Ever since man appeared on the earth, he developed the curiosity to know how life came into existence. Many philosophers, scientists and religious minds have put forth their views regarding this. The first one is the Theory of Special Creation which says “Everything was created by God or a supernatural power”. But science cannot prove or disprove the existence of God. The next theory put forth is the Panspermia Theory or better known as the Alien theory, supported by even Stephen Hawking, which tells that “Life originated in distant galaxies and arrived on the earth in meteorites.” Greek philosophers put forward the concept of Abiogenesis, which talks about spontaneous creation, around 600 BC. They believed “Vital Forces” like human sweat, morning dew and fruits, gave rise to life forms. But the most accepted theory of all is the theory of Biogenesis, which tells that life gives life, which was proved by great scientists like Spallanzani and Louis Pasteur. Louis Pasteur took some broth in a round bottomed swan shaped flask and boiled it so as to kill the micro organisms in the broth, and the Swan Neck to prevent the inflow of dust. The broth has still not deteriorated and is still present in Pasteur’s Institute in Paris. So Pasteur’s experiment highlights an intriguing question as to how the first form of life came into existence.The most widely accepted theory of formation of life is the Chemical Evolution of Life, by which, life originated from chemical substances over a period of time. The theory says-
'The Big Bang happened around 5 billion years ago resulting in a cloud of hot gases called nebulous which consisted of all the elements in gaseous form. As the earth started to cool, heavier metals formed the core of the earth and lighter metals formed the crust. As the earth gradually cooled, simple gases like Ammonia, Methane and water were formed. But the temperature of the crust was still very high. So as soon as the water cooled to liquid form and fell to the crust, it got vaporized and again went back into the atmosphere. This process of falling and vaporizing went on again and gain for millions of years, thus creating the ridges, furrows, mountains and water bodies.'
The atmosphere was reducing, i.e., no oxygen was present in the atmosphere. The simple gases combined together with the help of energy from lightning and geothermal heat to form simple sugars, fatty acids and amino acids. As these organic compounds are Hydrophobic, they were present in water as colloids, which was called a Primitive Soup. These combined to give polypeptides, polysaccharides, nitrogen bases, nucleotides and phosphates, which are the basic building blocks of DNA or Deoxyribonucleic acid. These DNA molecules gave rise to the first form of life. These DNA molecules self replicated and synthesized proteins. This resulted in the first form of life, which were heterotrophs.
Gradually, due to mutation, which depends only on chance factor, autotrophs were formed. They started fermenting the oxygen dissolved in the ocean and transformed the atmosphere from 0.00% Oxygen to what we currently have, 21% Oxygen, without which we cannot live. This was how the first form of life originated.
By: Chirag RS. (Writer at Science Panorama)