History Of Earth

Earth and Space

Figure: Earth

Earth is an only living planet known up this time. It lies in solar system as inner planets. with it Mercury, Venus and Mars are also included. Jupiter, Saturn, Uranus and Neptune are outer planets. Sun lies in the center of solar system and all other planets revolve around the sun in elliptical orbit. Solar system was formed billion years ago.  It has been always curiosity for man to know about the origin of the earth and entire solar system. On the other hand, our universe is very vast. All the matter, energy and space together make our universe. It consists of galaxies, stars, planets, comets, meteors, asteroids, and so on.

It is curious to know that the formation of universe and our solar system. Numerous questions about the formation of Himalayas, Mountains, rivers, vegetation, oceans, etc. on earth is another curiosity. |Many scientists have tried to to explain about the origin of the Universe and solar system including our earth. But there is no universally accepted theory about the origin of the earth.

Some Hypothesis about the origin of the earth

Some scientists believe that our earth was formed from a big star. Other group of scientists believes that earth was evolved from the gases and dust particles. Some of them believe that it was formed from the repulsion of the two stars. We don't have universally accepted theory about the origin of the earth. Some hypothesis put forward some of scientists have been explained below;

Old Planetesimal Hypothesis

This Hypothesis was put forward by a French scientist George Wofan in 1749 A.D. This hypothesis explains that our earth with other planets was evolved from a collision of comet with sun. A large mass of gaseous was thrown into the space into space from the sun. This mass was cooled to form the planets and satellite of the solar system.  The remaining mass of the sun remained sun.

Nebular Hypothesis

            This hypothesis was first proposed by Immanuel Kant in 1755. He proposed that gaseous clouds, nebulae, slowly rotate, gradually collapse and flatten due to gravity forming stars and planets. A similar model was developed independently and proposed in 1796 by Pierre-Simon Laplace. He believed that Sun originally was formed from the contraction of hot mass of gases in whirlpool motion. On the other hand an extended hot atmosphere of gases and dust covered throughout the volume of the solar system. This theory futures a contracting and cooling of solar cloud called the proto solar nebula. As this cooled and contracted, it flattened and spun more rapidly. In this process a series of gaseous ring of material, the planets were formed from the condensation of the material. Laplacian model was similar to Kant’s model.

Tidal Hypothesis

       An attempt was made by James Jeans Harold Jaffrey in 1917 A.D about the formation of the solar system. According to him the planets were considered to have been formed due to the approach of some other star to the Sun. The big star drew the large amount of matter of the sun by their mutual tidal forces. These bulged mass could have them condensed into planets. Solar system from milky way galaxies. All the planets including sun have been from the dust and the gases particles left in the galaxies called nebula. The planets began as dust grains in orbit around the central newly formed star from the accumulation of gases. Through direct contact, these small grains formed into clumps up to 200 meter in diameter, which in turn collided to form larger bodies. These gradually increase through further collisions and take the shape of planets.

Reasons for Origin of the Organisms On Earth

           The estimate age of the earth is 4.5 billions years. When earth was formed the temperature, pressure and environmental conditions were not appropriate for the life. Billions of years were taken by the earth for stabilization and maintenance of appropriate climate. Earth from the gases state changes into molten state and slowly solidified. Later atmosphere was formed. From the combination of Hydrogen and Oxygen rainfall occurred. After the formation of water, first simple form of life was formed in water. Life on earth molded from simplicity to complicity. This means simple organisms were developed first and advanced were formed were after  millions of years. The major reasons for evolution of organisms on earth are as follows:

a.   Presence of atmosphere over the surface of the earth. Oxygen, Nitrogen and Carbon dioxide are the gases needed for the existence of life.

b.  Presence of Ozone layer in the atmosphere.

c.   Presence of water in different bodies. Three part of the earth surface is covered with water. On other hand 3% oxygen is dissolved in water.

d.  Average temperature of the earth is suitable for the organisms to the survive.

e.   Climatic conditions and environment for the entire organism are suitable to that they can adapt themselves.

f.    The distance between earth and sun is suitable for the life to mold on earth.

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