Scientists Investigate A Popular Theory On The Origin Of Life

Chris German, Woods Hold Oceanographic Institution

Something that has been puzzling man for a long time is how life began on Earth. There are many theories which attempt to answer this question, from the idea that life actually began elsewhere and may have been brought here by meteorites, to life starting from an RNA world or a primordial soup. Another popular theory is that life began in hydrothermal vents found deep at the bottom of oceans. Researchers from the Woods Hole Oceanographic Institution set out to find evidence for this theory, but their results demonstrate that things aren’t always as simple as they seem. The study has been published in the journal Proceedings of the National Academy of Sciences

Back in 1977, scientists exploring the Pacific Ocean within a submersible called Alvin made a fascinating discovery at the ocean floor; vents that looked like underwater chimneys, spewing out hot water and minerals into the cold surrounding ocean water. They’re caused by tectonic plate movement and are often found along mid-ocean ridges. But what the scientists also unexpectedly discovered was that these vents were actually teaming with life; in particular, they are home to numerous bacterial and archaeal species that were found to be living off of the hydrogen, carbon dioxide and sulphur released from the vents. Archaea are an ancient life form, and some even believe that they are the most ancient form of life.

Scientists began to wonder whether these vents might have presented the perfect conditions for life to begin. In particular, they thought that the carbon dioxide, hydrogen and sulphide present at in the vent fluids may have been enough to produce a compound called methanethiol, which was postulated to be the building block from which life began. Could methanethiol be responsible for the giant stride from a chemical to a living world? Methanethiol is a sulphur containing compound that is naturally found in humans, animals and plants, and is actually responsible for the smell of farts.

The scientists began collecting vent fluid from various different areas to test the concentrations of methanethiol present. They predicted that the more hydrogen that was present, the more methanethiol they would find. Intriguingly, the hydrogen-rich environments had very little methanethiol; conversely, areas low in hydrogen seemed to contain more. This suggested that current theories on the synthesis of methanethiol are outdated.

Interestingly, what they did find was that the breakdown of pre-existing microbial life by the hot vent fluids caused an increase in the abundance of methanethiol, suggesting there may be a surprising amount of life below the seafloor. Taken together, these results suggested that abiotic (without life) synthesis of methanethiol at these is unlikely.

Although this may seem disappointing to some, on the flip side, the results suggest that methanethiol could now serve as a marker for life on other planets which possess hydrothermal vents, which is exciting. It’s also still a possibility that life began at these vents through other mechanisms as they do fit the bill quite nicely, but scientists haven’t quite cracked it yet. 

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