Foul-smelling hydrogen sulphide may have been an important precursor in the chemistry that eventually led to life on Earth, a new study suggests.
Modern analyses of samples archived from 1950s experiments indicate the gas can, under the right conditions, play a role in reactions that produce some of the building blocks of biology - amino acids, which combine to make proteins.
The findings are based on the work of Stanley Miller who famously tried to replicate the chemical "primordial soup" from which life may have emerged.
Miller's seminal experiments, first conducted in 1953, put an electric discharge across a chamber containing a mixture of water, methane, ammonia and hydrogen.
His simple laboratory set-up was designed to simulate what might have happened if lightning passed through the kinds of gases thought then to have dominated Earth's oxygen-free atmosphere billions years ago.
When his experiments resulted in the production of amino acids, it was a startling discovery.
Later experiments that injected hot steam into the mix generated an even richer blend of organic (carbon-rich) chemistry.
Miller died in 2007 and all his materials - including notebooks and several boxes containing vials of dried samples from his experiments - were given to a former student, Jeffrey Bada.
Bada is affiliated to the Scripps Institution of Oceanography, in La Jolla, California.
He and his research team are now working through the Miller archive to see what chemical treasures it holds.
The new findings, reported in the PNAS journal, come from the results of experiments Miller did in 1958 but which he himself never analysed and wrote up.
In these tests Miller had altered his early-Earth atmosphere to include some hydrogen sulphide, which most people know as "swamp gas" or "rotten eggs" for its stench.
Jeffrey Bada and colleagues subjected the archived residues produced in these experiments using high-performance techniques that were not available in 1958 and which are billions of times more sensitive than any analytical tools Miller could have deployed.
Professor Bada's team identified a total of 23 amino acids and four amines, including seven organo-sulphur compounds in the residues.
The researchers say these results support the claim that early Earth volcanoes - which can spew vast quantities of hydrogen sulphide - accompanied by lightning could have converted simple gases into a wide array of amino acids, which were in turn available for assembly into early proteins.
"What really came out of it that struck me immediately was that the diversity of amino acids in this experiment is far greater than in any other experiment he ever did," Professor Bada told BBC News.
"So, H2S clearly causes some additional interesting chemistry to take place; it results in the production of a larger variety of amino acids."
The team also compared the amino acid mix in the archived residues to that found in the Murchison meteorite, a famous and very primitive space rock that fell to Earth in 1969. There are strong similarities, says Professor Bada, which adds further support to the idea that some of processes that give rise to the pre-biotic chemistry championed by Miller are widespread in the Solar System and beyond.
To see some historic chemistry experiments continue to provide new insights is fascinating - and there may be more to come.
"Even up to 1972, Stanley had saved extracts from his experiments," explained Professor Bada.
"There must be over 200 vials in this collection and we've analysed only probably two dozen. The sad part of this is that I discovered this collection of samples right after he'd had a completely disabling stroke; he was unable to communicate. And I never had the opportunity to say, 'Stanley, you saved all these things and we're going to analyse them."
"You've got to remember that for him analysing these residues took perhaps a week; for us, we can do the same amount of work in just 15 minutes."
No-one knows how life originated on the early Earth, but it has become a popular theory that the mechanisms and ingredients were here - perhaps supplemented by bombarding comets and meteorites - to get biology moving.