Knowledge · Praktiker
The Miller-Urey Experiment Explained Simply
On this page
Can the stuff of life arise on its own from dead chemistry? In 1953 two researchers put exactly this question into the lab. Their result surprised the whole world.
What the experiment showed
Stanley Miller and Harold Urey recreated the early Earth in a glass flask. They filled it with simple gases and sent electric sparks through it, like lightning in a primordial atmosphere.
After a few days the liquid changed color. In it were amino acids, the building blocks of proteins. These building blocks had formed on their own.
How the setup worked
The apparatus was a closed loop. Water was heated, the vapor rose and mixed with the gases.
The sparks supplied the energy for the reactions. Then everything cooled, and the new substances gathered at the bottom, much like rain in a primordial soup.
Which building blocks emerged
At first Miller detected a few amino acids. Later analyses of the old samples found many more different molecules.
So it was clear: even simple conditions suffice to form important building blocks of life. The first step needs no miracle.
Why it became so famous
The experiment turned the origin of life into a measurable question. Before it was pure speculation, afterwards a field of research in the lab.
It showed a path from chemistry to biology. What came next is covered by the RNA world hypothesis.
What we view critically today
The assumed early atmosphere is now thought to have a different composition. That weakens the original picture a little.
But the building blocks form under newer conditions too, for example at hydrothermal vents. The core message holds, as the origin of life section shows.
Frequently asked questions
Did the experiment create life?
No. It only created building blocks like amino acids, not life. But it showed that these building blocks can arise all by themselves from simple substances.
Were the assumed gases of the early Earth correct?
The exact composition is now thought to be different. Yet the building blocks still form under newer assumptions too, for example at hot vents on the seafloor.
Who ran the experiment and when?
Stanley Miller and Harold Urey carried it out in 1953 at the University of Chicago. Miller was still a doctoral student at the time.
Which building blocks formed in the experiment?
Amino acids formed, the building blocks of proteins. Later analyses of the old samples even found far more diverse organic molecules than originally reported.
Which gases did Miller and Urey put in the flask?
They used a mix of methane, ammonia, hydrogen and water vapor. These gases were then thought to be typical of the young Earth's early atmosphere.
Why was the experiment so important?
For the first time it turned the origin of life into a question that could be measured in the lab. That changed pure speculation into a researchable field.
Sources and further reading
- Origins of Life — NASA Astrobiology
- The Miller-Urey Experiment — Science
Update note (as of: 06/04/2026)
First publication of the Miller-Urey experiment spoke.
The cosmos in your inbox
Once a week: the best of the universe, made simple.