Carbonyl sulfide is present in volcanic gasses and deep sea vent emissions today, and since these geological phenomena were prominent features on the early Earth, it is reasonable to assume that the gas was present.
In their report, the scientists demonstrate that the gas can bring about a vigorous chemical reaction that forms peptides under mild aqueous conditions. Within a few minutes of introducing the gas to a reaction vessel containing amino acids, they observed high yields of di-, tri-, and tetra-peptides. They carried out the reaction in the presence of air, without air, and with and without other ingredients like metal ions, and they found peptides formed readily under all these conditions.
“It’s really efficient, actually,” says Ghadiri. “This addresses a very important question that we did not have a real good answer for.”
The question of how life originated is one of the most interesting gaps in our knowledge–interesting perhaps because we know approximately when it occurred, but we do not know how it occurred.
The earliest fossils scientists have found are stromatolites–large clumps of cyanobacteria that grew in abundance in the ancient world over 3.5 billion years ago in what is now western Australia. These most likely evolved from some simpler life forms because, like all modern life, cyanobacteria are highly sophisticated living organisms–with cell walls, complex metabolism, and DNA genes. The question of the origins of life is: what came before the stromatolites?
Research on the origins of life has suggested the notion of an ancient RNA world–one in which RNA genes stored genetic information (something done by DNA today), carried out the chemistry necessary for life, and formed the essential physical structures of life (something done primarily by proteins today).
But how did that RNA world come about?
“Anybody who thinks they know the solution to this problem [of the origin of life] is deluded,” says Orgel.
“But,” he adds, “anybody who thinks this is an insoluble problem is also deluded.”
One possible approach to the problem of life’s origins is to ask the question scientifically rather than historically– how can life emerge rather than how did life emerge. In order to address this, scientists try to determine experimentally what is chemically feasible and what could have occurred on the prebiotic earth.
One possibility, which was suggested in the 1920s by the Russian scientist A.I. Oparin, is that life emerged in its most primitive forms from minerals, metals, and the elements carbon, hydrogen, oxygen, and nitrogen, which were combined into amino acids, nucleotides, and the other the building blocks of life under the violent energy of lightning, solar radiation, comet impacts, and volcanic events that were present.
In 1953, this theory was given a boost when a paper was published in Science by Stanley L. Miller, who is Professor Emeritus at the University of California, San Diego. In the paper, Miller described an experiment he devised with Harold C. Urey–now called the Miller and Urey experiment–that gave experimental underpinnings to Oparin’s ideas.
In the experiment, Miller boiled H2O, CH4,H2, and NH3 gases in a glass apparatus containing a pair of tungsten electrodes. He subjected the chemicals to an electric discharge, intended to simulate conditions on the early Earth, and he collected and analyzed the molecules that formed–which included the amino acids alanine, glycine, and a few others. In the years since, several other investigators have expanded on the Miller?Urey experiment to demonstrate the formation and chemistry of many of the common biological amino acids, sugars, and nucleotides. Orgel, who is a long-time investigator in the field, has done pioneering research on the prebiotic chemistry of nucleotides.
This latest study is an advance because previous attempts to demonstrate the formation of peptides on early Earth depended on reaction schemes that were less plausible or were not as efficient. Next, the team plans to examine carbonyl sulfide’s reactive properties further and see if the gas can bring about other chemical reactions that are relevant to prebiotic chemistry.
On the PBS miniseries Origins which aired a few weeks ago, they profiled a scientist who took a couple of basic amino acids which could have formed on early Earth and smashed them as in a meteorite impact. They used a steel projectile fired at about 5000 mph onto the target, and found that peptides were produced!
It seems as though peptides are becoming a rather natural next step up from amino acids, via several avenues of production.
Pretty cool stuff!
-Mark
This seems to be more fodder for the late Dr. Gold’s theories on the deep biosphere. Perhaps the belly of our planet isn’t such a far-fetched location for the origin’s of life.
One possible energy source for getting prebiotic molecules to react not usually mentioned in the literature (or looked at experimentally) is radioactivity.
Many of the naturally occurring "piles" (old uranium deposits which have big pools of transmuted elements in them, evidence of hit or miss reactor status) also show evidence of quite a bit of biogenic alteration- apparently the little buggers were able to utilize the free beta electron flying about (perhaps also the heat from other radiation as well). Today of course we have electrochemical biomolecules to do this, but perhaps way back then we didn’t.
Because radioisotopes decay differentially, it doesn’t take a calculator to figure out that the less stable isotopes (such as U-235) will be progressively enriched relative to more stable ones as one goes back in time. In fact, in the early earth U-235 relative abundance was HIGHER than in conventional reactor rods.
And because uranium (and presumably other radioisotope and other elemental) chemistry would be radically different in a non-oxygenated atmosphere, instead of dissolving in the sea uranium would cumulate as a sublayer on beaches, along with iron (lighter, so higher up) and other stuff. If one has enough structure to such systems one has a natural chain of materials to modulate the energies produced by the radiactives. Note that iron and other transition metals are at the core of energy transduction in living forms. Add in radioactives and you get a free source of energy, a highly localized and long term one at that.
The beaches would be the place where one would expect the greatest degree of mixing- the sea coming from one side, eroded materials on the other, radiation from below, rain and gases above. And remember that the moon was much closer than it is today, and the core more molten. Therefore much bigger tidal effects.
Undersea fumaroles are much less stably active in any one spot, though an active crust would likely produce a lot more of them than we see today. And meteorites are literally hit or miss.
Freezing can produce peptides (think concentration as in cider) with a little help, as can drying on catalytic minerals. Many sources, many pathways.
But in the end the beaches and river deltas were where the action was, and where materials would be carried at some point in their existance. And in my "hot" early earth, such reactive sand would also be a safe harbor, literally, and figuratively, for the evolution of biomolecules. Oops, forgot cosmic radiation and UV coming from above.
Codemaniac
But where could peptides come from in the first place? Maybe they come from a Scripps Research Institute (SRI) press release
Those Public Relations people are getting a little carried away with how important they have been.