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Theories on Origin of Life
Many theories have been postulated to explain the origin of life. The views on the origin of life has been putforth as
Special creation: This idea embodies that life on Earth is a divine creation and also attributes to supernatural event at a particular time in the past.It also emphasizes that life has not changed ever since its origin.
Spontaneous generation (Abiogenesis): According to this theory life originated spontaneously from lifeless matter. It was believed that fishes originated from mud, frogs from moist soil and insects from decaying matter.
Biogenesis: It was speculated by Louis Pasteur (1862) that life originates from pre-existing life. He showed that pre-sterilised flasks kept closed airtight, with killed yeast, did not give rise to any life form, while in another flask kept open to air living organisms arose from killed yeast.
Extraterresterial or Cosmic origin: Some scientists still believe that life came from outer space. This states that units of life called spores (Panspermia) were transferred to different planets including earth. This is still an idea of some astronomers.
Chemical Evolution of Life: This idea was developed by Oparin (1922) and Haldane (1929). They proposed that with the conditions prevailing on earth, life arose by a series of sequential chemical reactions. The first form of life could have come from pre-existing non-living inorganic molecules which gave rise to formation of diverse organic molecules which are transformed into colloid system to produce life. The modern concept on chemical evolution regarding origin of life was accepted.
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