The Earth


Earth consists of 71% of water and 29% land. This 29% landmass is further divided into 7 continents.

  1. Asia
  2. Africa
  3. Europe
  4. North America
  5. South America
  6. Antarctica
  7. Australia

Water Bodies on earth.

Water 71%
97.5 Ocean and Seawater
2.5% Fresh Water

Water bodies are –
• the Atlantic Ocean
• the Arctic Ocean
• the Indian Ocean
• the Pacific Ocean
• the Atlantic Ocean

Earth’s Profile  

Age4.550 billion years (Uranium Dating)
Mass5.976 x 1024 kg 
Volume1083 x 1012 km3 
Mean Density5.513 g/cm3 
Total Land Surface510 million sq km 
Land Area29.2%
Water area70.8%
Equatorial Circumference 40,075 km
Polar Circumference40,024 km
The shape of the earthAn oblate spheroid, or Spherical irregular shape or Geoid Shape.
Average Distance from the moon3,82,500 km
Tilted23 ½
Rotation Speed23hr, 56 min, and 4 sec  (West to East)
Revolution Speed365 Days, 5hr, and 45 Sec.
Day and Night Equal21st March (Vernal Equinox) 23rd September (Autumnal Equinox))
Longest Day21st June (Summer Solstice) Sun is vertically overhead at the Tropic of Cancer Shortest night 
Shortest Day22nd December (Winter Solstice) Sun is vertically overhead at Tropic of Capricorn Escape velocity 11.2 km/sec 
The surface temperature of Earth16 – 18 degree celsius

Earth Equator diameter – 12,756
Earth’s Polar diameter – 12,714
Difference between Equator and polar dimeter is 42 Km.

The shape of the Earth: Geoid Shape

The Earth is an oblate spheroid. It is almost spherical, flattened a little at the poles with a slight bulge at the center (equator).
The geoid is defined as the oceanic surface which approximates the mean sea level. It is perpendicular to the direction of the force of gravity.
Since the mass of the Earth is not uniform at all points, the magnitude of gravity varies, and the shape of the geoid is irregular.

Earth’s Layers

The Earth’s interior is composed of three major layers: the crust, the mantle, the Core.
The Crust – SIAL (Silicon-Aluminium) Upper part of the earth. (35 km)
The Mantle – SIMA (Silicon-Magnesium) Lower part of the crust. (2900 km)
• Mantle’s lower part is known as the Asthenosphere.
The Core – NIFE (Nickel-Iron) innermost part of the earth. 3500 km.
Eduard Suess has explained in (the 19th Century) the interior of Earth on the basis of chemical composition as SIAL, SIMA, and NIFE.

Earth’s atmosphere

Earth’s atmosphere is like a blanket of protection.
Survival on earth totally depends on the atmosphere.

Air present in the atmosphere by Percentage.

Nitrogen (N2)78.08
Oxygen (O2)20.95
Argon (Ar)0.93
Carbon dioxide (CO2)0.036
Neon (Ne) 0.002
Helium (He)0.0005
Krypto (Kr) 0.001
Xenon (Xe) 0.00009
Hydrogen (H)0.00005

Earth’s Atmosphere layer

Troposphere (About 30 km) The air we breathe exists here.
All the weather phenomena like rainfall, fog and hailstorm occur in
this layer.
Stratosphere (50 km)
(Ozone layer) This layer is almost free from clouds.
Ideal for flying airplanes.
It contains a layer of ozone gas.
Mesosphere (up to 80 km) Meteorites burn up in this layer on entering from the space.
Thermosphere (80 to 400 km) Radio wave transmission
Exosphere (uppermost part) This layer has very thin air.
Gases like Helium and Hydrogen float into space from here.

• Perihelion Nearest position of the Earth to the Sun about 147 million km away. (Jan 3)
• Aphelion Farthest position of the Earth from Sun about 152 million km away. (July 4)


Imaginary lines are drawn on the Earth’s Surface parallel to the equator. The Equator (0°) is the biggest latitude that divides Earth in two equal hemispheres (North and South).

Tropic of Cancer – 23.5° N
Tropic of Capricorn – 23.5° S
Artic Circle – 66.5° N
Antarctic Circle – 66.5° S
There are total 181 latitudes including equator.
Each degree of latitude equal 111 km

Longitudes (Meridians)

• Meridians are a series of semicircles that run from pole to pole passing through the equator.
• Prime Meridian passes through Greenwich near London, divides the Earth in the Eastern and Western hemispheres. Its value is 0°.
• There is total 360 meridians of longitude on earth.
• This line passes through Royal observatory at Greenwich near London.
• Longitude has very important function i.e., it determines local time in relation to Greenwich Mean Time (GMT).
• 1° change of longitude corresponds to 4 minutes difference in time.


Springs – 21st

  • March the sun is directly overhead the equator.
  • This is the season of spring in the northern hemisphere.
  • Vernal Equinox – on this date day and nights are equal.    

Summer – 21st

  • June the sun is directly overhead the tropic of cancer, thus the northern hemisphere experiences summer.
  • Summer Solstice – where the Longest day.   

Autumn – 23rd September

  • The sun returns to the equator and the northern hemisphere experience autumn.
  • Autumnal Equinox – on this date day and nights are equal.    

Winter – 22nd December

  • The sun is at the tropic of Capricorn, and the northern hemisphere experience winter.  
  • Winter Solstice – where the longest night.


  • Regular rise and fall of the sea water between the interval of 12 hours and 26 minutes.
  • Both Sun and Moon exert gravitational force on earth is resulting the tide.
  • Moon has a greater control over the tide because moon is closes to the earth. (2.17 times more control than SUN) 

Spring tide

  • When the Sun, Moon, and Earth are in a straight line (syzygy), at this position gravitational force is greater because force is exerting by both Sun and Moon.

Neap Tide

  • Lowest Magnitude tide, force of Sun and Moon act opposite each other.
  • This happens only on first and third quarter.

Geostationary Orbit Height – The geostationary orbit of the earth is at a distance of about 36000 km from the earth’s surface.

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