HomeGeneral KnowledgeWorld Geography Short notes part 2: Earth, Latitudes & Longitudes (Meridians), Eclipses...

World Geography Short notes part 2: Earth, Latitudes & Longitudes (Meridians), Eclipses Rocks Weathering Earthquakes Volcanoes Tsunami


  • The Earth is an oblate spheroid, nearly spherical with a slight flattening at the poles and a bulge at the equator.
  • Perihelion: Nearest position of the Earth to the Sun.
  • Aphelion: Farthest position of the Earth from the Sun.
  • The Earth’s interior consists of three major layers: the crust, the mantle, and the core.
  • Eduard Suess: Explained the Earth’s interior based on chemical composition as SIAL, SIMA, and NIFE.
    • SIAL (Silicon-Aluminium): Upper part of the crust.
    • SIMA (Silicon-Magnesium): Lower part of the crust.
    • NIFE (Nickel-Iron): Outer part of the core.
  • Rotation of the Earth: Spins on its imaginary axis from West to East in one day, causing day and night and affecting tides.
  • Revolution of the Earth: Motion in an elliptical orbit around the Sun in one year, resulting in the change of seasons.

Statistics Data of the Earth

  • Age: 4550 million years
  • Mass: 5.976×1024 kg
  • Volume: 1.083×1012 km³
  • Mean Density: 5.513 g/cm³
  • Total Surface Area: 510 million sq km
    • Land Area: 29.2% of the total surface area
    • Water Area: 70.8% of the total surface area
  • Rotation Speed: 23 hr, 56 min, and 4.100 sec
  • Revolution Speed: 365 days, 5 hr, and 45.51 sec
  • Dates when days and nights are equal:
    • March 21 (Vernal Equinox)
    • 23rd September (Autumnal Equinox)
  • Longest day: 21st June (Summer Solstice) – Sun is vertically overhead at Tropic of Cancer
  • Shortest night: 22nd December (Winter Solstice) – Sun is vertically overhead at Tropic of Capricorn
  • Escape velocity: 11.2 km/sec
  • Mean surface temperature: 14°C


  • Definition: Imaginary lines drawn on the Earth’s surface parallel to the equator.
  • Equator (0°): Divides Earth into two equal hemispheres (North and South).
  • Tropic of Cancer (23.5°N): Northernmost latitude where the Sun can be directly overhead.
  • Tropic of Capricorn (23.5°S): Southernmost latitude where the Sun can be directly overhead.
  • Arctic Circle (66.5°N): Marks the southernmost latitude where the Sun can remain continuously above or below the horizon for 24 hours.
  • Antarctic Circle (66.5°S): Marks the northernmost latitude where the Sun can remain continuously above or below the horizon for 24 hours.
  • Distance: Each degree of latitude equals approximately 111 km.

Longitudes (Meridians)

  • Definition: A series of semicircles that run from pole to pole passing through the equator.
  • Prime Meridian: Passes through Greenwich near London, dividing the Earth into Eastern and Western hemispheres (0°).
  • Function: Determines local time in relation to Greenwich Mean Time (GMT).
  • Time Difference: 1° change of longitude corresponds to approximately 4 minutes difference in time.

International Date Line (IDL)

  • Definition: It is the longitude where the date changes by exactly one day when it is crossed.
  • Location: The International Date Line is located at 180° longitude, both east and west.
  • Effect on Date: Crossing the International Date Line from west to east results in the addition of one day to the calendar, while crossing from east to west results in the subtraction of one day.
  • Samoa Island Shift: Samoa island decided to shift itself to the west side of the International Date Line in order to align its time zone more closely with its major trading partners, such as Australia and New Zealand.

Indian Standard Time (IST)

  • Calculation Basis: Indian Standard Time is calculated based on the 82.5°E longitude, which passes through several Indian states including Uttar Pradesh, Madhya Pradesh, Odisha, Chhattisgarh, and Andhra Pradesh.
  • Relation to GMT: IST is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT).
  • Rotation of Earth: The Earth completes one rotation in approximately 24 hours, corresponding to 360° of its rotation.
  • Significance: IST serves as the standard time reference for the entire country of India.


  • Solar Eclipse: Occurs when the Moon moves between the Earth and the Sun, blocking the sunlight and casting a shadow on the Earth. It can be partial or total, depending on the alignment of the Sun, Moon, and Earth.
  • Lunar Eclipse: Happens when the Earth passes between the Sun and the Moon, causing the Earth’s shadow to fall on the Moon. This results in the Moon appearing darkened or reddish in color, depending on the intensity of the eclipse.


Rocks are composed of minerals and are categorized into three main types:

  • Igneous Rocks: Formed from the solidification of molten magma. Examples include Mica and Granite.
  • Sedimentary Rocks: Created by the accumulation of rock particles and organic matter in layers under pressure. Examples include Gravel, Peat, and Gypsum.
  • Metamorphic Rocks: Originating from igneous or sedimentary rocks, they undergo changes due to pressure, heat, or water action. Examples include Gneiss, Marble, and Quartzite.

Types of Rocks and Their Metamorphic Forms

  1. Igneous Rocks:
    • Original Rock: Granite
    • Metamorphic Rock: Gneiss
  2. Igneous Rocks:
    • Original Rock: Basalt
    • Metamorphic Rock: Greenstone
  3. Sedimentary Rocks:
    • Original Rock: Limestone
    • Metamorphic Rock: Marble
  4. Sedimentary Rocks:
    • Original Rock: Coal (Organic)
    • Metamorphic Rock: Graphite, Coal
  5. Sedimentary Rocks:
    • Original Rock: Sandstone
    • Metamorphic Rock: Quartzite
  6. Sedimentary Rocks:
    • Original Rock: Shale/Clay
    • Metamorphic Rock: Slate, Mica, Schist


  • Weathering is the process by which rocks are chemically or physically disintegrated into fragments.


  • Any sudden disturbance below the Earth’s surface may produce vibrations or shaking in Earth’s crust, resulting in earthquakes.
  • The magnitude of an earthquake is measured by the Richter Scale.
  • The intensity of earthquake waves is recorded by a Seismograph.
  • The intensity of shaking is measured on the modified Mercalli Scale.
  • The focus is the point beneath the Earth where the earthquake originates.
  • The epicenter is the point just above the focus on the Earth’s surface.


  • Volcanism is the sudden eruption of hot magma (molten rock), gases, ash, and other material from inside the Earth to its surface.

Types of Volcanoes

  • Active: These volcanoes erupt frequently, examples include Mauna Loa (Hawaii), Etna (Sicily), Vesuvius (Italy), and Stromboli (Mediterranean Sea).
  • Dormant: Volcanoes that have not erupted for quite some time, such as Fujiyama (Japan), Krakatoa (Indonesia), and Barren Island (India).
  • Extinct: Volcanoes that have not erupted for several centuries, like Arthur’s Seat in Edinburgh, Scotland.
  • Ring of Fire: Refers to hundreds of active volcanoes found on the land near the edges of the Pacific Ocean.


  • A tsunami is a large ocean wave caused by sudden motion on the ocean floor, which could be an earthquake, volcanic eruption, or underwater landslide.


  • Earthquakes: Large underwater earthquakes cause the seafloor to move abruptly, displacing massive amounts of water and generating waves that radiate outward.
  • Landslides: Underwater landslides, triggered by earthquakes or volcanic activity, can also displace water and generate tsunamis.
  • Volcanic eruptions: Volcanic explosions and collapses can displace water and generate tsunamis, though less frequently than earthquakes.

Characteristics of tsunamis:

    • Long wavelength: Unlike wind-generated waves, tsunamis have a long wavelength, stretching for hundreds of kilometers in open water. This is why they may appear as only a slight swell initially.
    • Increase in height: When they reach shallow water near the coast, their energy becomes concentrated, causing the wave height to increase dramatically, sometimes reaching tens of meters.
    • Series of waves: A tsunami is not a single wave, but rather a series of waves that can arrive over minutes or even hours.
    • Destructive power: Tsunamis can cause major devastation due to their immense force and the large amount of water they carry inland.




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