There are three basic theories regarding the origin of life on earth. These however are hypothetical reasons and aspects laid down by eminent scientist who have been studying evolution for a long period of time. The first theory of origin of life from extraterrestrial sources was coined by Swedish scientist Svante Arrhenius. His hypothesis was developed during the 1990’s. The hypothesis laid down by Arrhenius suggested the idea of panspermia. The theory of panspermia suggest that life came from extraterrestrial sources. An analysis of a meteorite in 1996 revealed that the organic matter contained in it resembled the forms found on earth. Study had shown that the meteorite was from mars due to an asteroid collision. To support this theory further on, scientist from NASA had begun mars exploration. It was hypothesized that mars contained water bodies big enough to support life. It also reveals that life may have originated from Mars and then come (transported) to earth. But however exploration of Mars has not revealed any presence of life till date.
The second theory of evolution is that of origin of life from heterotrophs. Scientist believe that during the formation of planet earth, oceans, rivers and other sources contained organic molecules which could have possibly supported life of heterotrophs. Since there was no life initially, these compounds accumulated on the earth’s surface and there was abundant source for heterotrophs to survive. To support this theory, scientist use fossil records, since at that time there was no presence of oxygen and the only way for any species to survive was oxygen and heterotrophs survived in such climatic conditions. Study also reveals that heterotrophs have mutated from time to time to survive the climatic and atmospheric changes.
The third theory suggests that life originated from Autotrophs. The previous two theories may seem to be realistic but however the theory of autotrophic evolution is supported by many scientists. There is also evidence proving that life originated from autotrophs. Members belonging to Autotrophs are part of the domain Archaea which survive in extreme climatic conditions. Such type of environment was seen in historic times when life on earth was being formed. Present studies have revealed the presence of such organisms even today at hot springs like those found in Russia and Yellowstone Park. This live example of presence of such life forms reveal that only such species (autotrophs) could have survived in pre-historic times. These survive on inorganic raw materials present in such environments. Thus they must have survived back then and also today at present. Thus this study depicts a strong background suggesting the origin of life from autotrophs.
Thus there are three forms of theories suggesting that life originated from heterotrophs or autotrophs. And in an extremes study it also shows that life may have originated from extraterrestrial sources.
References
Davis WL, McKay CP. Origins of life: a comparison of theories and application to Mars. Origins of life and evolution of biospheres. 1996 Feb;26(1):61-73. Available at: http://www.ncbi.nlm.nih.gov/pubmed/8920171
