A Production of Amino Acids Under Possible Primitive Earth Conditions
Pass a spark through the gases of the young Earth, and the building blocks of life assemble on their own.
In 1953 a graduate student filled a glass loop with the gases of the young Earth, ran a spark through it for a week, and watched the water turn into a broth of the molecules that life is made of.
The big idea
Life is built from a small set of molecules — among them the amino acids that link up into proteins. For a long time it was a mystery how the very first of those molecules could have appeared on a lifeless planet, with nothing alive around to make them. Stanley Miller showed they didn't need anything alive: give the right gases an energy source, and they make themselves.
He recreated a guess about the early atmosphere — methane, ammonia, hydrogen and water — sealed it in glass, and zapped it with a continuous electric spark to stand in for lightning. Within days the clear water had turned a murky red-brown, and floating in it were real amino acids. The building blocks of life had assembled out of plain chemistry.
How it came about
The idea that life began in a chemical “primordial soup” had been floated in the 1920s by Alexander Oparin and J. B. S. Haldane, but it stayed a story for thirty years because no one had tested it. In 1952 Miller, a 23-year-old graduate student, asked his supervisor — the Nobel chemist Harold Urey — to let him try. Urey thought it a long shot, a risky thing to stake a PhD on.
Miller built the apparatus himself and let it run. The transformation was visible to the eye within a day. When he published in 1953, under his own name — Urey insisted the student take the credit — the result made headlines: a young man had, in a sense, cooked up the ingredients of life on a bench in Chicago. It became one of the most famous experiments of the century.
Why it mattered
It moved the origin of life out of pure speculation and onto the laboratory bench. After Miller you could ask precise questions — which gases, how much energy, which molecules — and get measurable answers. It did not show how life began, but it showed that the first and most daunting-seeming step, making life's building blocks from dead matter, is something ordinary nature does readily. That single demonstration reshaped how scientists, and everyone else, picture where we came from.
A way to picture it
Think of the early Earth as an enormous kitchen left running unattended: simple gases for ingredients, oceans for a mixing bowl, lightning for a stove. Nobody is cooking. Yet the heat and the stirring, repeated over and over for ages, are enough to combine the raw ingredients into something more — the way a pot left simmering long enough thickens into a sauce. Miller simply shrank that kitchen into a flask and sped up the clock.
Where it sits
Miller's spark links two long stories in this Library. Behind it stands Darwin, who privately mused that life might have begun in “some warm little pond”, and Oparin and Haldane, who turned that musing into the soup hypothesis. Ahead of it run the molecules of heredity — Watson and Crick's DNA, Crick's central dogma — and the still-open question of how a soup of building blocks ever crossed the line into something that copies itself. Seventy years on, that crossing remains the frontier; Miller showed only, but decisively, that the journey's first step is easy.
The idea that the organic compounds that serve as the basis of life were formed when the earth had an atmosphere of methane, ammonia, water, and hydrogen … was suggested by Oparin and has been given emphasis recently by Urey and Bernal.
A mixture of gases, CH4, NH3, H2O, and H2, which possibly made up the atmosphere of the Earth in its early stages, has been subjected to spark and silent discharges for times of the order of a week.