How life is originated

         Origin of life on earth 

How did life originate

·  The only serious hypothesis entertained by scientists is that life evolved spontaneously by a process of chemosynthesis.

·   This idea of spontaneous generation from nonliving matter was first postulated by the Russian scientist A.J. Oparin and the English scientist J.B.S. Haldane.

·   According to this hypothesis over a long period of time inorganic chemicals on the surface of the earth were transformed into simple organic chemicals in shallow pools of water. These organic chemicals in turn aggregated into more complex units. Long polymers of amino acids and nucleotides could have been part of these complex microscopic structures. Ability to replicate themselves and catalyze various chemical reactions would have made these structures the most primitive living things.

·   Because RNA could store and transmit hereditary information and also catalyze some chemical reactions scientists believe that RNA rather than DNA might have been the genetic material of the earliest organisms.

·   There is evidence that simple organic compounds could have been produced from inorganic matter without the activities of living things. Alcohols, sugars. amino acids and nitrogen bases have been extracted from the interior of meteorites.

·  Experimental evidence for the origin of organic compounds from inorganic substances was demonstrated by S. Miller in 1953. He allowed steam to interact with reducing chemicals such as methane, hydrogen and ammonia in a closed container.

·   Earlier earth conditions: There was no free molecular oxygen and the atmosphere was anaerobic. The surface of the earth was reducing because of the presence of such reducing substances as hydrogen sulphide, methane and ammonia. Temperature in the prebiotic environment was very high, perhaps about 500°C. There was abundant water vapour and high pressure.

·   Later conditions on earth: During the course of evolution of life chlorophyll a evolved in some organisms. Only at this stage light energy from the sun was used to split water and release free oxygen as waste product. Over long periods oxygen accumulated and transformed the atmosphere into an oxidising one. Oxygen could then be used in respiration to release more energy and this was partly responsible for the evolution of structurally more complex organisms.