Origin of life on earth
Scientists have debated the origin of life on planet earth, and there are competing theories for this. To further explain origin of life, scientists have done experiments to prove their theories, but there is no single theory that is acceptable to all. Nonetheless, all the theories agree that it is though propagation that living things continue live on planet earth. Even though, scientific theories are fairly recent there were hypotheses explaining life’s origin from ancient philosophers. Additionally, scientists posit that all living organisms had a common ancestor, as represented by shared characteristics among living things distributed among the various living kingdoms. This paper will look into three theories on origin of life, the extraterrestrial explanation, and origin as heterotrophs and as autotrophs.
The theory of extraterrestrial origin of life states that life could probably have started outside planet earth, whereby spores or seeds from outer space were deposited on earth. The are various explanations to this phenomenon, with some scientists also stating that life was always there on planet earth, and hence there is no need to look for explanations on origin of life. Nonetheless, movement of spores from different planetary spaces to earth offers the most plausible explanation for the extraterrestrial origin of life (Enger et al., 2007). The various explanations for movement of spores are not in agreement, there are various mechanisms through which this takes place and this could have been from meteorites, comets or other heavenly bodies, from which the spores came into earth from outer space.
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The heterotroph hypothesis posits that life started from simple life forms when there was a primitive earth and these primitive life forms lived in the oceans. To further give credence to this hypothesis, supporters say that evidence collected from oceans suggest that the ocean still contains primitive cells (Enger et al., 2007). Furthermore, these organism can be found in fossils where there is little oxygen, suggesting that they were anaerobic leading to more carbon dioxide release. Nonetheless, these organisms increased over time, and it was no longer possible to consume organic molecules as energy sources, because this prove unsustainable after increased demand and limited supply of the organic molecules. Additionally, some of the heterotrophs mutated enabling them to change previously unusable matter into usable through complex biochemical process (Enger et al., 2007).
An alternative explanation on life on earth is the autotroph hypothesis, and this hypothesis arose out of scientific evidence and discoveries after the heterotroph hypothesis had been the main theory for long. Supporters of this theory say that autotrophs live in harsh places, which have similarities with the earth. To give credibility to this theory is the discovery of such organisms in harsh places including hot springs and in deep ocean floors (Enger et al., 2007). The discovered organisms depend on energy released through inorganic chemical processes, and hence if the earliest organisms had similar features then autotrophs were the first to appear on earth (Enger et al., 2007). Scientists have long discovered that the earth was once hotter than modern earth, and it is plausible that such organisms would have thrived in such conditions. Scientists also propose that appearance of autotrophs would possibly lead to competition with heterotrophs, and combined with mutation over time this led to adaptation and division of such organisms into Domains Eubacteria and Archaea (Enger, 2007).