Whence came life on the surface of the earth? Whether or not a complete answer to this question may be found within the context, and content, of modern science, may be a moot question. It is our purpose to see how far we can devise an answer, and how satisfactory it may be, within that context. We trace a path from the primitive molecules of the primeval earth's atmosphere condensed from space through the random formation of more or less complex organic molecules, using the available energy sources of ultraviolet light, ionizing radiation or atmospheric electrical discharge, through the selective formation of complex organic molecules via autocatalysis, finally, to the informatiion-transmitting molecule which is capable of self-reproduction and variation. In addition, somewhere, either during the course of this Chemical Evolution, or perhaps succeeding it, a system has been evolved in which the concentration of the reaction materials was retained in a relatively small volume of space, leading to the formation of cellular structures. Man is about to send back into space some bits of the dust from whence it originally came, It is thus not only timely but more significant than ever before to ask again the question: What aremore » the probabilities that cellular life as we know it may exist at other sites in the universe than the surface of the earth?« less