In my previous posts, A brave new RNA world and Finding the lifeblood for life, I explored how the proposed antecedent to cellular life, the RNA world, could have emerged through the thermal cycling properties of hydrogen peroxide and thiosulphate. With the help of Associate Professor Rowena Ball, a mathematical chemist from Australian National University, I learned about some of the thermodynamic prerequisites for complex, but still inert, chemical matter to be able to take the plunge in complexity and become organic – that’s to say, alive – matter. For the RNA world to have existed, and scientists are fairly sure it did, it necessitated the presence of an intermittent thermal energy source. Without cellular machinery, RNA needed to receive a heating phase to separate its base-paired double strands and a cooling phase to anneal both strands into a double helix.
Ball’s studies collectively went further than that, however. Not only did they show that a hydrogen peroxide-thiosulphate mixture could have provided the periodic heat energy required for RNA to replicate, but also the pH gradient needed for the proton motive force to help generate power for complex organic activities; it could have also helped life to develop homochirality. Both chemicals were apparently known to cohabitate the primordial soup from which life first spawned. “You can think about it like this: life was really powered by the enthalpy of the peroxide-oxygen-oxygen bond,” Ball summarised.
However, there are many theories competing to explain the emergence of life. Noting that her studies still needed to be experimentally verified – a laborious task that may take months – Ball was still certain hydrogen peroxide has had a strong link to the emergence of life on Earth, and elsewhere in the cosmos. “Everyone knows the formula for water, H2O – [hydrogen peroxide] has just got one more oxygen atom than water, that’s all it is,” she said. “I think it’s inevitable, really [that life would form]. Hydrogen peroxide is ubiquitous throughout the universe, the ingredients of life have been found in meteors – the Murchison meteorite, that landed in Australia about 10 or 20 years ago, has been found to contain in it small biological molecules.”
The biggest irony, Ball reckoned, was that hydrogen peroxide enabled life to get going on Earth, which in due course evolved a creature capable of manufacturing hydrogen peroxide and using it to make vast amounts of plastic – and then dump plastic waste into the earth’s oceans, killing off other life. “It was there in the beginning and as evolution is sort of economical gradually cells evolved and these thermo Hydrogen peroxide oscillators were no longer necessary to drive replication, but it was still around and life found a use for it,” she said.
However, the jury was still out as to whether the complexity of life on Earth would be the same as that in other parts of the universe. Was, for instance, homochirality an emergent property of all life or just life on Earth? “Could there somewhere else in the universe be life forms that are based on L nucleic acids?” Ball asked. “In other words, are we all really vampires, condemned to search for our missing mirror images?” There were also questions surrounding whether the RNA world was the first form of life to come onto the scene or whether simpler information-containing polymers developed first. “But there’s broad acceptance that we had this RNA world; there are just disagreements about whether this RNA world co-existed with peptides and amino acids and sort of developed together,” Ball assured.
What does this all mean for the phenomenon of rising complexity in general? For me, it all reinforced the importance of thermodynamic processes in regulating the energy and information flows needed for complexity to grow. As long as such processes were set in motion by certain threshold-breaking events (for instance, the provision of the thermal cycling needed to energise RNA replication), it was entirely possible for regimes of matter to build upon one another and form emergent regimes with even greater complexity. Cast your mind to the ‘evolution’ of chemical matter: cooked in the furnaces of stars and discharged into the cosmos when they died, complex chemical atoms were created by the thermodynamic reactions of stellar evolution. Then, becoming arranged – as molecules – and organised in myriad ways on planets and meteors gravitating around second-generation stars all over the universe, it was just a matter of time until some combination of chemicals, somewhere, broke through the next threshold and began emerging into organic systems.
In a universe filled with billions of galaxies, each containing billions of stars and gravitationally-attracted planets, and a universal abundance of a chemical which could have provided this threshold-crossing moment in hydrogen peroxide (a simple molecule at that), the probability of matter and energy coalescing to form life was stark, to say the very least. And Ball agreed: “I think we’ll probably find that life did, at one stage, exist on Mars and elsewhere in the solar system. And inevitably, they’ll find out there tens or hundreds of thousands of planets and thousands and thousands in inhabitable zones, so inevitably they’ll find a planet that’s earth-like.”