishers, in cases where materials and equipment would be destroyed by water or other fire extinguisher chemicals. In B.C., halons cause greater damage to the ozone layer than do CFCs from automobile air conditioners.
• Methyl Chloroform
• Used mainly in industry — for vapour degreasing, some aerosols, cold cleaning, adhesives and chemical processing.
• Carbon Tetrachloride
• Used in solvents and some fire extinguishers.
• Hydro fluorocarbons (HCFCs)
• HCFCs have become major, “transitional” substitutes for CFCs. They are much less harmful to stratospheric ozone than CFCs are. But HCFCs they still cause some ozone destruction and are potent greenhouse gases.

OR

The cause of ozone depletion is the increase in the level of free radicals such as hydroxyl radicals, nitric oxide radicals and atomic chlorine and bromine. The most important compound, which accounts for almost 80% of the total depletion of ozone in the stratosphere are chlorofluorocarbons (CFC). These compounds are very stable in the lower atmosphere of the Earth, but in the stratosphere, they break down to release a free chlorine atom due to ultraviolet radiation. A free chlorine atom reacts with an ozone molecule (O3) and forms chlorine monoxide (ClO) and a molecule of oxygen. Now chlorine monoxide reacts with an ozone molecule to form a chlorine atom and two molecules of oxygen. The free chlorine molecule again reacts with ozone to form chlorine monoxide. The process continues and the result is the reduction or depletion of ozone in the stratosphere.

Effects Of Ozone Depletion
Following are the major effects of ozone layer depletion.
i) It will increase the risk of skin cancer
ii) It has resulted in melanomas, a kind of tumour.
iii) It greatly affects eyes and produces disease of vision.
iv) It suppresses immunity system of human beings.
v) UV rays damage various crops.
vi) It kills plankton and fish larvae.
vii) It causes sunburn in human beings.
viii) It causes spotting of leaves in plants and trees, thus decreases productivity of the plants.

Acid Rain:

“The rainwater which contains a large amount of poisonous acids like sulphuric acid, sulphurous acid, nitrous acid and other pollutants is known as the Acid Rain.”

Formation of Acid Rain
Acid rain is caused by a chemical reaction that begins when compounds like sulphur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain. Sulphur dioxide and nitrogen oxides dissolve very easily in water and can be carried very far by the wind. As a result, the two compounds can travel long distances where they become part of the rain, sleet, snow, and fog that we experience on certain days.

Causes Of Acid Rain:
Human activities are the main cause of acid rain. Over the past few decades, humans have released so many different chemicals into the air that they have changed the mix of gases in the atmosphere. Power plants release the majority of sulphur dioxide and much of the nitrogen oxides when they burn fossil fuels, such as coal, to produce electricity. In addition, the exhaust from cars, trucks, and buses releases nitrogen oxides and sulphur dioxide into the air. These pollutants cause acid rain.

OR

The main causes of acid rain are…
Natural Sources:
• Lightning strikes (cause nitrogen molecules to be oxidized)
• Combustion of hydrogen sulphide (hydrogen sulphide is formed from the breakdown of sulphates in organic matter in the absence of oxygen- anaerobic conditions). This reaction forms sulphur dioxide.

Human Sources:
• Combustion engines (car, airplanes etc.)
• Burning of fossil fuels and coal
• Some mineral ores contain sulphur dioxide, and this is released when the minerals are processed.

Effect Of Acid Rain:
i) Kills flora and fauna
ii) Damages the buildings
iii) Causes skin cancer
iv) Increases the acidity of the soil
v) Kills fish and other aquatic animals
vi) Pollutes the water
vii) Causes spotting of leaves
viii) Causes corrosion of metal, painted surfaces and even stone buildings and monuments.

Environmental Pollution:

“Destabilization of the balance of the atmospheric composition.

OR

“It is an unstable change in the composition of the environment due to its physical, chemical and biological changes, which is harmful for human life and other animals living on the earth.”

Types Of Pollution:
i) Air pollution
ii) Water pollution
iii) Land pollution
iv) Noise pollution
v) Industrial pollution
vi) Commercial or domestic sector pollution
vii) Chemical pollution
viii) Radioactive pollution (contamination)

Causes of Pollution
The ultimate cause of pollution is human activity itself. Pollution is a human contribution to nature. Science has evolved technologies and technologies have helped the human welfare. In the process, the pollution has been a part of technology and therefore a part of human miseries.

Human activities mainly include:
• Industries for various human needs - directly and indirectly
• Agriculture for food production and industrial needs
• Health care for health of human beings and animals
• Transport for mobility of human beings
• Dwelling for settlement in city or villages
• Energy for various direct human needs and industrial needs.

Pollutants:
Pollutants are those substances which alter the natural composition of the atmosphere or destroy it to harmful level.

Types Of Pollutants:

1. Primary Pollutants
Primary pollutants are those substances which are directly produced by a process. These are:
ix) Sulphur oxides
x) Nitrogen oxides
xi) Carbon monoxide (CO)
xii) Carbon dioxide
xiii) Volatile organic compounds (VOC), such as hydrocarbon fuel vapours and solvents
xiv) Particulate matter (PM), such as smoke and dust.
xv) Metal oxides, especially those of lead.
xvi) Chlorofluorocarbons (CFCs)
xvii) Ammonia (NH3)
xviii) Garbage, sewage and industrial wastes.

2. Secondary Pollutants
Secondary pollutants are those pollutants which are not emitted. Rather, they form in the air when primary pollutants react or interact.
These are:
i) Ground level ozone (O3)
ii) Nitrogen dioxide
iii) Peroxyacetyl nitrate (PAN)

Effects Of Pollution:
1) Air Pollution: Irritation of eyes, nose, mouth and throat, Increased respiratory disease, Cancer, Reduced lung functioning, Premature death. Acid rain, Ozone,
2) Water Pollution: Waterborne diseases such as; Typhoid, Hepatitis, diarrhoea, vomiting, and stomach aches, death of aquatic animals, May disrupt photosynthesis in aquatic plants
3) Soil Pollution: Causes cancers including leukaemia, developmental damage to the brain, kidney damage; depression of the central nervous system, Also causes headaches, nausea, fatigue, eye irritation and skin rash, Contamination of crops, reduce crop yields.

Water Pollution:

Definition:
“The presence of undesirable substances into fresh and natural water which cause harmful diseases in human beings as well as aquatic life is called water pollution.”

Types Of Water Pollution:
Following are the major types of water pollution.
i) Sea-water Pollution
ii) River water Pollution
iii) Land Water Pollution

Causes Of Water Pollution:

1) Pollution Through Domestic Activities:
Domestic activities pollute the water when following kinds of wastes are added.
i) Soap and detergents
ii) Chemicals used in the houses
iii) Waste from slaughter house
iv) Waste from hospitals
v) Waste from bakeries
vi) Human and animal faeces
vii) Waste food

2) Pollution Through Industrial Activities:
Industrial sector is a great source of pollution of water and air. Many industrial units produce waste materials in the shape of solids, liquids and gases. The industrial wastes are.
i) Poisonous gases
ii) Acids, bases and harmful salts
iii) Pesticides and plastics
iv) Radioactive wastes
v) Toxic wastes from fertilizer factories
vi) Wastes from chemical factories

Water Pollution In Pakistan:
In Pakistan people do not take pain to dispose the waste materials in a proper way. Instead of dumping wastes in the drums and places meant for them they freely throw these into the water drains.

Water pollution is very prominent and widespread as a result of urban and industrial activity. Sewage waste from cities and industrial waste are the main factors of water pollution. Many other kinds of wastes which pollute water are from agricultural lands which contain pesticides, waste foods, fertilizers and animal excreta. Wastes from power plants contain radioactive materials, hot water and minerals which also pollute the water. Soaps, detergents, human excreta, animal faeces, wastes from slaughter houses, disease causing micro-organisms from patients and chemicals etc. are drained into water which causes massive water pollution.

Two Important Industries Of Pakistan Causing Water Pollution:
1) One of the biggest sources of water pollution is the tanning and leather industry. The industry uses toxic chromium metal and many other toxic substances/chemicals. These toxins are released in natural waters. Effluent of this industry has polluted ground water and water of nearby rivers. This industry is frequent in Kasur and Sialkot area.

2) Pesticide industry in Kala Shah Kaku near Lahore releases huge quantity of acids, pesticides and other dangerous wastes. These wastes are getting entry into a stream flowing nearby. The water of the stream is dangerously polluted. This water ultimately goes to the rivers.

Effects:
i) Bacteria, viruses, protozoa and worms are carried in polluted water. The diseases caused by them are as under:
a) Bacteria: Typhoid, cholera, Dysentery, enteritis.
b) Viruses: Hepatitis, Polio, Viral enteritis.
c) Protozoa: Amoebic dysentery, diarrhoea.
d) Parasitic worms: Schistostomiasis
ii) It causes death of aquatic animals.
iii) It decreases the fertility of the soil and results in low production.

Methods To Control Water Pollution:
Different methods can be used to control water pollution.
i) The whole sewage waste should be dumped after any treatment.
ii) Sewage treatment plants should be installed in cities.
iii) The sewage waste must not be drained in river to save water from pollution.
iv) Industrial waste should be treated before reaching natural water.
v) Industries should be established away from cities and rivers.
vi) Nuclear dumping in oceans should be banned.
vii) Modern scientific methods should be used in agriculture.

Deforestation:

It is the process of destruction of the forests.

Causes Of Deforestation:
A number of agents are responsible for removal of forests. These are fires. Droughts or animals. The principle agent of deforestation is man himself. Humans are cutting forests to colonize the forest areas or to prepare more agricultural lands or for getting food.

Effects Of Deforestation:
i) Deforestation has many bad effects on human life. With destruction of the forest the process of cleaning of air and production of oxygen is badly affected.
ii) Forests are major agents of evaporation and rainfall. With deforestation rainfall is decreased.
iii) With cutting of forests, pollution is increasing as the hazardous gases are not completely absorbed by plants.
iv) With deforestation carbon dioxide is increasing which is causing global warming.
v) With reduction in area of forest, soil erosion is taking place resulting in floods which destroy crops and human life.
vi) Deforestation has badly damaged wild life and reduced recreation sites.

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Earth:

Features Of Earth:
i) The earth is the fifth largest planet of the solar system, where life exists.
ii) Its equatorial diameter is 7,927 miles.
iii) Its polar diameter is 7900 miles.
iv) The earth has average density of 5 ½ g/cc.
v) the rotation period of the earth is 23 hours, 56 minutes and 4 seconds.
vi) the revolution period of the earth is 365 days.
vii) The total mass of the earth is 6*1021 tons.
viii) The earth is composed of shells or layers, which are, the crust, mantle and core.
ix) It is surrounded by a blanket of gases, which is known as the atmosphere, mainly composed of Nitrogen and Oxygen.
x) The surface of the earth is rich in oxygen, silicon, iron, magnesium, sodium etc.

Structure Of The Earth:
The earth comprises of the following layers:
a) The crust
b) Moho discontinuity
c) The mantle
d) The Core

a) The Crust:
i) It is the outermost layer of the earth.
ii) It extends to about 25 miles (40kms) and comprises of rocks.
iii) The crust is divided into the oceanic and the continental crust.
iv) Out of these the oceanic crust is 808 meter thick and consists of sedimentary mud.
v) The continental crust is divided into upper continental and lower continental crust.

b) Moho discontinuity:
i) The sharp boundary between the crust and mantle is called Moho Discontinuity.

c) The Mantle:
i) The layer of the earth lying below the crust and above the core is known as the mantle.
ii) It is almost 2900 kms (1800 miles) thick and comprises about 80% of the volume of the earth.
iii) The chemical composition of the entire mantle is fairly homogenous.
iv) However, temperature and pressure increases with depth.
v) The behaviour of the earthquake waves as they travel through the mantle further tells us that it consists of several layers and they are:
a) Lithosphere
b) Asthenosphere
c) Mesosphere

d) The Core:
i) The innermost part of the earth is known as the core.
ii) It extends from the base of the mantle to the centre of the earth.
vi) This portion consists of melted iron and nickel that is why it is known as Nife.
vii) The density of this molten mass of the core is 345 pounds per cubic feet.

Types Of Movements Of Earth:
• There are two types of motions of the earth.
• One is around its own axis which is called Rotation. One rotation completes in 23 hours, 56 minutes and 4 seconds.
• The other motion of earth is round the sun, and is called revolution of the earth.
• One revolution completes in 365 days.
• Northern end of the earth’s axis is called the North Pole and the Southern end is called South Pole.
• An imaginary line drawn round the earth midway between the poles is called equator.
• The path which the earth takes round the sun is called earth’s orbit.

Effects Of These Movements:
• Rotation of earth round its axis cause days and nights.
• That portion of earth, which is within the circle of illumination caused by the rays of sun, has its day.
• The other side earth, which is away from sun, remains dark and therefore has its night.

Longer And Shorter Days:
• The circular areas near the North and South Pole of the Earth are called Arctic and Antarctic circles, respectively.
• These are situated at 66 ½0 North and 66 ½0 South of the equator, respectively and form limits of polar region.
• On June, the earth is in position A. north pole is inclined towards the sun and south pole is away from it.
• Obviously any place in Northern Hemisphere will have longer days because it remains in light for more than half the time of earth’s rotation.
• Places on equator remains in light for half the time making days and nights equal in this region.
• The southern hemisphere remains in light for less time than half the rotation of earth so the days are shorter here.
• Positions of days and nights in the northern and southern hemisphere are reversed on 22nd December, when the earth completes its half revolution around the sun, so days are longer in southern hemisphere than those in the north.

Change Of Season:
• The second type of motion of earth is round the sun and is called revolution of the earth.
• This is the cause of change of seasons.
• On June 21, the earth is in position A, when the north pole is inclined towards sun while the south pole is away from it.
• As the sun rays fall vertically and for a longer period in the northern hemisphere, it is summer here but in the southern hemisphere it is winter.
• On December 22, when the earth completes half revolution, the conditions become reversed; it is summer in the southern hemisphere and winter in the northern hemisphere.

Atmosphere:

The layer of the gases which surrounds the earth is known as the atmosphere.
OR
The atmosphere is a thin layer of the gases held to the earth by the gravitational attraction.
OR
Atmosphere is the huge blanket of gas that circles the entire earth.

Composition Of The Atmosphere:
The atmosphere consists of:
i) Nitrogen: 78.03%
ii) Oxygen: 20.99%
iii) Argon: 0.94%
iv) CO2: 0.03%
v) Hydrogen: 0.01%
vi) Neon: 0.0018%
vii) Helium: 0.0005%
viii) Krypton: 0.0001%
ix) Ozone: 0.000001%

Layers Of The Atmosphere:
The atmosphere of the earth is divided into following layers.
i) Troposphere
ii) Stratosphere
iii) Ionosphere
iv) Exosphere
Ionosphere is sub-divided into:
i) Mesosphere
ii) Thermosphere

1) Troposphere:
i) Troposphere is the lowest layer of the atmosphere.
ii) It extends roughly to a height of 8 kms near the poles and 16-18 kms at the equator.
iii) It is troposphere where the people, plants, animals and insects live.
iv) It is the layer where all weather occurs that’s why it is also referred as “The weather Zone”.
v) In the Troposphere temperature gradually falls with increasing altitude.
vi) There is a thin buffer zone between the troposphere and stratosphere is called tropopause.

2) Stratosphere And Ozone Layer:
i) The second layer of the atmosphere is known as the stratosphere.
ii) The stratosphere extends from the tropopause to about 30-31 mile above ground level.
iii) The important ozone layer is found in this region where heat is generated by absorption of UV.
iv) Here the temperature either remains constant or increases with altitude.

Stratopause:
It is the upper boundary of the stratosphere which occurs beyond 52 kms. Here the temperature remains constant with increase in height.

3) Ionosphere:
i) The third major layer of the atmosphere is the ionosphere.
ii) It lies above the stratosphere.
iii) It lies between about 30 and 90 miles above the surface of the earth.
iv) It is divided into mesosphere and thermosphere.
v) The ionosphere is bombarded by cosmic radiation and solar x-rays, which causes the gases in the ionosphere to ionize.
vi) Brilliant displays of colored lights in the sky called Aurora Borealis in the northern hemisphere and the Aurora Auralis in the southern hemisphere occur when streams of electrically charged particles from the sun (solar wind) ionize the atmosphere gases.

4) Exosphere:
i) The uppermost layer of the atmosphere extending beyond Ionosphere is called exosphere.
ii) Beyond 300 miles is the very rare field exosphere which consists only of scattered atmosphere of O, H and He.

Latitude:

Definition:
It is the distance on the surface of the earth measured in degrees north and south of the equator.
The equator is at zero degree where the poles are at 90 degree. The latitude of the north pole is 900 North and that of south pole is 900 South.

Characteristics OF Lines Of Latitudes:
i) All lines of latitudes are parallel to the equator as well as parallel to one another.
ii) Parallels in the north of the equator are north latitudes while those in the south of equator are known as south latitudes.
iii) They are drawn on the globe as circles running in east to west direction.
iv) The length of the equator is the maxim um and it goes on reducing till the pole is only a point.

Longitude

Definition:
The distance on the earth’s surface measures in degrees east and west of a line joining the geographical north and south poles and passing through Greenwich in England. Greenwich is at zero degrees longitude.

The sun rays have highest altitude simultaneously on all the places at a particular line of longitude as a result of which these are also called as Meridians (Meridian is a Latin word which means Mid-way). Among the latitude, equator is the longest and is taken as reference line. But all the lines of longitude are of the same length and selecting a longitude as lines of reference is a serious problem.

Earthquake:

Earthquakes are those movements of the earth crust which make the ground vibrated and shake backwards and forwards or in simple words an earthquake is trembling in the earth.

The shocks waves are generated at a point within the crust called the focus, and the point on the earth’s surface vertically above the focus is called the epicentre of the earthquake. The shock waves travel in all directions from the focus. On the earth’s surface, the shaking is the strongest near the epicentre. These waves are detected by seismograph.

Occurrence Of Earthquake:
i) Earthquakes occur when rocks subjected to great stress suddenly break, releasing the accumulated energy, which shakes the ground. Vibrations spread out from the epicentre like ripples in water.
ii) It may also be caused by movements of the plates, resulting from convection currents in the hot mantle of the earth.
iii) Earthquakes are also associated with volcanic activity-eruption of magma. Collapse of mines can also produce small earthquakes.

Volcanoes:

An opening in the earth's crust through which molten lava, ash, and gases are ejected.

Occurrence Of Volcanoes:
i) Rocks below the Earth have a very high temperature.
ii) The great pressure upon these keeps them in a semi-solid state.
iii) If the pressure weakens, then some of rocks become liquid.
iv) This liquid is called magma.
v) The magma forces its way into cracks of the crust and may either reach the surface of the earth where it forms lava and flow out.

Types Of Volcanoes On The Basis Of Activity:
There are three types of volcanoes on the basis of volcanic activity, which are as under.

i) Active Volcanoes:
Volcanoes are said to be active when they frequently erupt or at least when they have erupted within recent time.

ii) Dormant Volcanoes:
The volcanoes that have been known to erupt and show signs of possible eruption in the future are describes as dormant volcanoes.

iii) Extinct Volcanoes:
The volcanoes that have not erupted at all in historic times but retain the features of volcanoes are termed as extinct volcanoes.

Causes of The volcanoes Eruptions:
i) Seafloor spreading
ii) Convergence of lithospheric plates
iii) Percolation of cold water
iv) Orogenic Movements
v) High temperature in the interior of the Earth