Theories explaining the Origin of Life

Curiosity often prevails on young minds, pondering over the question: How life originated on earth? The story traces back to a time almost 4 to 6 billion years ago, when earth originated from the condensation of cosmic clouds. The most well-known theory on the origin of life on earth, as proposed by Oparin and Haldane, can be explained on the basis of Biogeny, Chemogeny and Cognogeny as follows.

The earth at that time was a sphere of hot gases, at about 5000C, with everything on it in the molten state. The heavier elements like Nickel, Iron and radioactive elements formed the molten core, while other lighter elements like Magnesium, Silica and Aluminum formed the mantle and the crust. The lightest elements like nitrogen, oxygen, hydrogen and carbon formed the primitive atmosphere.

As the Earth started to cool down gradually, these upper layer elements reacted with one another to form methane, ammonia and water. The superheated steam got condensed into water droplets, and boiling water started flooding the surface of the earth, thereby starting the first water cycle on earth. The hot boiling broth that was formed came to be known as the 'Haldane soup' or 'primordial soup'. This Primetime Ocean was alkaline in nature, and supported the synthesis of organic compounds. Even the penetration of ultraviolet radiations through the upper atmospheres, the electrical energy from lightning and the heat energy from volcanic eruptions all favored the formation of such organic molecules. The atmosphere that prevailed then was a reducing one; rich in water vapor, methane and hydrogen, while lacking oxygen.

Ammonia, methane and water which were formed earlier, reacted spontaneously to form different organic micro molecules, such as amino acids, fatty acids, glycerol, nucleotides, and monosaccharaides. These micro molecules were then polymerized in order to form macromolecules like nucleic acids, lipids, proteins and carbohydrates. These macromolecules in turn formed colloidal aggregates, which came to be referred as 'coacervates' in the aqueous medium. These coacervates were not only able to absorb and assimilate more organic compounds from the environment, but they also grew membranes around themselves, to be prevented from being dilute or destroyed. Ultimately, these colloidal aggregates or rather organelles, absorbed chemicals, grew and divided and obtained even more energy by absorbing more organic compounds around them.

Thus these organelles together, formed the first structural and functional unit of life; the cell. All these explanations were based on probabilities of all the above mentioned conditions having occurred together.