The origin of life revisited

The 1952 Miller-Urey experiment synthesised amino acids essential to life from inorganic materials. The experiment’s vials were then sealed, and when scientists re-examined them 55 years later they were surprised at what was inside.

Miller-Urey experiment
Carny / CC BY

I’m just going to get this out of the way right away: no, there was not a small but perfectly formed 55-year-old miniature civilisation inside. Sorry if this disappoints you.

The question of how life could emerge from lifelessness – abiogenesis – is a core question of both biology and chemistry. In 1952 a couple of scientists decided to conduct an experiment to shed some light on this process. Stanley Miller and Harold Urey’s experimental design was elegant in its simplicity: recreate the conditions of the early Earth in a sterile environment and see what happened.

So what were those conditions? At the time, the early planet was believed to be a morass of water, methane, ammonia, and hydrogen, lit up by occasional flashes of lightning. So Miller and Urey sealed all the ingredients up in a series of flasks and connected them together. The water was evaporated and the resulting water vapour combined with methane, ammonia, and hydrogen. The whole mixture was zapped with electrodes and then allowed to cool. The result was a landmark discovery: testing revealed organic compounds in the form of five amino acids. The inorganic was made organic. The building blocks of life had emerged from lifelessness.

Miller died in 2007, and amongst his belongings were the original vials from those 1952 experiments. Testing techniques had improved in the intervening fifty-five years, so the vials were retested. Miller and Urey knew they had created five different amino acids… but unbeknown to them, the vial in fact contained more than twenty-five. The standard genetic code that is the basis of all life only needs twenty of these amino acids, so this landmark experiment actually succeeded beyond what anyone at the time knew.

We now think that the conditions of early Earth are a little different from those assumed in the Miller-Urey experiment. If anything, they were more conducive to the creation of amino acids than was assumed at the time. There’s still a lot that we don’t know about the exact processes through which life emerged on this planet, but this experiment put us well on the way to figuring it out.

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