Geography notesexpo

  • Study of universe is called cosmology.
  • Galaxy = stars + planets + gases + dust.
  • Our nearest galaxy is Andromeda.
  • Milky Way contains 300 billion stars.
  • In AD 140, Ptolemy gave theory that earth is at the centre of the universe and sun and the other heavenly bodies revolve around.
  • In 1543, Copernicus stated that sun is at the centre of the universe and not earth.
  • Kepler supported Copernicus but said that sun is centre of the solar system not universe.
  • In 1924, Edwine Hubble first demonstrated existence of galaxies beyond Milky Way.
  • Structurally galaxies are found in three forms.
    • Spiral: – Have a central nucleus with great spiral arm. E.g. Milky Way and Andromeda.
    • Elliptical: – Without spiral arm.
    • Irregular: – With no shape.
  • Evolution of universe
    • Big bang theory:- By Georges Le Maitre.( explosion occurred 13.8 billion years ago)
    • Steady state theory: – By Bondi, Gold and Fred Hoyle. ( it has no beginning and no end)
    • The pulsating theory: – At present universe is expanding.
  • Components of solar system
    • Sun, eight planets and their respective satellites.
    • Interstellar debris such as asteroids, meteroids, comets.
    • Electrically charged gases called plasma.
    • Inter planetary dust particles.
    • And small solar system bodies (SSSB).( other than planets, dwarf planets and satellites)
  • Various theories were given to explain origin of solar system
         HYPOTHESIS PROPOUNDER
1.      Gaseous Kant
2.      Nebular Laplace
3.      Planetesimal Chamberline and Moulton
4.      Tidal Sir James jeans and Harold jeffreys
5.      Binary star H n Russell
6.      Supernova F hoyte
7.      Inter stellar dust Otto Schmidt
8.      Electromagnetic H Alfven
9.      Protoplanet G kuiper
10.  Nebular cloud Dr Von weizsacker
  • Sun
    • Nuclear fusion reaction, converts hydrogen into helium in the core of the sun.
    • Superimposed on sun’s white light are hundred of dark lines called fraunhofer lines. Each line indicates some elements present in the solar system.
    • Solar winds: – The sun is continuously emitting streams of proton in all directions either as spiral streams called solar wind or bouts of incandescent material called solar flares. Solar flares being hot ionized gases pose danger to satellite communication.
    • Aurora: – The constituent particles of the solar wind are trapped by the earth’s magnetic field and enters the earth’s upper atmosphere as aurora. It is described as aurora borealis in northern hemisphere and aurora australis in southern hemisphere.
    • The surface of sun is continuously changing. Bright spots are called plages and dark spots are called sunspots. The sun spots are cold and dark regions on the sun’s surface with a periodicity of 11 years, these spots greatly influence the global climate.
  • Planets
    • Mercury
      • Rotation period – 58.65 days.
      • Revolution period – 88 days. (fastest)
      • No satellite.
      • Highest diurnal range of temperature.
    • Venus
      • Earth’s twin, morning/evening star.
      • Brightest after sun and moon because of 70% of albedo.
      • Closest to earth.
      • Hottest planet. (97% co2)
      • Slightly smaller than earth. (500 km in dia)
      • Rotates east to west unlike others.
      • No satellite.
      • Rotation period – 257 days. (slowest)
      • Revolution period – 224.7 days.
      • Transit of venus – When it passes directly between the sun and earth, 8 year apart but separated by a century. Last was in 2004, next will be in 2117.
    • Mars
      • Revolution period – 687 days.
      • Rotation period – 24.6 hours.
      • Satellites – phobos and deimos.
    • Jupiter
      • Almost 11 times of earth.
      • Also called lord of the heavens.
      • Rotation period – 9.8 hrs. (fastest)
      • Revolution period – 12 years.
      • Have 16 satellites. (prominent are europa, ganymede and callisto)
      • Ganymede is the largest satellite.
      • Europa resembles living conditions.
    • Saturn
      • Least density – 30 times less than earth.
      • Revolution period – 29 years.
      • Rotation period – 10.3 hours.
      • More than 39 satellites. (prominent is titan)
      • Have system of rings. (three well defined)
    • Uranus
      • Identified as a planet in 1781 by William hershal.
      • Rotates from north to south as it is inclined at an angle of 98 degree to its orbit.
      • Revolution period – 84 years.
      • Rotation period – 16.8 hours.
      • Surrounded by 9 faint rings.
      • Have 21 satellites. (Miranda, aricl etc.)
    • Neptune
      • Greenish star because of methane.
      • Revolution period – 165 years.
      • Rotation period – 16.18 hours.
      • Notified by J g galle of Berlin in 1846.
      • Prominent satellites are trion and neroid.
    • Uranus and Neptune are called jovion twins.
    • Brightest star – Sirius. (dog star)
    • Comet
      • May have originated from a huge cloud, the oort cloud.
      • Solid matter combined with gases.
    • Asteroids
      • Or minor planets between mars and jupiter.
      • Also called planetoids or small planets.
      • Chunks of rock covered in frozen gases.
    • Meteroids are smaller than asteroids. (mostly are smaller than the size of pebble)
    • Meteor is a meteroid that has entered the earth atmosphere. (shooting/falling star)
    • A meteorite is as meteor that has fallen to earth.
    • The moon
      • 59% of surface is visible from earth.
      • Revolution period – 27 days 7 hrs 43 min 11.47 sec.
      • Rotation period – 27 days 7 hrs 43 min 11.47 sec.
      • Circumference – 11,000 km.
      • Distance from earth – 3, 82,200 km.
      • Moon light takes 1.3 sec to reach earth.
      • New moon = no moon. (moon is between earth and sun)
      • Full moon = complete moon. (occurs every 14th day after new moon)
      • Two full moons in a single month, then second full moon is called a blue moon.
    • Stars
      • Due to novae and supernovae explosion a star will turn into a neutron star or pulsar.
      • Color indicates the temperature of its surface: – blue color (max temp.) > yellow > red.
      • Evolutionary sage of a star: – adult star > red giant > white dwarf.
    • Earth
      • Circumference
        • Polar – 40008 km.
        • Equatorial – 40075 km.
      • Area – 510 million sq km.
      • 5th largest planet.
      • Perigee (nearest position of earth to moon) – 3, 56,000 km.
      • Apogee (farthest position of earth to moon) – 4, 07,000 km.
      • Aphelion (farthest position of earth from sun) on 4th july about 152 million km.
      • Perihelion (nearest position of earth to sun) on 3rd jan about 147 million km.
    • History of earth is studied in terms of geological years, periods and epochs.
    • Earth is an oblate spheroid (bulges at the equator and flattened at the poles), also called geoid.
    • At poles weight will be more.
    • Geodesy is a branch of science which deals with measuring the earth’s size and shape.
    • Equinoxes (sun is vertically overhead at the equator)-
      • 21st march – vernal equinox.
      • 23rd September – autumnal equinox.
    • Age of earth – 4.5 to 4.6 billion years.
    • Earth’s circumference at equator – 24901.55 miles (40075.16 km).
    • Earth’s circumference between the poles – 24859.82 miles (40008 km).
    • Earth’s diameter at the equator – 7926.28 miles (12756.1 km).
    • Lowest elevation on land – dead sea 1369 ft (417.27 m) below sea level.
    • Deepest point in the earth – mariana trench in western Pacific Ocean (10994 m).
    • Highest temperature recorded – 134.0 0 F in death valley, California (USA) on 10th july,1913.
    • Lowest temperature recorded – 128.5 0 F in vostok, Antarctica on 21st july,1983.
    • 21st june (summer solstice)
      • Longest day in northern hemisphere.
      • Shortest day in southern hemisphere.
      • Sun is vertically overhead at the tropic of cancer.
    • 22nd december (winter solstice)
      • Longest day in southern hemisphere.
      • Shortest day in northern hemisphere.
      • Sun is overhead at the tropic of capricorn.
    • 21st march and 23rd September – equal day and night in both the hemispheres.
    • Rotation of earth
      • It takes 23 hrs 56 min 40.91 sec (approx. 24 hrs).
      • Speed is max at equator – 1667 km/h ; and min at poles – 0 km/h.
    • At equator day and night are equal.
    • Effect of rotation of earth
      • Causation of day and night.
      • Change in direction of winds and ocean currents.
      • Rise and fall of tides.
      • Difference of 1 hour between the two meridians which are 15 0 apart.
    • Division of day and night is considered by the circle of illumination.
    • Revolution of the earth
      • It takes 365 days 5 hours 48 min 45.51 sec (approx. 365¼ days).
    • Effect of revolution of the earth
      • Change of seasons.
      • Variation of length of day and night.
      • Shifting of wind belts.
    • Seasons
      • Spring: When the sun is directly overhead the equator (21st march).
      • Summer: When the sun is directly overhead the tropic of cancer, the North Temperate Zone experiences summer (21st june).
      • Autumn: When the sun returns to the equator, the North Temperate Zone experiences the season of autumn (23rd september).
      • Winter: The sun is at the tropic of Capricorn, the North Temperate Zone experiences winter (22nd dec).
    • 1 0 latitude = 111 km.
    • Some important latitudes are
      • Equator – 0 0.
      • Tropic of cancer – 23½ 0
      • Tropic of Capricorn – 23½ 0
      • The Arctic Circle – 66½ 0
      • The Antarctic Circle – 66½ 0
    • In 1884, it has been decided that the zero meridian is one that passes through the royal astronomical observatory at Greenwich near London.
    • 180 0 meridian (International Date Line) is exactly opposite to the prime meridian (such points are called antipodal points).
    • 5 0 East meridian is the standard time meridian of our country, it is 5 hrs 30 min ahead of the Greenwich mean time (GMT) and is situated at Naini near Allahabad.
    • The earth is divided into 24 longitudinal zones, each being 15 0 or 1 hrs apart in time or 1 0 in four minutes are called standard time zones.
    • Russia has as many as 11 time zones.
    • Both USA and Canada have five time zones viz. the Atlantic, eastern, central, mountain and pacific.
    • International date line:- the 1800 meridian running over pacific ocean deviating at Fiji, Samoa and Gilbert islands. (deviates at land masses)
    • While crossing date line from west to east – repeats a day.
    • While crossing date line from east to west – losses a day.
    • Generally a total of seven eclipses (including solar and lunar eclipse) take place in a year.
    • Solar eclipse (moon comes between) –
      • It can be partial or total.
      • Happen only on a new moon day.
      • But it doesn’t occur in every new moon day.
    • Lunar eclipse (earth comes between) –
      • Happens only on a full moon day.
      • But not on every full moon day.
    • Structure of earth’s interior
      • The crust.
        • Thinnest layer.
        • Least density.
        • Thickness varies from 8 km to 40 km.
        • The rocks are rich in lighter minerals like Si and Al.
        • Layer is also called Sial.
        • Average density = 2.7 gm/cm3.
      • The mantle.
        • About 2900 km in thickness.
        • Minerals are in semi solid state.
        • Upper mantle (Asthenosphere) is about 250 km thick.
        • Layer is also called Sima.
        • Average density = 5.68 gm/cm3.
      • The core.
        • The innermost layer.
        • 3500 km in radius.
        • Also known as Nife.
        • Average density = 17.2 gm/cm3.
      • Discontinuities: The various layers are separated by discontinuities, which are advent in seismic data.
Crust Upper crust
Connard discontinuity
Lower crust
Mohorovic discontinuity
Mantle Upper mantle
Repetti discontinuity
Lower mantle
Gutenberg discontinuity
Core Upper core
Lehman discontinuity
Lower core

 

  • Composition of earth
    • Sulphur – 1.9%.
    • Iron – 35%.
    • Oxygen – 30%.
    • Silicon – 15%.
    • Maganese – 13%.
    • Nickel – 2.4%.
  • Composition of earth’s crust
    • Oxygen – 46%.
    • Silicon – 28%.
    • Aluminum – 8%.
    • Iron – 6%.
    • Maganese – 4%.
    • Calcium – 2.4%.
    • Potassium – 2.3%.
    • Sodium – 2.1%.
  • Plate tectonics theory
    • Describe the large scale motion of lithosphere.
    • States that lithosphere is divided into several rigid segments called plates, it includes both oceanic and and continental crusts.
    • Plates moves on asthenosphere. (solid which flows under stress)
    • About 20 such plates are identified.
    • Seven major plates are:
      • Eurasia.
      • Antarctica.
      • North America.
      • South America.
      • Pacific.
      • African.
      • And Indian plate.
    • Various intermediate size plates such as:
      • China.
      • Philippine.
      • Arabian.
      • Iran.
      • Nazaca.
      • Cocos.
      • Caribbean.
      • And Scotia plates.
    • Depending upon the type of movement, plate margins are
      • Divergent margin. (constructive)
        • Plate moves apart with upwelling from mantle.
        • Formation of mid oceanic ridges.
        • Example: Surtsey Island along with mid Atlantic ridges.
      • Convergent margin. (destructive)
        • Two plates collide, one plate bending downward and subducting below the other.
        • Formation of deep oceanic trench and Fold Mountains.
        • Example: Himalayan boundary fault, Pacific ring of fire etc.
      • Parallel plate margin. (constructive/tansform boundary)
        • Plates slides past one another without the creation or destruction of crust.
        • Example: San Andreas Fault along western cost of USA (Mexico) is a famous transform fault.
  • Continental drift theory
    • By Alfred Wagener in 1915.
    • About 250 million year ago, only one continent (Pangea) and one mass of water body (Panthalassa) was there.
    • Breaking process started about 200 million year ago.
    • Northern rift cuts Pangaea from east to west creating Eurasia in the north and Gondwanaland in south. A shallow sea called Tethys was situated between.
  • Earthquakes
    • Caused by endogenetic forces.
    • Magnitude or intensity of energy released is measured by Richter scale.
    • Damage caused is measured by modified Mercalli intensity scale.
    • Study is known as seismology.
    • Seismic waves are of three types:
      • Primary waves.(P waves)
        • Shorter wavelength and higher frequency.
        • Longitudinal waves.
        • Can travel through solid, liquid and gas.
      • Secondary waves.(S waves)
        • Shorter wavelength and higher frequency.
        • Transverse wave.
        • Travels through all solid particles.
      • Surface waves or long waves.(L waves)
        • Waves of long wavelength, confined to the skin of the earth crust.
        • It causes most of the structural damage.
    • Homoseismal lines: Imaginary lines where waves arrives at the same time.
  • Eurasian plate is static while Indian plate is moving south to north at 5 cm/year.
    • Due to this earthquake occurs in Himalayan region, and height of Himalayas is increasing at the speed of 1 cm/year.
  • Most of the world earthquakes occur in
    • The zone of young fold mountain.
    • The zone of folding and faulting.
    • Zones of junction of continental and oceanic margin.
    • Zones of active volcanoes.
    • Along different plate boundaries.
  • Traditional zones of earthquakes
    • Circum Pacific belt.
    • Mid Continental belt.
    • Mid Atlantic belt.
  • Volcanism
    • Several integrated processes such as gradual increase in temperature with the depth, due to the heat generated by degeneration of radioactive elements inside the earth.
    • Origin of magma due to the lowering of the melting point caused by reduction in pressure of overlying rocks due to fractures caused by splitting of plates.
  • Classification of volcanoes
    • On the basis of mode of eruption:
      • Central eruption or explosive type.
        • Example: Hawaiian type, Strombolian type, Pelean type, Visuvious type, volcanic type etc.
      • Fissure eruption or quiet eruption.
        • Successive flow of lava results in the growth of lava plateau. Example: Deccan plateau etc.
    • On the basis of periodicity of eruption:
      • Active volcano.
        • Erupts periodically.
        • Example: Etna, Stromboli, Mayon etc.
      • Dormant volcano.
        • Volcano which becomes quiet after its eruption for some time.
        • Example: Fujiyama, Krakatoa, Barren Island etc.
      • Extinct volcano.
        • No indication of future eruption.
  • Various volcanic belts
    • Circum pacific belt.
      • Fire girdle of the pacific or the fire ring of the pacific.
      • It extends across the Kamchatka peninsula, Kurile Islands, the islands of Japan, Philippines, New Guinea, New Zealand and the soloman islands.
    • Mid continental belt.
      • Volcanic zones of convergent continental plate margins.
      • Includes volcanoes of alpine mountain chain, the Mediterranean sea and the fault zone of eastern Africa of Stromboli, Vesuvius, Etna, Kilimanjaro.
    • Mid Atlantic belt.
      • Fissure eruption type.
      • Example: Iceland, Canary Islands, Cape Verde, Azores etc.
  • Highest volcanic peaks are Cotopaxi (South America), Fujiyama (Japan) and Valley of Ten Thousand Smokes (Alaska).
  • Weathering
    • Physical weathering.
      • Factors are temperature change, Crystallization of water into ice, the pressure release mechanism etc.
    • Chemical weathering.
      • Factors are solution, oxidation, carbonation, hydration, hydrolysis and chelation.
    • Biological weathering.
      • Three types Faunal, Floral and Anthropogenic.
  • Rocks (can be defined as an aggregate of minerals).Depending upon the process of their formation
    • Igneous rocks / Primary rocks.
      • Formed due to the cooling, solidification and crystallization of hot and molten magma.
      • Believed that they are formed during each period of geological history of the earth.
      • Are hard, granular and crystalline rocks.
      • Less affected by chemical weathering.
      • It does not have any fossil or does not form any strata or layers of lava.
      • Classification of igneous rocks
        • On the basis of mode of occurrence
          • Intrusive rocks.
            • Formed due to solidification of rising magma below the surface of the earth.
            • Example: Granite, Lapolith, Batholiths, Sills etc.
          • Extrusive rocks.
            • Formed due to cooling and solidification of hot and molten magma at the earth surface.
            • Example: Basalt, Gabbro etc.
        • On the basis of silica content
          • Acidic.
            • Has more silica content. Example: Granite.
          • Basic.
            • Has less amount of silica content. Example: Gabbro.
    • Sedimentary rocks.
      • Formed due to the aggregation and compaction of sediments derived from the older rocks, plants, animals and contains fossils of plants.
      • Can be classified on the basis of the nature of sediments
        • Mechanically formed rocks.
        • Chemically formed rocks.
        • And organically formed rocks.
    • Metamorphic rocks.
      • Changed form of igneous and sedimentary rocks.
      • Are the rocks which change either in form or composition without disintegration.
      • Are metamorphosed.
      • Agents of metamorphism are heat, compression and solution.
Original rocks Metamorphic rocks
Limestone Marble
Sandstone Quartzite
Shale/Clay Slate, Phyllite, Schist
Coal Diamond/Graphite coal
Granite Gneisse
  • Various landforms are mountains, hills, plateaus and plains.
  • Mountains (based on their mode of formation) –
    • Fold mountains.
      • Formed due to the compressive forces generated by endogenetic forces. (Earthquake, landslide etc.)
      • On the basis of age fold mountains are
        • Young / New fold mountains.
          • Formed after continental drift.
          • Example: Himalayas, Alps, Andes, Rockies, Atlas etc.
        • Old mountains.
          • Are of pre-drift era, and then subjected to denudation and uplift.
          • Example: Pennines (Europe), Appalachians (USA), Aravallis (India) etc.
    • Block mountains.
      • Huge blocks raised or lowered.
      • Raised part is known as horsts and lowered part rift valley / Graben.
      • Example: Narmada, Tapi and Damodar valley, the Vosges in France and Black forest in Germany (Rhine river flows).
    • Volcanic mountains / Mountains of accumulation.
      • Example: Mount Fiji (Japan), Cotopaxi (Andes), Vesuvius and Etna (Italy), Mount Mayon (Philippines) etc.
    • Residual or Dissected mountains.
      • Result of erosion of plateaus and high planes.
      • Example: Girnar and Rajmahal (India), Catskill (New York), Sierras (Spain) etc.
  • Plateaus (relief of more than 500 ft). According to their mode of formation and their physical appearance
    • Tectonic plateau.
      • Formed by the earth’s movement which causes uplift and are normally of a considerable size and fairly uniform altitude.
      • Plateau which is enclosed by Fold Mountains is known as intermount plateau.
      • Example: Tibetan plateau (Himalayas), Kunlun and Bolivian plateau.
    • Volcanic plateau.
      • Formed by the accumulation of lava.
      • Example: Deccan plateau of India.
    • Dissected plateau.
      • Formed by the continuous process of weathering and erosion.
      • High extensive plateau are gradually worn out and there surface made irregular.
      • Example: Scottish highlands.
  • Plains
    • Low lying and flat land surface with least difference between its highest and lowest point.
    • Types of plains.
      • Structural plains.
        • Example: great Plains of USA.
      • Erosion plains.
        • Example: Plains of north Canada.
      • Depositional plains.
        • Example: Indo- Ganga plain.
  • Islands
    • A grouping of geographically or geologically related islands is called an archipelago.
    • According to the way they are formed they are classified as.
      • Continental Island.
        • Rests on the continental shelf.
        • Water level around is very shallow, typically less than 600 ft.
        • Example: Canadian island, Green land, Great Britain etc.
      • Volcanic Island.
        • When volcanoes deep in the ocean rises, forms a volcanic island.
      • Coral Island.
        • Forms a ring and partially or totally encloses a shallow body of water or lagoon.
        • Have large collection of coral at top rock (usually volcanic) in the ocean.
        • Example: Lakshadweep.
      • Alluvial Island.
        • Are formed by the outward flow of water depositing silt and gravel at the mouth of the river.
        • Example: New Moore Island (West Bengal).
      • Barrier Island.
        • Formed by the waves depositing sand on the shallow ocean bottom as they crash on the shoreline.
      • Tectonic Island.
        • Long island arcs (archipelago) are formed.
        • Example: Indonesia, Philippines, Japan etc.
  • Lakes
    • Tarn Lake / Alpine Lake.
      • Associated with glacial regions. (areas glaciated in past)
      • Forms cirque.
      • Example: Along the slopes of Adirondack mountain (from the last ice age), along European Alps (recent glaciations) etc.
    • Rift Valley Lake.
      • Occurs in areas where rocks are pulling apart.
      • Example: Nyasa (The rift valley which cuts through Asia and Africa, contains the largest group of such lakes) etc.
    • Crater Lake.
      • Forms at a volcanic peak, when an extinct volcano collapses.
      • Example: Lake of Oregon.
    • Deflation Lake.
      • Usually occurs in deserts.
      • Wind blows out depressions in the sand creating Oasis.
    • Oxbow Lake.
      • Formed by curved river meander that was cut off by sediments or other means, creating a bowed shaped lake.
      • Example: at Mississippi river.
    • Artificial Lake.
      • Damming of a river.
  • Fluvial landforms
    • Feature resulting from the movement of water on the earth surface. The two types of landforms made are:
      • Erosion landforms.
        • Example: U shaped valley, Potholes, Meanders, River terraces, Plunge pools etc.
      • Depositional landforms.
        • Example: Alluvial plains, Deltas, Flood plains, Natural levees, Point bars etc.
  • Karst landforms
    • Any limestone or dolomite region showing typical landforms produced by the action of ground water, through the process of solution and deposition. The two types of landforms made are:
      • Erosion landforms.
        • Example: Pools, Sinkholes, Lapis and Limestone pavement, Caves etc.
      • Depositional landforms.
        • Example: Stalactites, Stalagmites, Pillars etc.
  • Glaciers
    • Mass of ice moving at a speed of approx. 15 to 18 m per day.
    • Formed at high altitude due to too low temperature and high aerographic precipitation.
    • Glaciers moves basically due to force of gravity.
    • Generally two types of landforms are made by glaciers:
      • Erosion landforms.
        • Example: Cirque / Corrie, U shaped valley, Horns, Glacial troughs, Hanging valley etc.
      • Depositional landforms.
        • Example: Moraines, Eskers, Outwash plains, Drumlins etc.
  • Coastal landforms
    • Formed through sea waves, aided by current tides and storms in coastal areas.
    • Coastal processes are the most dynamic and destructive.
    • The two types of landforms made by sea and oceanic waves are:
      • Erosion landforms.
        • Example: Cliffs, Terraces, Caves, Stacks etc.
      • Depositional landforms.
        • Example: Beaches, Dunes, Bars, Barriers, Splits etc.
  • Aeolian Landforms
    • Regions where erosion and deposition by wind are dominant geomorphic forces in shaping the landforms.
    • Are formed in hot deserts, coastal zones and fields.
    • The two types of Aeolian landforms are:
      • Erosion landforms.
        • Example: Pediments, Pedi plains, Playas, Deflation hallows, Cave mushroom rock, Table rock, Pedestal rocks etc.
      • Depositional landforms.
        • Example: Sand dunes, Barchans, Seifs etc.
  • Significance of atmosphere
    • Acts as a filter as it absorbs the various unwanted radiation.
    • Source to various gases.
    • Supports life form in biosphere.
  • Extent of atmosphere
    • Almost 97% of effective atmosphere confines within 29 km of the earth’s surface.
    • Distribution is not uniform and even not homogeneous.
    • It extends to 16-29,000 km from the sea level.
    • Atmosphere = gases + vapours + particulates
  • Layers of atmosphere
    • Troposphere.
      • Extends up to 16 km.
      • Thickness varies from 8 km at poles to 18 km at equator.
      • Normal lapse rate of temperature, 10C drops at every 165 m (or 6.40C / km).
      • Accounts for practically the entire water vapour, all dust particles and most of the CO2.
      • All weather phenomenons such as condensation, precipitation and storms etc. occurs in this layer.
    • Tropopause.
      • Separates troposphere from stratosphere..
    • Stratosphere.
      • Extends up to 50 km.
      • Temperature increases with height. (temperature inversion)
      • Temperature range, -600C at tropopause to 00C at stratopause.
      • Contains ozonosphere.
      • Free from dust particles and atmospheric turbulences, thus ideal for jet aircrafts
    • Stratopause.
      • Separates stratosphere and mesosphere.
    • Mesosphere.
      • Extends up to 80 km.
      • Temperature decreases with height, 00C to -1000
      • Coldest layer of atmosphere.
    • Mesopause.
      • Transitional layer between mesosphere and ionosphere.
    • Ionosphere.
      • Extends up to 600 km.
      • Contains electrically charged ions which reflects radio waves back.
      • Absorption of solar radiations causes temperature increase with height.
      • Due to ion concentration it acts as a protective layer against meteorites that are burnt in this layer.
    • Thermosphere.
      • Zone between 85 km to 400 km above the surface.
      • Temperature rises with altitude.
    • Thermopause.
      • It is the upper limit of thermosphere.
      • At an altitude of about 600 km.
      • Day temperature exceeds 14000C while night 2250
      • Contains lighter gases like hydrogen and helium.
    • Exosphere.
      • Outer most part of the atmosphere.
      • Extends up to 900 km.
      • Upper limit acts as transitional layer between atmosphere and space.
    • Magnetosphere.
      • Outer part of the exosphere.
      • Presence of air is extremely rare..
  • Insolation
    • Solar radiation that is intercepted by earth.
    • Amount of insolation depends on:
      • Area and nature of surface.
      • Inclination of the rays of the sun.
      • Distance between earth and the sun.
      • Length of the day.
      • Transparency of the atmosphere.
  • Albedo – Portion of solar radiation reflected from the surface.
  • Heat budget of the earth / Heat balance – Mechanism of maintaining the same temperature by the atmosphere.
  • Terrestrial radiation – Process in which heated surface of the earth radiates energy in the form of long waves.
  • Atmospheric pressure
    • Air is extremely compressible gas.
    • It is neither the same for all the regions nor the same for one region all the time.
  • Factors affecting atmospheric pressure
    • Altitude: Pressure increases when air descends, due to the decrease in volume.
    • Temperature: Pressure rises with decrease in temperature.
    • Earth rotation.
  • Pressure belts
    • Equatorial low pressure belt. (doldrums)
      • Zone extending between 50N and 50
      • Not stationary i.e seasonal drift of this belt with summer and winter solstice.
      • It is thermally induced.
      • Represents the zone of convergence of northeast and southeast trade winds.
      • Due to frequent calm conditions, known as belt of calm or doldrums.
    • Inter tropical convergence zone. (ITCZ)
      • Low pressure belt at equator where trade winds converge hence here air tends to ascend.
      • In July it is around 200N – 250N latitude (over the Gangetic plane), sometimes called the monsoon trough. It encourages thermal low over north and north-west India.
      • Due to shift of ITCZ trade winds of the southern hemisphere cross the equator between 400E and 600E longitude, and starts flowing from south-west to north-east due to the Coriolis force. It becomes south-west monsoon.
      • In winter the ITCZ moves southwards and so the reversal of winds to south and south-west, takes place, they are called north-eastern monsoons.
    • Sub tropical high pressure belt.
      • 300 – 350 in both hemispheres.
      • The high pressure along this belt is due to subsidence of air coming from equatorial regions and also due to blocking effect of Coriolis force.
      • The convergence of winds at high altitudes above this zone results in the subsidence of air from the higher altitudes.
      • Thus descent of wind results in concentration of their volume and ultimately causes high pressure.
      • This zone of high pressure is also called Horse latitude.
    • Sub polar low pressure belt.
      • 600– 650 in both the hemisphere.
      • Does not appear to be thermally induced as there is low temperature throughout the year and as such there should have been high pressure belt instead of low pressure belt, thus it is dynamically induced.
      • More developed at southern hemisphere (and regular) because of the over dominance of water.
    • Polar high pressure belt.
      • High pressure persists at the poles throughout the year.
      • Are small in area.
  • Shifting of wind belts
    • The entire system of pressure and wind belts follows the movement of mid day sun.
      • In June when the overhead sun is above Tropic of Cancer, all the belts move about 50-100 north of their average position.
      • In the same manner when the sun is at Tropic of Capricorn in December, the entire belt swings 50-100 south of their average position.
  • Wind system
    • Pressure difference is the major cause of the genesis of the wind system.
    • Slope of pressure from high to low is called as Pressure gradient, also called Barometric slope.
    • Imaginary lines joining the points having same pressure is called Isobars. The direction of air movement should be perpendicular to isobars as direction of Pressure gradient is perpendicular to isobars, but it is deviated from the expected one due to Coriolis force caused by the rotation of the earth.
  • Wind direction and the related laws
    • Because of Coriolis force all the winds are deflected to the right in the northern hemisphere while they are deflected to the left in the southern hemisphere, with respect to the rotating earth. This is reoffered to as Farrel’s law.
    • The Coriolis force is absent along the equator but increases progressively towards the poles.
  • Types of winds
    • Permanent winds.
      • Trade winds.
        • Steady current of air blowing from sub-tropic high pressure belt towards the equatorial low pressure belt.
        • Under the influence of the Coriolis force they flow from the north-east in the northern hemisphere and from south-east in the southern hemisphere.
      • Westerlies.
        • Blows from sub tropic high pressure belt towards the sub polar low pressure belt in both the hemispheres.
        • General direction is south-west to north-west in northern hemisphere and north-west to south-east in the southern hemisphere.
        • They are best developed between 400-650 S latitude.These latitudes are often called Roaring forties, Furious fifties and Shrieking sixties.
      • Polar winds.
        • Blows from polar high pressure belt towards the sub polar low pressure belt.
        • Are north easterly in northern hemisphere and south easterly in southern hemisphere.
    • Seasonal winds.
      • Reverses its direction completely in duration of every six months.
      • Example: Monsoon winds etc.
    • Local winds.
      • Is horizontal movement of winds on small scale.
      • Movement is mainly caused by the local factors such as water body, mountain etc.
      • They may be hot, cold, dry or warm.
      • Example: Land breeze (warm), Sea breeze (cold), Chinook (warm), Loo (hot/dry), Kalbaisakhi/Bardoli chheerha (hot) etc.
  • Cyclones
    • Low pressure surrounded by closed isobars having increased pressure outward and closed air circulation from outside towards the central low pressure.
    • Air blows inward in anticlockwise direction in the northern hemisphere.
    • Air blows inward in clockwise direction in the southern hemisphere.
    • Cyclone are mainly of two types:
      • Tropical cyclone.
        • Have thermal origin.
        • They acquire whirling motion due to coriolis force.
        • Wind speed varies from 0 km/h to 1200 km/h.
      • Temperate cyclone.
        • Develop over mid latitudes, range 350 to 650 N and S.
        • They are also called Extra tropical or Wave cyclones.
        • Example: Typhoons (China sea), Tropical cyclones (Indian ocean), Tornadoes (USA) etc.
  • Anticyclones
      • High pressure at centre and low pressure at the outer margins surrounded by circular isobars where wind blows.
      • Wind blows center to outward in clockwise direction in the northern hemisphere.
      • Wind blows centre to outward in anticlockwise direction in southern hemisphere.
      • Are high pressure systems, common in sub-tropical belt and practically absent in the equator region.
      • Generally associated with rainless fair weather and that’s why they are called as Weatherless phenomena.
  • Thunderstorms
    • Are local storms, characterized by swift upward movement of air and heavy rainfall with loud thunder and lightning.
    • Structurally a thunderstorm consists of several convective cells which are characterized by strong updraft of air.
  • Tornado
    • Very strong tropical cyclones of smaller size.
    • In Mississippi valley (USA) they are called twisters.
    • More destructive than cyclones.
    • Sometimes speed exceeds 320 km/h.
  • Jet streams
    • The strong and rapidly moving circumpolar westerly air circulation in a narrow belt of a few 100 km width in the upper limit of troposphere is called Jet stream.
    • Their circulation path is wavy and meandering.
    • Extent of jet streams narrows down during the summer season because of their northward shifting while these extends up to 200 North latitude during winter season.
  • Humidity
    • Humidity capacity.
      • Capacity of air of certain volume at certain temperature to retain maximum amount of moisture content.
    • Absolute humidity.
      • Total weight of moisture content per unit volume of air at definite temperature.
    • Specific humidity.
      • Mass of the water vapors (grams) contained in a kg of air.
      • It represents the actual quantity of moisture present in a definite volume.
    • Relative humidity.
      •  (Absolute humidity / Humidity capacity) *100
  • Dew point – When relative humidity reaches 100%, the air is completely saturated. That air temperature is said to be the Dew point.
  • Fog
    • Made from the droplets of water suspended in the lower of the atmosphere.
    • It is not considered as the form of precipitation.
    • Visibility of less than 1 km.
  • Smog = Smoke +Fog.
  • Haze
    • Formed by the water particles that have condensed in the atmosphere.
    • Visibility lies between 1 km – 2 km.
  • Frost – Is the moisture on the ground that condenses directly into ice. (condensation below freezing point)
  • Clouds
    • Mass of small water droplets or tiny ice crystals.
Latin names There meaning
Cirrus Like feather, Very high clouds
Cumulus Like heap, Flat base and rounded top
Stratus Lying in level sheets, Layer type
Alto High
Nimbus Rain clouds
  • Classified according to their appearance, form and height:
    • High clouds. (6000 m to 12000 m)
      • Cirrus.
        • Contains small ice crystals.
        • White wispy and fibrous appearance.
      • Cirro Cumulus.
        • Contains ice crystals.
        • Rippled in appearance.
      • Cirro Stratus.
        • Appears like a thin white almost transparent sheet.
    • Middle clouds. (2100 m to 6000 m)
      • Alto Cumulus.
        • Contains droplets in layers and patches.
      • Alto Stratus.
        • Contains droplets forming sheets of grey or watering looking clouds.
    • Low clouds. (below 2100 m)
      • Strato Cumulus.
        • Large globular masses.
        • Bumpy looking.
        • Soft and grey in appearance.
        • And regular or wavy pattern.
      • Nimbo Stratus.
        • Dark grey and rainy looking.
        • Dense and shape less.
        • Often gives continuous rain.
      • Stratus.
        • Are low grey and layered.
        • Fog like in appearance.
        • Brings dull weather accompanied by drizzle.
    • Clouds with great vertical extent. (1500 m to 9000 m)
      • Cumulus.
        • Round top flat base.
        • A whitish grey globular mass.
        • Consists of individual cloud units.
      • Cumulo Nimbus.
        • Great vertical extent.
        • White or black globular masses.
        • Brings conventional rain and thunder.
  • Precipitation
    • Classified on the basis of its origin.
      • Conventional rainfall.
        • Occurs due to thermal conventional currents caused due to insolational heating of ground surface.
        • Example: Congo basin, Amazon basin, South-east Asia etc.
      • Orographic rainfall.
        • Caused due to ascent of air forced by mountain barrier.
        • Example: Mahabaleshwar, Western Ghats (600 cm rainfall) etc.
      • Frontal rainfall.
        • Due to upward movement of air caused by convergence of cold air masses against warm air masses.
        • Example: North-west Europe (due to convergence of cold continental and warm oceanic air) etc.
  • Weather – Temperature, Pressure, Wind, Moisture, Cloudiness, Precipitation and Visibility at any given time.
  • Climate
    • Average weather over a large area.
    • Factors controlling weather and climatic conditions are:
      • Latitude.
      • Altitude.
      • Unequal distribution of land and water.
      • Ocean current.
      • Air pressure.
      • Wind.
      • Mountain barrier.
      • Nature of ground surface.
      • Atmospheric storms etc.
    • Different climate zones of the earth are:
      • Equatorial zone.
      • Hot zone.
      • Warm temperate zone.
      • Cool temperate zone.
      • Cold zone.
  • Composition of hydrosphere.
Storage component Total % of water
Oceans 97.6
Saline lakes and inland seas 0.008
Ice caps and glaciers 1.9
Ground water 0.5
Soil moisture 0.01
Lakes 0.009
Fresh water rivers 0.0001
Atmosphere 0.0009

 

  • Relief features of the oceans
    • Continental shelf.
      • Shallow submerged extension of the continent.
      • Extends to a depth of 180 m.
      • Average width – 70 km.
      • Slope of – 10 / mile.
      • Covers 7.5% of the Oceans. (Atlantic Ocean – 13.3%, Pacific Ocean – 5.7%, Indian Ocean – 4.2% etc.)
      • 20% of petrol and gas is found here.
      • Provides the richest fishing grounds.
    • Continental slope.
      • Extends seawards from the continental shelf.
      • Max depth up to – 3660 m.
      • Average slope – 200 to 500.
      • Andesite line – Boundary between continental shelf and continental slope.
      • Covers 8.5% of the ocean area.
    • Continental rise.
      • At the foot of the continental slope, due to the accumulation of debris transported over the slope.
      • Average slope – 0.50 to 10.
      • Oil deposits occur here.
    • Deep sea planes. (Abyssal)
      • Most extensive part of the oceanic floor.
      • Average depth – 3000 m to 6000 m.
      • Covers 75.9% oceanic area.
      • Occupied by raised ridges or submarine mountains and by very deep trenches or canyons.
    • Deeps. (Trenches)
      • Are narrow and steep side’s depressions.
      • Are formed when two plates moving together and one being pushed below the other.
      • Marina trench (Challenger deep) is the deepest trench at north-west Pacific Ocean near Philippines (approx 11 km deep).
    • Volcanic ridges.
      • Are of tectonic origin.
      • Formed by the volcanic activity along the spreading boundary of the plates.
      • These are thousands of km long and hundreds of km wide.
      • Their summits may rise as Islands. Example: Iceland, Azores Island etc.
  • Coral reefs
    • Formed due to the accumulation and compaction of skeletons of lime secreting organisms (Coral polyps).
    • Found mainly in the tropical oceans and seas as they require high mean annual temperature. (200 C to 250 C)
    • Do not lies in deep sea water, due to lack of sunlight and oxygen.
    • On the basis of nature, mode of occurrence and shape, Coral reefs are classified into three types:
      • Fringing reefs.
        • Develops along continental margins or along the islands.
        • Seawards slope is steep and vertical, while landwards slope is gentle.
        • Runs as a narrow belt of about 0.5 km to 2.5 km width.
        • Usually attached to the coastal land but occasionally they are separated from the shore by a shallow and narrow lagoon (Boat channel).
        • Example: Near Rameshwaram in the Gulf of Mannar, etc.
      • Barrier reefs.
        • Largest coral reefs off the coastal platform, but parallel to them.
        • A broad lagoon develops in between the reef and the shore.
        • Are hundreds of km long and a few km wide.
        • Example: Great Barrier Reef of Australia (largest), etc.
      • Atoll.
        • A reef of narrow growing corals of horse shoe shape and crowned with palm trees.
        • Partly or completely encloses a lagoon.
        • Formed around an island or in an elliptical form on a submarine platform.
        • Example: Funafuti atoll of Ellice Islands, etc.
  • Coral bleaching – When chorals are stressed by changes in conditions such as temperature, light or nutrients, they expel the symbiotic algae living in there tissues causing them to turn colourless.
  • Salinity
    • Total amount of salts and minerals in grams contained in 1 kg of sea water, expressed as part per thousand.
    • Affects marine organism and plant community, also physical properties of ocean such as temperature, pressure, density, waves and currents.
    • Average salinity: 35 mg / kg. (35 ppt)
    • Average salinity in southern hemisphere > average salinity of the northern hemisphere.
    • Iso halines: Represents the salinity distribution on the surface of the sea. (lines joining places having an equal degree of salinity)
    • Due to dissolution of rocks of oceanic crust.
    • Variation of salinity causes vertical circulation of water.
    • More saline water freezes slowly and the boiling point is higher than the fresh water.
    • Decreases from equator to poles.
    • Highest salinity is near the tropics, because of heavy precipitation in the equatorial region.

 

Controlling factor Relation with salinity
Evaporation Greater evaporation higher the salinity
Precipitation Higher the precipitation lower the salinity
Influx of river water Salinity is reduced at the mouth
Atmospheric pressure Anti cyclonic conditions with stable air and high temperature

Increases the salinity of the surface water of the ocean

Circulation of oceanic water Ocean currents affects the spatial distribution of salinity by mixing sea waters

 

  • Ocean currents
    • Due to the action of breaking waves, wind, coriolis effect, temperature, salinity, shape and configuration of coast line and the tides (caused by sun and the moon).
    • Clockwise in northern hemisphere and anticlockwise in the southern hemisphere.
    • Are of two types:
      • Warm currents.
        • Flows from lower latitude to the higher latitude.
      • Cold currents.
        • Flows from higher latitude to the lower latitude.
  • Tides
    • Rises at an interval of approx 12 hrs 26 min.
    • The two major types of tides are:
      • Spring tides.
        • Occurs when earth, moon and sun are in line i.e straight line configuration of the three celestial bodies.
        • Sun enhances the gravitational pull of the moon, creating the condition of higher high tides and lower low tides.
      • Neap tides.
        • When the sun and the moon are at right angles to the earth.
        • The sun partially contracts the pull of the moon, producing lower high tides.

 

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