Q. What is Origin Of Life on Earth?Ans: The universe is very old - almost 13 billion years old. Huge clusters of galaxies comprise the universe. The Big Bang theory attempts to explain to us the origin of universe. It talks of a singular huge explosion unimaginable in physical terms.
The universe expanded and hence, the temperature came down. Hydrogen and Helium formed sometime later. The gases condensed under gravitation and formed the galaxies of the present day universe. In the solar system of the milky way galaxy, earth was supposed to have been formed about 5 billion years back.
There was no atmosphere on early earth. Methane,carbondioxide, and ammonia released from molten mass covered the surface.
The UV rays from the sun brokeup water into Hydrogen and Oxygen and the lighter H2 escaped. Oxygen combined with ammonia and methane to form water, CO2 and others.
The ozone layer was formed. As earth cooled, the water vapor fell as rain, to fill all the depressions and form oceans.
Life appeared 500 million years after the formation of earth, i.e., almost four billion years back. Some scientists believe that the life came from outerspace.
The first non-cellular forms of life could have originated 3 billion years back. They would have been giant molecules (RNA, Protein, Polysaccharides, etc.). These capsules reproduced their molecules perhaps.
The first cellular form of life did not possibly originate till about 2000 million years ago. These were probably single-cells. All life forms were in water environment only.
The version of a biogenesis, i.e., the first form of life arose slowly through evolutionary forces from non-living molecules is accepted by majority.
However, once formed, how the first cellular forms of life could have evolved into the complex biodiversity of today is the fascinating story that will be discussed below.