Oparin- bathed in sunlight, combined together to create

 Oparin- Haldane theory and early ideas about origin of life.The hypothesis that the early Earth was composed of all necessary ingredients to create life has been supported by several prominent scientist including Charles Darwin. In 1871, Darwin wondered if life began in a “warm little pond”, where simple organic compounds bathed in sunlight, combined together to create a life-like substance such as protein. Darwin suggests that life was created in aquatic environments on primitive Earth where the temperatures where high and high concentration of biological building blocks could have existed. Darwin’s idea gave inspiration to future scientists to create the first hypothesis of how life began.In early decades of 19th century, the Soviet biochemist Alexander Oparin (1924) and the English biologist John Haldane (1929) independently suggested that in the primitive atmosphere with the absence of oxygen and thus an excess of negative charge that could cause reducing reactions by adding electrons to compounds. If there was enough supply of energy through ultraviolet (UV) light or lightening, then chemical reactions between the existing carbon dioxide, methane, ammonia and hydrogen could have led to the creation of huge diversity of host organic compounds within the early aquatic environment.    In 1953, in order to test the Oparin-Haldane theory, the American chemist Stanley Miller simulated electrical discharges in conditions that he thought that resembled the early atmosphere. Miller connected glass flasks and circulated four chemicals. On boiling water, he circulated warm vapour in an atmosphere of simple organic molecules including methane, ammonia and hydrogen gas. After, he subjected the chemicals to repeated electric shocks by passing an electric spark. Finally through a cooling jacket that condensed the vapour and directed back into the boiling flask. After a week, Miller noticed a change on the colour of the water suggesting the formation of new chemicals. By using chromatography, Miller identified the creation of three different amino acids including glycine, ?-alanine, and ?-alanine. Miller concluded that if lighting on early Earth could have played the same role as the spark in his experiment then the ocean of early Earth would have been rich in biological building blocks. However, today it is believed that the early atmosphere may have been dominated by carbon dioxide and nitrogen rather than methane and ammonia. Some scientists argue that in these neutral gas mixtures, the organic compound synthesis is much lower whereas others think that by using naturally occurring chemical compounds such as ferrous iron can inhibit oxidation process of synthesized organic compounds by nitrates and nitrites, it is still possible to generate amino acids (Cleaves et al. 2008).RNA worldThe RNA world appeared to be influential for several scientists, creating a long lasting picture of the primordial Earth. The discovery of ribozymes in 1980, enabled scientists to believe that the RNA world is plausible. In 2009, John Sutherlard and his colleagues managed to activate pyrimidine ribonucleotides under environmental conditions of early Earth scenarios. Even though, the precise consistence in early Earth’s chemical is unknown, the group of scientists provided strong evidence of the RNA world by creating the model that has the potential to be elongated and replicated. However, the phosphate group is yet to be added.Panspermia hypothesisPanspermia hypothesis suggests that life may have initially originated in a different planet and arrived on Earth perhaps on a meteorite (lithopanspermia). The idea was originally introduced by the German physicist Herman E. Richter in 1865. The second aspect of the same theory was introduced by Arrhenius in 1908 and supports that life arrived on Earth travelling through the space by the radiation pressure of light. Lastly, the third scenario under panspermia hypothesis supports the idea that intelligent creatures from a different planet might have sent life on earth.Panspermia hypothesis has been supported by many prominent scientists and even today some researchers have shifted their interest into different planets to find answers concerning how life started on Earth. Some complex molecules have been found in the large meteor that formed the Sadbury crater in Canada, 1.85 billion years ago and organic molecules such as carbon, hydrogen oxygen, sulphur, phosphorus and nitrogen that can act as precursors for the biosynthesis of amino acids have been found in comets and interstellar space. In 1996, McKay et al. studying a Martian meteorite (H 84001) claimed to have found objects resembling fossils of bacteria, or biological processes that produced by the minerals and chemicals. However, the study has been criticized by several scientists due to the lack of evidence. (Anders et al.; Kerr 1997a; and Weiss etc al. 2004)Has the origin of life happened just once?All life forms on Earth share a common ancestor, known as the last universal common ancestor (LUCA). Despite the morphological differences, every living thing today shares fundamental characteristics. In particular, the basis of the mechanisms that the genetic information is transmitted and expressed remains unchanged through the different forms of life. For instance, the way that the information is transmitted through the triplet code and the translation into proteins. Some sophisticated modifications that correspond to organisms with higher complexity suggests that Eukaryotes derived from Prokaryotes. Thus, the life as we know it at present has originated only once when these mechanisms became established.Further evidence of the single event of genesis can be the specific form in dissymmetry of biological molecules. In all living organisms, all amino acids are laevo-rotary (to the left) whereas in all nucleic acids, the sugars are dextro-rotary (to the right) form. The certain dissymmetry of biological molecules suggests that life originated only once as under laboratory conditions the specific biological molecules can function with the same efficiency when their dissymmetry alters (i.e. amino acids being dextro-rotary and sugars in nucleic acid laevo-rotary)