Theories of Origin of Life:
Various theories have been put forward to explain the origin of life.
1. Theory of Special Creation:
According to this theory, each and every life form was created by supernatural power as a separate and fixed entity without changing itself all of a sudden.
2. Theory of Spontaneous Generation:
This theory states that various types of living organisms originated spontaneously from non-living substances automatically in course of time. Anaximander (611-547 BC) and Aristotle (384-322 BC) were the main propounders of this theory.
3. Theory of Cosmic Origin:
This theory was proposed by Ritcher (1865). According to this theory, protoplasm reached the earth in the form of spores or germs from some unknown part of the universe with the cosmic dust and subsequently evolved into various forms of life.
4. Theory of Oparin and Haldane in Favour of Origin of life:
In 1920, Alexander I. Oparin suggested that under the influence of solar radiation, thunderstorm, volcanic eruptions, heat due to radiation, UV radiation, cosmic rays, etc. The gaseous elements in the primitive environment of the earth react to produce small organic molecules. Simple small organic molecules on polymerization 1928 proposed a similar idea on the origin of living forms.