The Miller-Urey experiment passed a continuous electrical discharge simulating lightning through a mixture of gases that were thought to make up the early Earth's atmosphere

The Miller-Urey experiment passed a continuous electrical discharge simulating lightning through a mixture of gases that were thought to make up the early Earth's atmosphere.

They used a mixture of methane (##"CH"_4##), ammonia (##"NH"_3##), hydrogen (##"H"_2##), and water (##"H"_2"O"##).

At the end of one week, as much as 10-15 % of the carbon was in the form of organic compounds.

About 2 % of the carbon had formed over 20 amino acids, including 13 of the 22 that are used to make in living cells.

Scientists now believe that the atmosphere of the early Earth was different from that used by Miller and Urey, but their work was a landmark experiment.

It showed that amino acids, which are essential to life, could arise from inorganic precursors.