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How did the Miller-Urey experiment simulate conditions on early Earth?

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A herd of African elephants stands at the edge of the Chobe River in Botswana, drinking water with a backdrop of dry hills and scattered green trees. — life A herd of African elephants (*Loxodonta africana*) drinking from the Chobe River, Botswana.

The Miller-Urey experiment was designed to test the hypothesis that organic molecules could form abiogenically from inorganic precursors under conditions thought to represent early Earth. To simulate these conditions, researchers constructed a closed glass apparatus that modeled the interaction between a primitive atmosphere and oceans.1

The simulation incorporated several key features:
* Atmospheric Composition: The system was evacuated and filled with gases—primarily ammonia, methane, and hydrogen—to replicate a "reducing" atmosphere, which was believed at the time to be characteristic of the prebiotic Earth.12
* Hydrological Cycle: A lower boiling flask filled with water simulated the early oceans. Boiling this water produced vapor that circulated into an upper chamber, representing the atmosphere, before condensing and returning to the lower flask.1
* Energy Source: To drive chemical reactions, electrodes were placed in the upper chamber to discharge sparks, simulating lightning as a source of energy.1

After running this cycle for one week, the researchers identified amino acids in the resulting solution, providing evidence that complex organic building blocks could arise from simple inorganic materials.1