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.
- 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.
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.
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.
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
- 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