World Geography for UPSC: Earth and Solar system


World Geography for UPSC:

Geography a subject which helps aspirants in scoring good marks in competitive exams. Geography in exams is of very simple nature but questions asked are tricky and confusing.

Geography on the whole covers Indian Geography and World Geography covering mapping and other basic parts of physical geography.

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We at LST committed to our motto have designed world geography for UPSC well researched and scientifically designed article for preparation.

Note-  Article presented here is designed for UPSC SSC and Other competitive exams.

Origins of Earth

Came into existence 4.6 billion years back


Gaseous Hypothesis: (Kant) Clouds of gases flattened down under gravity to create earth.

Nebular Hypothesis: (Laplace) Formed by solidification of a ring thrown away by a rotating nebula (sun)

Tidal Hypothsis: (Jeans and Jeffreys) Proposed effects of two nebulas in forming the earth. A larger nebula came close to the smaller one (sun). The gravitational pull caused tidal upsurge on the surface of sun. As the larger nebula moved away, small rings of nebula separated from the smaller nebula and formed the earth and other planets.

Nature of earth:


Layered structure: Crust, mantle, core

Crust: sial (silica and aluminium)

Mantle: sima (silica and magnesium)

Outer Core: (nickel and iron)

Core: Iron

Time line:

  • Age estimated through carbon-dating
  • Three Eras: Palaeozoic (542 to 241 million years ago), Mesozoic (240 to 64 million years ago) and Cenozoic Era (63 million to 10000 years ago). The era before the Palaeozoic era is called the Pre-cambrian period.
  • Earlier forms of life have existed as long ago as 3.5 billion years back. Human species came into existence around 2 million years back.

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Solar System

Sun and eight planets

All planets rotate on their axis from west to east except Venus and Uranus which rotate from East to West. Direction of revolution around the sun is also west to east.

Jupiter has the largest number of satellites (63) while Mercury and Venus have none.

Asteroids and planetoids: Bodies revolving around the sun that are small to be classified as planets. Asteroid belt between the orbits of Mars and Jupiter. Jupiter Trojans are asteroids revolving around the sun in Jupiter’s orbit.

Near-earth objects: perihelion distance <1.3 AU.

Geocentric View: Ptolemy; Heliocentric View: Copernicus

Inner planets: Mercury, Venus, Earth and Mars. Rest are outer planets.

Mercury and Venus which are closer to the sun that earth are called inferior planets. Venus is the closest planet to earth.

Brightest: Venus

Smallest: Mercury

Most elliptical orbit: Pluto. It intersects with Neptune’s orbit.

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Earth: Shape and Size

Shape: Spheroid. (Oblate spheroid or oblate ellipsoid)

Diameter: Equatorial – 12757 km (7927 miles); Polar – 12715 km (7901 miles)

Geoid: Imaginary shape of the earth where sea level surface of the oceans is extended to the continents to form continuous figure.

Mass: 5.976*1024 kg

Volume: 1.083*1024 liters

Mean density: 5.518 kg/litre

Total Surface Area: 509.7 million Land – 148.4 million (29 pc). Water – 361.3 million sq. Km (71 pc)

Rotation: 23hrs 56 mins 4.09 sec

Revolution: 365 days, 6 hrs, 9 mins and 9.54 sec

Highest point: Mt Everest (8848 m asl)

Lowest point on land: Coast of Dead sea (399 m bsl)

Mean height of land: 756 m

Deepest point: Mariana trench (near Guam: 11033 m bsl)

Avg ocean depth: 3730 m

Earth’s Crust: Oxygen (46.6 pc), silicon (27.7 pc), Al (8.1 pc), Iron (5 pc), Ca (3.6 pc), Na (2.8 pc), K (2.6 pc), Mg ( 2 pc). Other elements (1.6 pc)

Hottest: Lut deserst, Iran (70.7 degreeC)(internet). Al Aiziyah, Libya (58 degree C)

Coldest: Vostok Station, Antarctica (-89.6 degree C)

Inclination on polar axis: 23 deg 26 min 50 sec

Orbital Speed: 29.8 km/s

Mean distance from sun: 149,598,500 km ( 1 AU).

Max distance: 152 million km (aphelion, July 2-5)

Min distance: 147 million km (perihelion, Jan 2-5)


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