8th Std Social Science Notes.
by Veeresh. P
Geography
THE EARTH-OUTERLIVING PLANET
l. Fill in the blanks with suitable answer:
1. The total geographical area of the Earth is______Sq. Kms
2. The shape of the Earth is ______
3. The equatorial and polar diameter of the Earth is _______ and _________ Kms.
4. The 23½ North latitude is called as ____________
5. The Indian Standard Time is based on _________ longitude.
Ans: (1) 510 million (2) Geoid (3) 12756, 12714
(4) Tropic of Cancer (5) 82½ East
II. Answer the following questions briefly:
1. Why is the Earth called 'Living Planet'?
Ans: The Earth is the home for all forms of life like plants, animals and human beings because of its suitable distance from the Sun, range of temperature, life supporting gases, atmosphere, water cycle, etc. It is the only planet that supports life that is why it is called 'Living Planet'.
2. Why are the Northern and Southern hemispheres called Land and Water Hemispheres?
Ans: The Northern Hemisphere has 60% of land and 40% of water. Therefore it is called the 'Land Hemisphere. The Southern Hemisphere has 81% of water and 19% of land in the Southern Hemisphere. So it is called the 'Water Hemisphere'.
3. What are latitudes and longitudes?
Ans: Latitude- is a horizontal imaginary line which joins all the places which have the same angular distance north or south of the equator. It is measured in degrees.
Longitude- The imaginary vertical lines that intersect equator at right angle joining the north and south are called longitudes.
4. Mention the difference between local time and standard time.
Ans: Local Time: The time according to the longitude of a place or according to the position of the Sun at the place is known as the Local time. This is based on the local meridian passing over that place. When the Sun is shining vertically over the longitude it is 12 noon at that place. All places situated on the same meridian have the same local time. Every longitude has its own local time.
Standard Time: To avoid much confusion that arises from following the local time which differs from place to place, many countries follow uniform time throughout the country. Such uniform time is based on the central meridian of the country or the meridian on which the most important city is located. This uniform time which is followed throughout a country is called Standard Time of that country.
5. What is the International Date Line?
Ans: The circum navigation of the world brought a new problem in keeping the correct date and day in the week for the travellers. Therefore a line passing through 180 degree meridian diametrically opposite to the GMT(Greenwich Meridian Time) was adopted as the point where circumnavigation should make adjustments. This line is supposed to pass Pacific Ocean along the 1800 meridian but makes short detours in order to avoid land masses. This is known as the International Date Line because the date and day is changed whenever people cross this line by ships or airplanes.
III. Define the following:
1. Unique planet: The Earth is called a Unique Planet because of its features. It is the only planet that supports life. The Earth is the home for all forms of life like plants, animals and human beings because of its suitable distance from the Sun, range of temperature, life supporting gases, atmosphere, water cycle, etc.
2. Size of the Earth planet: The Earth is the fifth largest planet in the Sun's family. The diameter of the earth is approximately four times greater than the Moon and it is around 107 times less than that of the Sun. The total geographical area is 510 million sq. kms.
3. Geoid: The shape of the earth is often described as Geoid, which literally means 'Earth shaped', or 'Oblate spheroid'. The earth is flattened at the poles and bulges at the equator. The equatorial diameter of the Earth is 12756 kms and the Polar diameter is 12714 kms, Equatorial circumference 40,008 kms. The difference of 42 kms in diameter is the proof for regarding the Geoid shape of the Earth.
4. Continents: The land bodies of the Earth are known as
Continents. There are seven continents, namely Asia, Africa, North America, and South America. Antarctica, Europe and Australia. The continents are land masses of large size. Asia is the largest continent and Australia is the smallest continent in the world.
5. Prime Meridian: Lines of longitude are called Meridians
(‘meri'-mid and 'dian'-day) because all places along the same meridian of longitude experience noon or mid-day at the same time. The meridian passing through Greenwich (England) has been chosen as Prime Meridian. It is marked as 00 longitude.
6. Indian Standard Time: In India, 82½ East longitude is
considered as the Standard Meridian of the country. It passes through Allahabad of Uttar Pradesh. The time based on this Meridian is called the Indian Standard Time (IST). It is five hours and 30 minutes ahead of GMT.
LITHOSPHERE
I Fill in the blanks with suitable words :
1. The continental crust is also called ___________
2. Vast basin shaped volcanic mouth is ___________
3. The most destructive earthquake waves are ________
4. Stalactites and stalagmites are most common in _______
5. The Beaches are formed by ________ work.
Ans: (1) SlAL, (2) Caldera, (3) surface waves,
(4) lime stone region, (5) sea waves.
II. Answer the following questions:
1. Mention the three major layers of the interior of the
Earth.
Ans: The three major layers of the interior of the Earth are
(1) The Crust (2) The Mantle and (3) The Core.
2. Name the types of volcanoes on the basis of frequency of
eruption.
Ans: On the basis of frequency of eruption volcanoes are classified into three types. They are-(1) Active Volcanoes, (2) Dormant Volcanoes and (3) Extensive Volcanoes.
3. Mention the important earthquake zones of the world.
Ans. The important earthquake zones of the world are-
(1) The Circum-Pacific Belt-Regions around the Pacific Ocean (New Zealand, Philippines, Japan, USA, Peru, etc.)
(2) The Mediterranean Belt- Regions around the Mediterranean Sea.
(3) The Himalayan Belt- The Siwalik regions of India.
4. What is weathering? Name the three main types of weathering.
Ans: Weathering is the wearing away or breaking down or gradual disintegration of rocks by agents like temperature, rainfall, wind etc., present in the atmosphere.
The three types of weathering are as follows-
(1) Mechanical weathering,
(2) Chemical weathering and
(3) Biological weathering.
5. Name the landforms associated with the work of river.
Ans: The important landforms in the middle course of the river are Alluvial fans and Meanders. The important land forms in the Lower Course of the river are flood Plains, Natural Levees, Ox-bow lakes, Deltas.
III. Match the following:
A B
1. Sima a) Earthquake
2. Sandstone b) Yellow soil
3. Epicentre c) Oceanic crust
4. Geyser d) sedimentary rock
5. Loess e) underground water
Ans: 1-c, 2-d, 3-a, 4-e, 5-b.
IV. Define the following:
1. Aqueous rocks: Sedimentary Rocks are also called aqueous rocks because they are formed in the water bodies like lakes, seas, and ocean beds.
2. 'Pacific ring of fire': Pacific ring of fire is a region of Volcanoes. The regions are The Coastal margins of the Pacific Ocean consisting of Philippines, Japan, USA, Central America, South America, etc.
3. Mechanical weathering: When the rock is broken and disintegrated without any chemical alteration, the process is called Physical weathering or Mechanical weathering. The important processes of mechanical weathering are Granular disintegration, Block disintegration and Exfoliation. The agents of mechanical weathering are temperature, wind, frost, etc.
4. Carbonaceous rocks: Coal is called carbonaceous rock. Organic sediments are derived by the accumulation of remains of organisms, such as shells of marine organisms, remains of plants and animals, Example Carbonaceous rocks are coal and limestone.
5. Tsunami: Tsunami is a large sea wave occasionally experienced along the coasts of Japan and in other regions caused by underwater earthquake. In Japanese language 'Tsunami' means 'harbour waves'.
6. Continental glacier: Continental glacier are extensive ice sheets found in polar regions E.g. Greenland and America.
7. Hot spring: Whenever warm or hot water comes out naturally it is called hot spring or thermal spring. They are usually found near the volcanic regions.
ATMOSPHERE
I. Fill in the blanks with suitable words:
1. The two major gases of the atmosphere are ______ and _________
2. The lowest layer of the atmosphere is ________
3. The average air pressure of the atmosphere at the sea level is ___________
4. Westerlies is also known as ___________
5. The scientific study of weather is ___________
Ans: (I) nitrogen, oxygen (2) Troposphere (3) 1013.25mb
(4) Trade winds (5) Meteorology.
II. Answer the following questions:
1. What is atmosphere?
Ans: Atmosphere is a thin layer of gases, dust particles and water vapour surrounding the earth. This layer of gases forms protective boundary between the outer space and the earth's surface.
2. Name the important layers of the atmosphere.
Ans: (a) Troposphere, (b) Stratosphere, (c) Mesosphere,
(d) Thermosphere (e) Exosphere.
3. What is the significance of ozone layer?
Ans: Ozone layer absorbs ‘ultraviolet rays’ of the sun and protects all forms of life on the earth.
4. What is Doldrums? Where is it found?
Ans: The Equatorial low pressure belt is called Doldrums. This region gets direct rays of the Sun almost throughout the year. This is a calm region with very little wind so it is called Doldrums. Doldrums means belt of calmness. This region lies between 0° to 5° North and South of the equator.
5. Name the different types of planetary winds.
Ans: There are three types of planetary winds. They are-
(a) Trade winds, (b) Anti-trade winds and (c) Polar winds.
6. What are local winds? Give any two examples.
Ans: Periodic winds are the result of variation in local temperature, pressure, humidity which in turn are attributed to the formation of air currents, crossing mountain ranges, valleys and other relief barriers. The important periodic and local winds are Land breeze, Sea breeze, Mountain breeze, valley breeze, etc.
7. Mention the different types of clouds.
Ans: The different types of clouds are- the Stratus, the Cumulus, the Cirrus and the Nimbus clouds.
8. Distinguish between weather and climate.
Ans: Weather: The atmospheric condition of a smaller area at a particular time is called weather. For example cloudy, sunny, fine weather, etc.
Climate: Climate is the average condition of the atmosphere over a long period of time of a larger area. Example- Equatorial climate, Tropical climate, etc.
III. Define the following:
1. Ionosphere: Thermosphere is called Ionosphere as the gaseous atoms are ionized due to very high temperature. The ions found in this layer help in reflecting radio waves.
2. Normal lapse rate: It is the decreasing rate of temperature with the increase of altitude. The rate of decrease is 1° C for every 165 meters or 6.4° for every 1000 meters of height.
3. Torrid Zone: Torrid Zone is the zone of high temperature. This region is found between O° or equator and Tropic of Cancer (23½° N) in the north and the Equator and Tropic of Capricorn (23½° S) in the south. This region receives direct rays of the sun.
4. Horse latitudes: Sub-tropical high pressure belts that lie between 30° and 35° north and south of the equator are high pressure belts. The North sub-tropical high pressure belt that lies between 30° and 35° north are also called 'Horse latitude'.
5. Orographic rainfall: Orographic rainfall is also called 'Mountain rainfall' or 'Relief rainfall'. When moisture laden air is obstructed by a mountain barrier, the air is forced to rise up. As the air rises upwards, it cools and gets saturated. Further cooling of this air causes condensation resulting in orographic rainfall.
6. Climatology: The scientific study of climate is called
Climatology.
HYDROSPHERE
l. Fill in the blanks with suitable words:
1. The average depth of the continental shelf is _______
2. One fathom is equal to ________ft.
3. The deepest place in the Pacific Ocean is __________
4. The average salinity of the ocean water is __________
5. ___________ tides occur during full moon.
Ans: (1) 100 fathoms (2) six (3) the Challenger deep of Mariana Trench (4) 35 parts of 1000 (35/) PPT (5) Spring
II. Answer the following questions:
1. What is hydrosphere?
Ans: 71% of the total area of the Earth is surrounded by water. This is called hydrosphere.
2. Mention the four major parts of the ocean floor.
Ans: The four major parts of the ocean floor are –
(1) Continental Shelf
(2) Continental slope
(3) The Deep sea plain and
(4) The Ocean deep.
3. State the difference between ocean currents and tides.
Ans: Ocean currents are the regular movement of ocean water from one region to another.
Tides are the periodic rise and fall in the sea or ocean level.
4. Distinguish between spring tide and neap tide.
Ans: Spring tide: Spring tide takes place when the earth, the moon and the sun are in the same straight line. E.g. New Moon and Full Moon. When the spring tides take place, high tides are the highest and the low tides are the lowest.
Neap Tide: Neap tides occur on the first quarter and last quarter days in the phase of the Moon. During neap tides the sun and the earth are in the same straight line and moon in the right angle to the earth. In this type of tides the high tides are not very high and low tides are not very low.
5. How can we conserve the oceans?
Ans: We can conserve oceans through following methods:,
(1) Oil transportation should be done through pipelines.
(2) Nuclear waste should not be dumped into sea or ocean.
(3) Petro-chemical industries in the coastal regions must avoid dumping effluents into the sea or ocean.
(4) Dumping of any waste near the ports and harbours must be controlled.
(5) Ore deposition and mineral exploitation along the coast must be controlled.
(6) Exploitation and destruction of beaches must be controlled.
III Match the following:
A B
1. Fathom (a) deep sea plain
2. Oyashio (b) eastern coast of USA
3. Gulf stream (c) cold current
4. Sea mounts (d) Indian ocean current
5. Agulhas current (e) depth of ocean
Ans: 1-e, 2-c, 3-b, 4-a, 5-d.
IV. Define the following:
1. Continental shelf:- Continental shelf is the shallow area along the sea coast. This part is bordered by the sea coast on one side and continental slope on the other side. The average depth of the continental shelf is 100 fathoms.
2. Salinity: Salinity is the percentage of salts dissolved in the sea or ocean water. The average salinity of the ocean water is 35 parts per thousand.
3. Warm and cold currents: Warm currents originate and flow from the equatorial regions to sub-polar regions.
Cold currents originate in the Polar Regions and flow towards the equatorial region.
4. High tide and Low tide: High tide, also known as Flood tide and Low tide also known as Ebb tide. On the water bodies of the earth there are alternate high tides and low tides. Between one high tide and a low tide the time is 6 hrs, 13 minutes. Between one high tide and another, the time gap is 12 hrs, 26 minutes. In 24 hrs, 52 minutes there are 2 high tides and 2 low tides.
5. Benguela current: Benguela current is the cold currents of South Atlantic Ocean.
6. Tides: Tides are the periodic rise and fall in the sea or ocean level. They occur due to gravitational attraction by the moon, gravitational force by the sun, rotation of the earth and centrifugal force of the earth.
BIOSPHERE
I Answer the following questions:
1. What is Biosphere?
Ans: Biosphere is a part of the earth where life exists. It is the fourth component of the earth and it is the totality of all living things on earth.
2. Define ecology?
Ans: Ecology is the study of the interaction of living organisms with their physical, chemical and biological environment.
3. Name the different types of environmental pollution.
Ans: The different types of environmental pollution are-
(1) Air pollution, (2) Water pollution,
(3) Soil pollution and (4) Noise pollution.
4. What are the measures to control water pollution?
Ans: Some measures to control water pollution are-
(a) Industrial effluents must be treated,
(b) Drinking water sources must be kept clean,
(c) Sewage treatment plants,
(d) Disposal of waste on the water bodies must be controlled, etc.
5. What is Bio-diversity?
Ans: The variety of flora (plants) and fauna (animals) in a region is known as biodiversity.
II. Define the following:
1. Biosphere: Biosphere is a part of the earth where life exists. It is the fourth component of the earth and it is the totality of all living things on earth.
2. Ecological imbalance: In a natural environment, there is a perfect balance between the various organisms living together in the biosphere. This is known as ecological balance. When this balance is disturbed due to various reasons, it leads to ecological imbalance.
3. Global warming: The temperature of the earth is increasing slowly over the years. For the last few years global temperature has increased. This phenomenon is termed as Global warming.
4. Greenhouse effect: The energy that the earth receives from the sun has to be balanced by the radiation emitted from the earth's surface. The use of fossil fuel is increasing green house gases in the atmosphere. Carbon dioxide and other greenhouse gases trap the heat radiated from the earth. Thus increasing of greenhouse gases is causing an increase of temperature. This is called 'Greenhouse effect’
5. Ozone depletion: In recent years the use of air conditions, refrigerators, sprays and deodorants are destroying the ozone due to the synthetic chemicals released into the atmosphere, primarily 'chlorofluorocarbons'(CFC). The ozone depletion has caused the ozone hole.
6. Acid rain: Acid rain contains high amounts of acids particularly sulphuric acid and carbon monoxide. It is caused when the rain drops pass through the polluted atmosphere. The rainfall with poisonous acids kills marine organisms. Acid rain is damaging forests, agricultural crops, old buildings, monuments, etc.