

The first to question the theory of "spontaneous generation" scientific methods was the physician Francesco Redi in the second half of the seventeenth century. Redi demonstrated against the widespread view that the flies were born in the putrefaction of meat, which insects born in such places only if you previously had deposited their eggs. Still, even experiments with bacteria by Pasteur (XIX century), in which he demonstrated that living organisms arise only from another living organism, the theory of "spontaneous generation" was not fully refuted.
Currently there are two theories that are more accepted as an explanation for the emergence of life on our planet.
• The first theory claims that life was brought to Earth by meteorites from outer space. Actually this argument does not end solve the question of how it arises life, as it simply says that life is found elsewhere in the universe and our planet came unexpectedly.
• The second theory is that it is harder today. Was developed by the Russian biochemist Alexander Oparin and Haldane scientific colleague, and more recently by the American Harold Urey. According to these scientists the atmosphere of early Earth was comprised mostly of methane, ammonia and water vapor. The lack of oxygen in the atmosphere made us there is no shield for the most active part of solar radiation, so that ammonia, methane and water vapor react with each other due to ultraviolet radiation and thus arose the first organic molecules of which would result after all living organisms.
No doubt this issue will not leave us never to fascinate and future generations will continue to seek the ultimate answer to dilute the mists that hang over the origin of the greatest miracle of the universe: life.
Source:
http://www.mascultura.com/misterios/86-teoria-origen-vida.html