Stanley Miller: Theory, Experiment & Apparatus

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  • 0:01 Who Was Stanley Miller?
  • 0:32 The Miller-Urey Experiment
  • 2:37 The Implications and…
  • 4:09 Miller's Legacy
  • 4:41 Lesson Summary
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Lesson Transcript
Instructor: Mary Ellen Ellis
How did life originate on Earth? We may never have a complete and definite answer to that question, but in 1953, chemist Stanley Miller conducted a famous experiment that would show how the early Earth could have produced the chemicals of life.

Who Was Stanley Miller?

Stanley Miller was an American chemist who conducted one of the most exciting experiments in modern science. It sought to answer the question, How did life on Earth begin? It's a complex question, and one that has still not been fully answered and may never be. Miller's famous experiment, though, gave us an idea of how life could have developed out of non-living matter, a process called abiogenesis.

The Miller-Urey Experiment

Miller's experimental interests at the University of Chicago were in the field of astrobiology, which is the study of life in the universe, including its origins and evolution on Earth, as well as, potentially, elsewhere. The famous experiment Miller conducted in 1953 was based on a hypothesis that stated life could have originated from basic molecules present on the early Earth. The idea was that gases present in the atmosphere and in the seas of the primitive, pre-life Earth could have been stimulated by lightning to react and produce the chemicals necessary for living cells to arise.

Stanley Miller, under the guidance of Professor Harold Urey, set up the Miller-Urey Experiment to test this hypothesis. He included basic chemicals that were present on Earth before life began: water, methane, ammonia, and hydrogen. These molecules contain the most abundant elements in living cells, which are carbon, hydrogen, oxygen, and nitrogen.

Miller connected two sterile, glass flasks by a series of glass tubes. One flask contained water and the dissolved molecules. This flask was heated, and the water vapor and gases released into the tubing. They could freely move into the second flask, which was sparked by electrodes to simulate lightning strikes. The gases were then condensed into a liquid that was carried back to the original flask. The cycle went on continuously for two weeks.

Within one day the solution in the flask had developed a pinkish hue. By the end of the experiment, Miller and Urey identified many new compounds that formed in the apparatus. These included several different types of amino acids, the small molecules that make up proteins, as well as simple carbohydrates.

The Implications and Continuing Work

The results of the Miller-Urey experiment were thrilling for scientists, and the implications were important. Miller proved that under the conditions present on the early Earth (as far as were known at the time), the building block molecules of life could form. Furthermore, we now know that early Earth's atmosphere contained a few more simple compounds that Miller didn't include in his original experiment. These additional molecules would lead to a greater diversity of amino acids and other chemicals found in living cells.

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