Origin of Universe
The most accepted theory of the origin of life on earth is the Big Bang theory.
Big Bang Theory
This theory was proposed by Abbe Lemaitre in 1931. According to this theory, 15 billion years ago cosmic matter was in condensed form.
This condensed mass consisted of neutrons, protons, and electron-like particles. Suddenly, this condensed mass exploded, and its fragments (cosmic materials or nebulae) got scattered into space at an enormous velocity making a “big bang” sound and thus the theory is known as the big bang theory. From the exploded fragments (cosmic materials or nebulae) the solar system was formed.
Formation of the Solar System and Earth
The nebular hypothesis explains the origin of the solar system. It was first proposed by Kant in 1755. After the explosion, solar nebulae gradually cooled and contracted to form a cold cloudy mass of cosmic dust and gases. As the universe expanded, the temperature decreased, and various galaxies were formed. For example-Milky Way galaxy. This galaxy consists of a solar system, in which the earth is present. Earth is one of the planets of the solar system and originated about 4.6 billion years ago. When the earth was formed there was a rotating cloud of hot gases and cosmic dust called a Nebula. There was no atmosphere on earth. The UV rays split water into Hydrogen and Oxygen and the lighter H2 escaped. Water vapor, methane, carbon dioxide, and ammonia released from molten mass covered the surface. Oxygen reacts with ammonia and methane to form water, CO2, and others. Water vapor formed the rain and water fell down and filled all the depressions and formed oceans. First life emerged 500 million years after the formation of the earth, i.e., almost four billion years ago.
Origin of Life
The origin of life on earth is one of the mysteries to mankind. According to a common man, life is gifted by god whereas scientists believe that life has originated from non-living matter by natural means. This mystery of whether life originated from non-living matter was solved by scientists Pirie. It has been proved that the first non-cellular forms originated 3 billion years back from RNA, Protein, Polysaccharides, etc. The first cellular form of life was single cells that did not possibly originate till about 2000 million years ago. All life forms were present in the water only.
Also Read: RNA