A ground breaking experiment performed around 1952 by
Stanley L. Miller, that established a plausible mechanism for the origin of
amino acids (the fundamental units of
proteins) from common elements in
primordial earth's oceans and atomosphere.
Carl Sagan once described it as "the single most significant step in convincing many scientists that life is likely to be abundant in the cosmos."
Early earth was an inhospitable place, with massive volcanic activity, constant rain and lightining, and a reducing atmosphere with absolutely no free elemental oxygen. Starting with geological clues on the conditions of the
primordial soup, Stanley Miller, then just a graduate student, and his Nobel prize winning supervisor,
Harold C. Urey decided to experimentally test whether such conditions could have created the stuff of life.
Creating a closed piece of glassware with two large chambers (representing the
atmosphere and the
ocean), Miller filled the ocean chamber with water, and kept it boiling. The atmosphere was filled with
methane,
ammonia and elemental
hydrogen gas. In the atmospheric chamber of the apparatus, electrodes pounded the gasses with electrical discharge, to simulate lightning. During the first day, the water in the "ocean" became noticibly pink due to organic compounds adhering to the
silica glass. By the end of the day, the mixture was deep red and turbid.
Prepping this mixture, Miller found that 13 of the 20 amino acids could be purified. When Miller presented these findings at a conference,
Enrico Fermi stood up at one point and asked if it was known whether such a process could have actually taken place on primitive earth. Urey intercepted the question, stating "If God did not do it this way, then he missed a good bet!".
Since its publication in Science in 1953, this experiment has been repeated and amended many times in research labs and high schools. Recent geological evidence has begun to challenge some of Miller's assumptions. Importantly, gaseous hydrogen may have been in shorter supply than originally believed and without it, electrical discharge doesn't trigger the right chemistry. Still, workarounds have been developed and the field continues to evolve.
REFS
"A Production of Amino Acids Under Possible Primitive Earth Conditions." Stanley L. Miller.
Science 17, 528. (1953)
"Prebiotic Soup - Revisiting the Miller Experiment" Jeffrey Bada and Antonio Lazcano.
Science 300, 745. (2003)
"Primordial Recipe: Spark and Stir."
Astrobiology Magazine May 23, 2003.