The Miller-Urey Experiment

In 1953, Stanley Miller and Harold Urey did an experiment to

test Oparin and Haldane’s ideas, since they found that organic molecules could be spontaneously produced under reducing conditions of early Earth.

Set up:

They built a closed system containing a heated pool of water and a mixture of gases that were thought to be abundant in the atmosphere of early earth (H2O, NH3, CH4 and H2). Sparks of electricity were used to stimulate lightings.

Experiment:

1. Water in a flask (representing the ocean) is boiled so it evaporate and moves into the larger flask, where it combines with methane, ammonia & hydrogen gases (representative of Earth’s prebiotic atmosphere)
2. Sparks are fired between electrodes to simulate lightning
3. A cool condenser turns steam back into liquid, which drips down into a trap, where molecules produced in the reaction can settle for collection.

Conclusion:

Organic molecules (carbon compounds such as amino acids) can form from simple gases in a reducing atmosphere when exposed to energy sources like lightning. So it is possible that life had formed spontaneously from prebiotic Earth!

Limitation: They likely got some conditions wrong, since the composition of gases may be different than originally thought (e.g. more CO2 and N2, less NH3 and CH4 than thought)