by George Efstathiou

Created on: December 20, 2006   Last Updated: May 02, 2007

The origin of life is a mystery, hard to be solved. There are three major theories:
1. Creation (All major religions believe that God created life),
2. Extraterrestrial origin (There is evidence showing that life could have been transferred to earth with meteorites)
3. Spontaneous origin (Accepted by most scientists)

Let's summarize the theory of spontaneous life's origin. It is accepted that it happened during a period 3-4 billions of years ago. During that time, the atmosphere had nothing to do with the atmosphere we know. There was no oxygen. Instead it consisted mostly of methane, ammonia, water (gas) and carbon dioxide. Freezing of the planet led to the creation of oceans. At first, simple organic molecules were created by simple inorganic molecules (CH4, NH3, H2 and H2O) as a consequence of heat, radiation and thunderstorms. Acetone, formaldehyde and HCN reacted with other organic molecules to form amino acids and nucleotides including ATP (molecule important for many biological reactions). It is believed that these molecules were accumulated in the ocean. This led to the formation of polymers (proteins, DNA molecules and lipids). Argil surfaces could have contributed to the catalysis of the necessary reactions. Lipids were formed together to create vesicles which contained RNA (some of which could act as ribozymes). Those vesicles had the ability to absorb, metabolize and discard molecules, and most importantly, the ability to divide. Some of those, by natural selection, evolved to archeae, ancestors of bacteria.

Archeae and bacteria should have had photosynthetic ability, which helped them survive, and led to enrichment of the atmosphere with oxygen. Evolution of these simple forms of life to more complicated single-celled organisms, with the aid of natural selection, resulted in the production of a large number of different organisms. Some of those could survive only in multi-celled formations. Species were created during periods of million years. At some point the ancestors of plants and animals appeared, which gave birth to all the species as we know them today and many others that were vanished.

All these are hard to get, because we are thinking in terms of years or decades, and also, we don't have a clear image of nature as a whole. Those processes required millions of years to take place, under environmental conditions which we cannot imagine and in great amounts of organic matter. Billions of tons of matter must have been accumulated in order for a

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