One aspect of the Oparin-Haldane theory that has been neglected so far is the very beginning of life.

Is it reasonable that the organic compounds necessary as the precursors of life would have been synthesized naturally
and abiotically in a reducing atmosphere?

Where would the energy have come from?

The first such simulation experiments were attempted by Harold Urey and his graduate student, Stanley Miller, in 1953. In 1952, Urey had published, in his book The Planets, a survey of the atmospheric chemistry of the planets, and had pointed out the consistently reducing character of their atmospheres.

Miller decided to see if biological molecules could be produced in a mixture of such reducing gases by a spark discharge, as an analog of lightning.

His experimental setup, shown on the next page, consisted of a completely closed system, with gases flowing past a spark discharge; the condensed gases were recirculated by boiling. The gases tried were mixtures of methane, ammonia, water, hydrogen, and other reduced molecules.

The results of a typical run beginning with H2, H2O, NH3, and CH4 are recorded in the graph on the next page.

Ammonia disappeared steadily during the experiment. During the first 25 hours of boiling and refluxing, most of the ammonia and methane was being converted to HCN and aldehydes, with a slow synthesis of amino acids.

During the next 100 hours, HCN and aldehydes reached a steady state, being used in further reactions as rapidly as they were made. The main products from these compounds were amino acids.

They probably were the result of a Strecker synthesis , in which ammonium cyanide reacts with aldehydes to make amino acid nitriles, and these nitriles hydrolyze In water to amino acids.

After 125 hours, as the supplies of ammonia and methane were depleted, HCN and aldehyde concentrations began to decrease. The amino acid concentration leveled off as more of the simple amino acids were incorporated into short peptides.