Megha Parmar

How life originated on the Earth?

Earth, the only planet detected where life throbs. Travelling back to 4.5 billion years ago the earth was entirely rocky. There was no trace of life. After 1 billion years that is 3.5 billion years ago from the present, the first form of life prevailed which was photosynthetic cyanobacteria.

There are many theories on how the first form of life came into existence. Let's discuss one by one.

Theory of Special Creation:

According to religious mythology, life is created by Almighty. However, there is no experimental proof to this theory but it is still strongly believed.

Theory of Cosmic Origin:

According to some researchers and philosophers, life originated in several parts of the galaxy in the universe. There was dispersion of spores which consisted of protoplasm (all raw materials required for life to originate) in the entire universe. In some parts, these spores succeeded in developing and the earth was one of them. Arrhenius called these spores Panspermia.

Theory of Spontaneous Generation:

This theory states that life originated from inanimate matter like decaying straw, mud, rocks etc. According to the Greek philosopher Thales, Anaximander, Plato and Aristotle mud of the river Nile gave rise to frogs, lizards and crocodiles.

Theory of Biogenesis:

Francesco Redi, Spallanzani and Louis Pasteur conducted an experiment in which they took two flasks having killed yeast, one was pre-sterilized and disconnected from the atmosphere. On the other hand, the second flask was kept in the open air.

The pre-sterilized flask could not generate life whereas flask kept in contact with air generated new microorganisms. This theory completely proved the Theory of Spontaneous Generation false.

Theory of Chemical Origin of Life- most widely accepted by scientists:

According to this theory, life originated when inorganic molecules were converted into organic molecules by chemical reactions.

Early earth's atmosphere had reducing nature due to hydrogen and very high temperature. Compounds like CH4, NH3, CO2, H2O, H2 were present. Due to lightning and volcanic eruptions energy was provided to these compounds to react and form organic molecules like amino acids, sugars, N2 bases etc. These organic compounds formed proteins, lipids and nucleic acids.

There was formation of the ozone layer and reduction in temperature took place. This led to the appearance of water bodies due to raining. The atmosphere became oxidising in nature.

The first life originated in the water body from coacervates. Coacervates are distinct bodies which have protein, lipids, nucleic acids.

Oparin and Haldane conveyed this theory. It was proved by Urey- Miller by conducting an experiment in the lab. They created the same reducing atmosphere of the earth and provided lightning by electric sparks. Later they found organic molecules in the water.