best ias books

Origin of Earth

Gaseous Theory (1755)

  • By Imanuel Kant (German)
  • Primordial matter was evenly distributed in shape of small & cold particles from which our earth & other planets of solar system formed

 

Nebular Hypothesis (1796)

  • By Laplace (French)
  • Primordial matter existed in form of intensely hot & rotating gaseous mass (Nebula), Which cooled with time
  • This resulted in decrease of its volume & increase in its rotational speed, which in turn increased its centrifugal force
  • The centrifugal force when exceeded gravitational force, a ring shape deformed from nebula & many other rings formed out of its breaking.
  • These rings on cooling became planets & satellites & remaining part of nebula is sun

 

Planesimal Hypothesis (1900)

  • By Chamberlain & Moulton
  • A wandering star approached the sun & exerted its gravitational pull on the sun, which resulted in separation of cigar shaped material from the sun.
  • As star moved away from the sun, material separated from the sun started revolving around the sun & condensed into planets at later stage.

 

Tidal Hypothesis

  • By Sir James Jeans (British) & Harold Jeffrey
  • Sun was a gaseous mass; another star several times larger than sun accidentally came close to it & pulled gaseous mass away from the sun due to its gravitational pull.
  • Giant tongue of matter came out from the sun & planets were formed

 

Big Bang Theory (1929)

  • By Edwin Hubble (American)
  • Everything in the world emerged from a point known as singularity (of indefinite mass & indefinite density) about 13.7 billion years ago.
  • As galaxies moved away, space between them expanded (Red shift).
  • As the universe expanded, hot radiation in original firewall cooled down, which led to formation of different galaxies which further broke into stars & finally stars broke to form planets.

Origin of Earth big-bang-timeline


Curved Surface of Earth (Spherical form)

Ship’s visibility When a ship appears over the distant horizon, top of the mast is seen before the hull & vice a versa.

Spherical earth prove

Sunrise & Sunset Sun rises & sets at different times in different places. As earth rotates from west to east, places in east see sun earlier than those in the west.

Sunrise & Sunset

Lunar eclipse Shadow cast by earth on the moon during the lunar eclipse is always circular

Driving poles on level ground on curved earth
  • Engineers while driving poles of equal length at regular intervals on the ground have found that they do not give a perfect horizontal level.
  • Centre pole normally projects slightly above the poles at either end because of curvature of the Earth
  • Hence they have to make certain corrections for this inevitable curvature i.e. 8” to a mile

 

Aerial Photographs
  • Pictures taken from high altitudes by rockets & satellites show clearly the curved edge of the earth.
  • This is perhaps the most convincing & up to date proof of earth’s sphericity
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