Geography Class 07 NCERT

Posted by
    1. Environment is our basic life support system, provides air we breathe, water we drink, food we eat and land where we live.
      1. It is combination of natural and human made phenomena.
      2. Natural environment is both biotic and abiotic conditions, human environment reveals activities, creations and interactions among human beings.
      3. Natural environment - Lithosphere is solid crust of the earth, made up of rocks and minerals and covered by thin layer of soil. Irregular surface with landforms, found over continents and ocean floors.
      4. Hydrosphere - domain of water, comprises various source of water and different types of water bodies, essential for ALL living organisms.
      5. Atmosphere - thin layer of air that surrounds the earth. Gravitational force of earth holds the atmosphere around it. Protects us from harmful rays and scorching heat of sun. Changes in atmosphere produces changes in weather and climate.
      6. Biosphere - narrow zone of earth where land, water and air interact with each other to support life.
      7. Ecosystem - system formed by interaction of all living organisms with each other and with physical and chemical factors of environment in which they live, all linked by transfer of energy and material.
      8. Human Environment - human beings interact and modify it according to our needs.
    2. Interior of our earth
      1. Crust forms 1% volume of earth, 84% is mantle and 15% core.
      2. Radius of earth 6371 km
      1. Crust
        1. thinnest of all layers, 35 km on continental masses and 5 km on ocean floors.
        2. Main mineral constituents of continental mass are silica and alumina (called sial / felsic, 2.7 times denser than water).
        3. For oceanic crust - silica and magnesium (sima / mafic, 3.4 times denser than water).
        4. Oceanic is thinner, denser and younger than continental crust.
        5. Continental crust is predominantly granitic rock (see granite), while composition of the oceanic crust corresponds mainly to that of basalt.
        6. Crust consists of mainly igneous rocks, and sedimentary and metamorphic rocks.
      2. Mantle - 100-2900 km thick. Composed of silicate material
      3. Core - 2900-5100-6370 km thick.
        1. Made up nickel and iron, very high temperature and pressure.
        2. Inner core is rotating and cause of earth's magnetic field.
      4. 3 major types Rocks
      5. Rocks and minerals - any natural mass of mineral matter that makes up earth's crust is called a rock.
      6. Igneous - when molten magma cools, it becomes solid and thus formed rocks are called igneous rocks (also called primary rocks).
        1. 2 types
          1. intrusive rocks (when molten lava cools down slowly deep inside earth's surface, large grain, eg granite)
          2. extrusive rocks (when molten lava cools down rapidly after coming on earth's surface, fine grained structures, eg basalt).
      7. Sedimentary
        1. Rocks broken down into small fragments, transported and compressed and hardened to form layers of rocks are called sedimentary rocks. Eg sandstone (made from grains of sand). May contain fossils of plants/animals.
      8. Metamorphic - igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure.
        1. Eg clay changes into slate and limestone into marble. Rock cycle
  • Our changing earth
    Lithosphere is broken into a number of plates known as lithospheric plates which move around very slowly - few "mm" each year - cos of movement of molten magma.
    1. Earth movements are divided on the basis of forces which cause them -
      1. Endogenic forces
        1. Sudden forces eg earthquake, volcano, landslide
        2. Diastr ophic forces eg building mountains
      2. Exogenic forces
        1. erosional and depositional such as river, wind, sea waves, glaciers
    2. Earthquake - when lithospheric plates move, surface of earth vibrates: the vibrations are called earthquake.
      1. Focus - place in crust where mo vement starts.
      2. Epicenter - place on the surface above the focus.
      3. Earthquake measured with seismograph, magnitude of earthquake is measured on Richter scale (measured in logarithmic scale, 3.0 to 4.0 is 10x).
      4. Types of earthquake waves
        1. Primary waves or longitudinal waves
          1. push and pull waves, resemble sound waves. Travel outward from point of disturbance in all directions in straight lines.
          2. Fastest of all earthquake waves. P and S waves cause the rocking motion of the earth.
        2. Secondary/shear waves (or) transverse waves
        3. L waves or surface waves (love and rayleigh)
    3. Major land forms
      1. landscape is being continuously worn away by 2 processes
      2. weathering and erosion.
        1. Weathering is the breaking up of rocks on earth's surface.
        2. Erosio n is wearing away of the landscape by different agents. These 2 processes created different landforms on surface of earth.
      3. Rivers - twists and turns forming large bends are called meanders.
        1. When meander loop cut off from the river and forms a cut off lake, its called an ox bow lake.
        2. Floodplains - formed by overflowing rivers depositing layers of fine soil and sediments.
          1. The raised banks are called levees.
          2. As i approaches seas and begins to break up into distributaries which has own mouth, the collection of sediments from all the mouths forms a delta.
        3. Sea waves - erosion and deposition of sea waves gives rise to coastal landforms.
          1. Sea caves, sea arch, stack (only wall after roof of arch is gone).
          2. Sea waves deposit sediments along the shores forming beaches.
        4. Ice - glaciers are river of ice which erode the landscape by bulldozing soil and stones to expose the solid rock below.
          1. Glacial moraines - material deposits carried by the glacier.
      4. Wind - mushroom rocks (narrow base, wider top).
        1. Wind causing low hill structur es are called sand dunes.
        2. Loess - deposits of grains of sand (fine and light) carried over by wind over long distances

    (eg China).

    1. Air
      1. carbon dioxide in the atmosphere creates a green-house effect by trapping the heat radiated from the earth - called greenhouse gas and without it earth would have been too cold to live in.
        1. But when heat retained increases (due to human activity),
        2. the temperature of the earth goes up = global warming. Snow melts -> sea level rises -> floods in coastal areas.
        3. Plants cannot take nitrogen (needed for survival) directly from air.
          1. Bacteria that live in the soil and roots of some plants take nitrogen from air and change its form so that plants can use.
          2. Green plants produce oxygen during photosynthesis, use carbon dioxide to make food and release oxygen. Plants CO2 in = humans CO2 out.
      2. Atmosphere - 5 layers
        1. Troposphere - most imp layers, height 13 km. the air we breathe exists here.
          1. Most weather phenomena occur i n this layer
        2. Stratosphere - 13-50 km. Almost free from clouds and associated weather phenomenon, ideal for airplanes.
          1. Contains layer of ozone gas.
        3. Mesosphere - 50-80 km.
          1. Meteorites burn up in this layer upon entering from space.
        4. Thermosphere - 80-100 km.
          1. Temperature rises very rapidly with increasing height.
        5. Ionosphere (80-1000 km) part of this layer.
          1. Ionosphere is ionized by solar and cosmic radiation: atoms have been stripped of one or more electrons and are positively charged.
          2. This layer helps in radio transmission (transmitted from earth and reflected back to earth)
        6. Exosphere - upper most layer of atmosphere, very thin air.
          1. Light gases like helium and hydrogen float into space from here.
          2. Earth receives 1/200b parts of sun's energy.
      3. Weather - day to day condition of the atmosphere.
        1. Climate is average weather condition of a place for a longer period of time.
        2. Distribution of temperature is influenced by insolation; which is incoming solar energy intercepted by earth.
          1. Amount of insolation decreases from the equator towards the poles.
          2. Why are cities hotter than villages - the concrete and metal and asphalt gets heated during the day and released during the night.
        3. Air pressure and us - air presses us from all directions and our body exerts a counter pressure.
          1. Air pressure is highest at sea level and decreases with height.
          2. Horizontally, air pressure influenced by temperature of air.
          3. Air always move from high pressure to low.
            1. Low pressure area - cloudy skies and wet weather (Mumbai).
            2. High pressure area - clear and sunny skies (Ladakh).
            3. No air on moon means no pressure.
            4. The counter pressure exerted by human body will make blood vessels burst.
      4. Wind

    � Wind - movement of air from high pressure area to low pressure area is called wind.

    3 types of wind

    1. Permanent winds
    2. Seasonal winds
    3. Local winds
    1. Moisture - moisture in the air at any time is called humidity.
      1. As air gets warmer, its capacity to hold water vapor increases so it becomes even more humid.
      2. When water vapor rises it starts cooling and condenses causing formation of clouds.
      3. When it becomes too heavy, it comes down as precipitation.
      4. Jet trail is condensed moisture from their engines.
    2. Types of rainfall
      1. Cyclonic rainfall
      2. Orographic/relief rainfall
      3. Convectional rainfall
    1. Water
      1. Water cycle - process by which water continually changes its form and circulates between oceans, atmosphere and land. Same water that existed centuries ago exists today.
        1. Salinity is amount of salt in grams present in 1000g of water. Avg salinity is 35 parts per 1000.
        2. Dead Sea in Israel has 340g/kg of water.
        3. Rivers have the least amount of fresh water.
        4. 75% of fresh water is in ice caps.
        5. 22 March World Water Day.
      2. Ocean circulation - movements that occur in oceans can be categorized as
        1. Waves - formed when winds scrape across the ocean surface:
          1. stronger the wind blows, the bigger the wave becomes.
          2. First indication of tsunami is rapid withdrawal of water from coastal region (as water displacement happens to fill in displacement between continental plates),
          3. follow ed by destructive wave
        2. Tides - rhythmic rise and fall of ocean water twice in a day.
          1. High tide when water covers much of the shore by rising to highest level, low tide when water falls to lowest level and recedes from the shore.
          2. Why - strong gravitational pull exerted by the sun and moon on the earth's surface causes the tides.
            1. High tide - caused by gravitational force of moon. During full moon and new moon - sun, moon, earth in same line and tides are highest (spring tides).
              2. First and last quarter of moon, diagonal pull from both sun and moon results in lowest tides (neap tides).
            2. High tide - useful in navigation, fishing.
        3. Currents
          1. Streams of water flowing constantly on the ocean surface in definite directions, can be cold or warm.
          2. Generally warm ocean currents originate near equator and move towards the pole. Ocean current influences the temperature conditions of the area.
          3. Areas where warm + cold current meet = best fishing grounds in the world + foggy weather difficult in navigation.
    2. Natural vegetation + wild life
      1. 3 types of natural vegetation - forests, grasslands & shrubs.
        1. Forests
          1. Tropical evergreen forests - thick forests in region near equator and close to tropics.
            1. No particular dry season hence trees don't shed their leaves.
            2. Hardwood trees like rosewood, ebony, mahogany.
          2. Tropical deciduous forests - monsoon forests. In N&C India, North Australia, Central America.
            1. Seasonal rains - trees shed leaves in dry season to conserve water.
            2. Hardw ood trees like sal, teak, neem, sheesham.
            3. Animals - tigers, lions, elephants, langoors, monkeys.
          3. Temperate evergreen forests - mid latitudinal coastal region eg SE USA, South China, SE Brazil.
            1. Hardwood and softwood trees like oak, pine, eucalyptus.
          4. Temperate deciduous forests - Higher latitudes such as NE USA, China, New Zealand, Chile, coastal West Europe.
            1. Common trees - oak, ash, beech. Deer, foxes, wolves are found.
          5. Mediterranean vegetation - orchards of the world cos of fruit cultivation.
            1. West and SW margins of continents. Europe, Africa, Asia around Mediterranean sea, hence the name. But also found in California, SW Australia, SW Africa/S. America.
            2. Hot dry summers and mild rainy winters - good for citrus fruits - wine! Not much wildlife.
          6. Coniferous forests/boreal - around arctic circle coniferous forests are found also called taiga (meaning untouched).
            1. Tall softwood evergreen trees such as chir, pine, cedar - useful in making pulp.
        2. Grasslands
          1. Tropical grasslands - either side of equator and extend till tropics.
            1. Grows in moderate to low rainfall areas, avg 3-4 meters height (tall!).
            2. Savanna grasslands in Africa, elephants, zebras, giraffes, deer, leopards.
            3. Campos (Brazil)
            4. Llanos (Venezuela).
          2. Temperate grasslands
            1. Pampas (S America/Ag),
            2. Prairie (N America),
            3. Veld (S Africa),
            4. Steppe (C Asia),
            5. Down (Australia)
        3. Shrubs - found in dry desert like regions,
          1. western margins of continents.
          2. Called tundra in polar region (mosses, lichens - grows in short summers).
    3. Human environment
      1. Transhumance - seasonal movement of people
      2. Transport - roadways, railways (Trans-Siberian Railway from St Petersburg to Vladivostok)
      3. Waterways (2 types - inland sea routes, Shanghai port the busiest)
      4. Airways� (Atlanta is busiest, Delhi in India growing fastest).
    4. Tropical & subtropical life
      1. Amazon basin
      2. Equator passes thru 13 countries (Indonesia and Maldives in Asia; Ecuador, Columbia & Brazil in Africa).
      3. Agriculture practices are slash and burn.
      4. Maloca - houses with steeply slanting roof.
    5. Ganga-Brahmaputra river system
      1. Brahmaputra
        1. Origin is Angsi Glacier near Mount Ka ilash. Enters India after a u-turn at Namcha Barwa (u-turn forms longest and deepest Grand Canyon in the world - Yarlung Tsangpo Grand Canyon).
        2. Imp tributaries - Teesta and Manas
          1. largest river of Bhutan, its river valley is home to Royal Manas National Park in Bhutan
            2. the contiguous Manas Wildlife Sanctuary of India which is a Project Tiger Reserve, an Elephant Reserve and a Biosphere Reserve as well as a UNESCO World Heritage Site
        3. Blind dolphin susu = National Aquatic Animal = Ganges river dolphin
    6. Temperate life
      1. Grasslands 25% of total land surface.
      2. World's grasslands divided into 2 regions. Temperate and Tropical.
        1. Prairies - bound by Rocky Mountains in west and Great Lakes on east, practically tree less.
          1. Home to native Americans. (Chinook is hot wind that blows in winter raising temperatures, because of absence of north-south barrier).
          2. Prairies are "granaries of the world" due to surplus wheat production.
          3. Dairy farming + extensive agriculture = food processing industries.
          4. Large mineral deposits as well.
        2. Veld - temperate grasslands of South Africa.
          1. Velds are rolling plateaus, bound by Drakensberg on east and Kalahari desert on west.
          2. Rivers - Orange and Limpopo.
          3. Soil not very fertile - cos of discontinuous grass exposing barren surface. Rich reserve of minerals.
        3. Deserts - arid region characterized by extremely high or low temperatures and scarce vegetation.
          1. Sahara - world's largest desert covering 8.5 million sq. km, 11 countries. Nomadic tribes - Bedouins and Tuaregs.
          2. Depressions are formed when wind blows away the sands. In the depressions where underground water reaches the surface, an oasis is formed.
          3. These areas are fertile and can support human population. Tafilalet oasis is in Morocco, area of 13k sq km. La dakh/Khapa-chan - meaning mountain pass country.
          4. Cold desert in Greater Himalayas, enclosed by Karakoram range in north and Zanskar mountains in south.
            1. Endangered species - chiru or tibetan antelope.
            2. Buddhist monasteries with gompas.

Comments

Post a Comment