Theory of special creation-

This states that life was created by supernatural power in the form which has not undergone any changes. It was given by FATHER SUAREZ. God created life in six days from Materia prima and man was created on the sixth day. According to this theory, the earth is about 4000 years old.

Theory of catastrophism-

This was given by CUVIER, according to which after a gap of certain period called ‘age’ the world undergoes a catastrophe i.e. unexpected catastrophe which kills all the organisms and then God makes a new creation or new existence from inorganic matter.

Theory of Biogenesis-

This was proved by REDI, SPALLANZANI, and PASTEUR They disproved the theory of spontaneous generation i.e. Abiogenesis. Francesco Redi in 1668 evidenced that flies could not arise from rotten meat without their eggs. Spallanzani in 1767 confirmed that decomposition of meat is due to microbes in the air and it can be prevented by boiling and sealing the meat in sealed containers. Pasteur gave a concluding proof of life arising from pre-existing life using microbes and sterilization methods. He performed a “swan neck flask” experiment.

Cosmozoic theory –

Did life come from outer space? Some scientists believe that life came on earth from other stars or planets. They were the early Greek thinkers (Richter Helmholtz) who said that living organisms exist throughout the universe. Life was transferred from one planet to another in the form of some small units of life called spores or seed or sperms. The transfer of spores was termed Panspermia (suggested by Arrhenius in 1908). Panspermia states that life is present throughout the universe (pan complete). Transfer of life from one planet to another is called the Cosmozoic theory. Panspermia is still a favorite idea for some astronomers, but this theory has no specific proof.

Theory of spontaneous generation-

The supporters of this theory stated that life did not come from outer space. Rather there was a natural spontaneous generation of the living organism from nonliving matter present on the earth. They believed that the decayed and decomposing material like mud, straw, etc. could give rise to organisms like frogs, flies, etc. However, this perception was experimentally negated by many scientists. One of them was LOUIS PASTEUR. He by careful experimentation demonstrated that life comes only from earlier life. He presented that, in pre-sterilized flasks, life didn’t come from killed yeast while in another flask open to the air, new living organisms arose from killed yeast. This theory was dismissed once for all.

Theory of chemical evolution or Oparin- Haldane Hypothesis-

Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing nonliving organism molecules e.g. RNA, protein, etc. and that foundation of life was preceded by chemical evolution i.e. formation of diverse organic molecules from inorganic constituents.

Free atoms –> simple organic molecules and compounds –> First simple organic compounds –> simple organic compounds –> complex organic compounds –> First life.