Modern Theory
Naturalistic theory: According to this theory Life originated upon our earth spontaneously from nonliving matter. But there are two significant points in this regard to be carefully noted:
(A) Firstly: life originated upon the earth, not by a sudden chance or random mixing of non living matter, but as a result of a long, series o physical chemical changed which brought about a gradual evolution of, first inorganic and, then, organic compounds in according ever changing environmental conditions. This is called Chemical Evolution. It culminated into the synthesis of Protoplasm or Life Substance as the most complex crystsllo colloid mixture of Nature.
(B)Secondly: a chemical evolution of matter as envisaged above cannot occur under the present Environmental conditions upon earth; conditions suitable for it existed only upon primitive earth.