Scientists and their theories about the origin of life:

*Theory of special creation: According to it life has been originated from supernatural powers of god.

*Theory of panspermia: According to it, life has been originated from spores.

*Theory of spontaneous generations: According to it , life has been originated from dead and decaying matter .

*Theory and experimental proof given by Louis Pasteur:

Theory: According to him, life has been originated from pre-existing life.

Experiment: He placed killed yeast in pre-sterlised flask and another flask open in air. He observed that life did not originate in the pre-sterlised flask but new living organisms appeared in the opened flask.

*Theory of chemical evolution (Operin and Heldane theory): According to it , life has been originated from pre-existing non-living organic materials.

Experimental evidence of chemical evolution (Millers experiment):

The conditions on earth favouring chemical evolution were high temperature, volcanic storms, reducing atmosphere containing, CH4, NH3, etc.

1)Miller,created electric discharge in a closed flask containing CH4, H2, NH3  and water vapour at 8000C. He observed formation of amino acids.

2) In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats. Analysis of meteorite content also revealed similar compounds indicating that similar processes are occurring elsewhere in space.