Hydrogen peroxide – hair bleach – in hydrothermal vents may have been the critical ingredient that led to the emergence of life on Earth between 4.2 and 3.8 billion years ago.
Research by Rowena Ball of the Australian National University’s Mathematical Sciences Institute, and John Brindley of the University of Leeds, UK, refreshes and extends one of the two competing theories that aim to explain “abiogenesis”, the emergence of living systems from the prebiotic soup present on the young Earth. One school of thought favours deep ocean hydrothermal vents as the crucibles that led to the formation of RNA (and later, DNA), while the other sees the conditions found in small warm ponds as the likely start-point.
In a paper published in the journal Royal Society Open Science, Ball and Brindley come down heavily on the side of the vent theory, adding important new information about chemical interactions and temperature variations to underpin earlier research.
To make their findings, the team re-examined and extended research modelling the interaction of chemical compounds, porous rock and temperature fluctuations. The modelling suggested that hydrogen peroxide and another compound, thiosulfate, played a crucial role in catalysing reactions inside hydrothermal rock pores to create simple molecules known as monomers, dimers and short polymers.
In an important elaboration of previous research, the scientists found that predictions arising from the chemical reactions occurring in a single rock pore were very different to those that arose when the modelling was widened to take in multiple and interconnected pores.
The existence of long and networked pores allowed for the creation of extended polymers – critical components for the emergence of RNA. Variation in the size and positioning of the pores also turned out to be very important – because this made possible the type of temperature variation that is necessary for polymer formation. (Sustained high temperatures would cause essential catalysts to be destroyed before fulfilling their necessary functions.)
Conditions for the creation of long polymers within the optimum range of temperatures, conclude Ball and her colleague, are better met by hydrothermal vents than the crater lakes favoured by the “small warm pond” hypothesis. Borrowing from astrobiology, the scientists term this confluence of conditions at vents the “goldilocks zone”.
The researchers also find that the emergence of life was perhaps not so remarkable as generally assumed. Their modelling finds that “the dice on the primordial Earth were loaded in favour of the emergence of life,” characterising this as “a profound insight, and perhaps a profound anti-climax … or even a profound existential putdown, given our anthropocentric vanities”.
The research, they suggest, holds value not just for the emergence of life on this planet, but also on others. It provides a possible key new diagnostic tool for assessing the possibility that any planet (or moon) hosts some form of biologic system.
The current hunt for extraterrestrial life is based on the maxim “follow the water”. Ball and Brindley offer a second criterion: “follow the temperature fluctuations”. Planets observed to have too little or too large variations in temperature equilibrium, they say, could quickly be dismissed as candidates for life “and we need not waste further time or money on them”.
Andrew Masterson is a former editor of Cosmos.
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