Volcanic lightning may have sparked life on Earth

One of the most famous experiments of all time has just been found to have been even more successful than anyone realised. The Miller-Urey spark flask experiment could hold the key to the origin of life on Earth.

Jeffrey Bada of the Scripps Institution of Oceanography in California and colleagues re-analysed the original 50-year-old samples left by Stanley Miller of the University of Chicago, in 1953 and 1954. His was the first experiment ever to produce amino acids, the building blocks of proteins, from inorganic molecules and a spark of electricity.

Bada’s team discovered more organic molecules than Miller had been able to detect, and also showed that a secondary experiment – one that Miller carried out but never published – offers the best clue to how life on Earth began some 4 billion years ago.

Old boxes

Miller died in 2007 and Bada, who had been one of his first students, inherited the contents of his office and lab. A chance conversation made Bada open the boxes earlier this year. “We found extracts from each of the experiments. All of a sudden I realised, here we had the original samples in our hands that we could reinvestigate using modern analytical methods that Stanley did not have at his disposal at the time.” (Listen to Bada’s account of the samples’ re-discovery in the video clip at right.)

In the classic Miller-Urey experiment, a mixture of gases and water that Miller thought were present on early Earth was heated and zapped with electricity to mimic lightning. This created five identifiable amino acids.

Yet Miller tested three versions of his spark flask. One of the two lesser-know setups – the volcanic apparatus – created 22 amino acids that could be positively identified.

Extra steam

The volcanic apparatus is only slightly different to the classic design. A narrowing in one glass tube increases the flow of steam that passes through the electrical current. That small variation, however, makes all the difference.

“The experiment not only produced a richer mix of amino acids but many of the amino acids are ones that have never been detected in a simulated early Earth experiment,” says Bada.

What’s more, “many of these other amino acids have hydroxyl groups attached to them, meaning they would be more reactive and more likely to create totally new molecules, given enough time”, adds Adam Johnson of Indiana University, who collaborated on the project.

Electric volcanism

One criticism of Miller’s experiment is that he got the atmosphere of early Earth slightly wrong. The new discoveries could give it a second life. The conditions in Miller’s flasks may not replicate the ones covering the entire surface of Earth, but they could have been found in small regions around the planet. According to Bada, Miller’s gases could have been spat out by the many volcanoes that dotted the planet at the time.

All that would then be needed is electricity – and many large volcanic eruptions are accompanied by spectacular lightning. This was the case, for instance, when the Chaitén volcano in Chile erupted for the first time in 9000 years in May 2008 (see image, right).

“Instead of Darwin’s warm little pond being the entire ocean, the warm little pond could have consisted of volcanic island tide pools and lagoons,” says Bada.

Why would the bit of extra steam in the volcanic apparatus make such a great difference? One possible explanation is that the steam pushes newly formed amino acids away from the sparks before they are able to react further and form other compounds.

“This is an exciting result leading toward greater understanding of how life might have arisen on Earth,” says Carl Pilcher, director of the NASA Astrobiology Institute.

The findings could also give clues to life on other planets. The conditions found in the volcanic spark flask could conceivably have once existed on Mars or Titan, and Bada is developing instruments that could detect tiny amounts of amino acids frozen beneath the surface of the Red Planet.

Journal reference: Science (DOI: 10.1126/science.1161527)

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