Searching for a molecule that could have powered the first life forms, researchers have proposed hydrogen peroxide (H2O2), best known to non-chemists as hair bleach. When reacting with thiosulfate (S2O32-), hydrogen peroxide releases energy that fits a lot of requirements for the mechanism that powered the first stirrings of life.
Even before the first cells appeared it is believed that RNA molecules grew and multiplied, eventually laying the foundations for more complex life forms. This “RNA world” is thought to have originated around hydrothermal vents at the bottom of the ocean. Volcanic heat supplied the energy that life needed to grow, just as sunlight does today. However, there had to be some chemical way to capture and process this energy, and the nature of the chemical reactions involved has been the source of much speculation.
In the Royal Society Interface, Dr Rowena Ball of the Australian National University proposes that hydrogen peroxide fits all of the requirements. While we manufacture millions of tons of H2O2 for everything from making plastics to bleaching hair, it also exists naturally, and, Ball pointed out to IFLS, has also been found in space.
Ball told IFLS that, “A whole range of sulfates are and were ubiquitous on the Earth,” and a variety of these may have reacted with hydrogen peroxide in suitable ways. Ball chose to study the interactions with thiosulfate, “Because we had the best data on it.”
Ball conducted computer modeling on the H2O2/S2O23- reaction using ten coupled linear equations that took months to solve. What she found confirmed the suitability of the reaction as a potential energy source in the RNA world.
Moreover, Ball says, a number of features of the chemicals make them particularly likely suspects.
“Waves of acidity and heat could spread away from the original heat source, which would liberate life from narrow regions around hydrothermal vents," she said, explaining to IFLS, “Submarine vents are a suitable place for life to evolve, but it is potentially restricted to a narrow environment close to the vent. Hydrogen peroxide produced in sufficient quantities can radiate in thermal waves, so you immediately have a mechanism that liberates life from that specialized environment.”
Ball also reports that when powered by this mechanism, “Longer [RNA] strands are fitter.” She explained to IFLS. “RNA can catalyze its own replication, but needs to fold itself into the appropriate form, and the longer the strand is the better it can do this.”
The creation of longer strands represents a step toward the subsequent complexity. Moreover, Ball noted, “Hydrogen peroxide has just enough oxidizing power to cause mutations every now and then, which would drive evolution."
Hydrogen peroxide is the simplest chiral molecule, coming in two mirror image versions, each of which cannot be superimposed on the other. Ball points out that biochemists remain puzzled as to why life forms only use one version of chiral molecules.
“We are starting to think that in the search for life, one of the biosignatures we should be looking for is hydrogen peroxide,” Ball says.