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How life started?

How did life begin? Even before these blue-greens existed organicmolecules must have evolved. The original atmosphere (see separate page) of the earth was very thin and contained hydrogen, carbon-monoxide, ammonia and methane, but no oxygen. This chemical mixture, together with ultra-violet radiation and frequent electrical discharges causing lightening was simulated in the Miller Urey experiment in the 1950s.

This experiment used water (H2O), methane (CH4), ammonia (NH3) and hydrogen (H2). The chemicals were all sealed inside a sterile array of glass tubes and flasks connected together in a loop, with one flask half-full of liquid water and another flask containing a pair of electrodes. The liquid water was heated to induce evaporation, sparks were fired through the atmosphere and water vapor to simulate lightning, and then the atmosphere was cooled again so that the water could condense and trickle back into the first flask in a continuous cycle.

At the end of one week of continuous operation, Miller and Urey observed that as much as 10-15% of the carbon within the system was now in the form of organic compounds. Two percent of the carbon had formed amino acids, including 13 of the 21 that are used to make proteins in living cells, with glycine as the most abundant.

A diagramatic representation of the Miller-Urey experiment which attempted to synthesized some of the building blocks of life based on our understanding of the earths first environmental conditions.

Archives: Original article

Miller S. L., (1953). Production of Amino Acids Under Possible Primitive Earth Conditions, Science, 117: 528.