In 1952 graduate student Stanley Miller carried out his now famous spark-discharge experiment designed to test the Oparin-Haldane hypothesis that biological molecules as the precursor to life could have been created by lightning discharges in the atmosphere of the early Earth.

Miller did find that the discharge could produce amino acids. Including the analysis of some of his experimental chambers after his death, there were about 20 different amino acids in the residue left by the process.

Finding a pathway to amino acids was indeed a crucial step toward understanding life chemistry since they are used to build up proteins in cells by the processes of transcription and translation. The Miller-Urey experiment along with the discovery of DNA structure did lead to great optimism in the 1950's about discovering a chemical pathway to life.

Oparin (1924) and Haldane (1929) independently hypothesized a scenario for the building of the chemical building blocks of life. Oparin in 1936 discussed further steps that would lead to an origin of life from non-living material, which is popularly called "abiogenesis". The illustration at left summarizes the steps of what has been called the Oparin-Haldane Hypothesis for abiogenesis.

Phospholipids and some other compounds do spontaneously form membranes and even vesicles, but most of those molecules that we observe doing that are themselves of biological origin, so they form a chicken-and-egg problem.

The scenario depicted here suggests that nature spontaneously overcame the hurdles of creating a metabolism and the problem of self-replication. Current research follows either the metabolism-first or replicator-first scenarios, and both have encountered major hurdles.