abiogenesis – some amateur explorations
woteva
One of the greatest mysteries and challenges we face, as living beings – if we’re interested – is how living beings came to be. And we’re the only form of living beings, that we know of, asking this question. Hans Castorp, the central character of Thomas Mann’s The Magic Mountain, pondered the matter in his loggia while taking the cure in an alpine sanatorium. He even went further than the What is life question, asking What is matter? Why is there something rather than nothing?
It was a novel that changed my life. From that reading experience I turned, quite abruptly, to science. I bought Scientific American every month, until I switched to New Scientist, and started reading books by Richard Dawkins, Peter Atkins et al. Of course I’ve never undertaken any formal studies in science, and I’ve always preferred the informal to the formal, and not being subject to authorities telling me what to learn or know. That’s why Hans Castorp, reading and musing in his loggia, so appealed to me.
So what do we know on this subject? When did life begin on Earth, and how? It could have been close to 4 billion years ago, only half a billion years(!) after our planet was fully formed. We don’t have solid evidence, though. The earliest accepted evidence goes back 3.5 billion years, of ‘bacteria-like organisms’. That sounds pretty complex already, and presumably the ‘ingredients’, the intracellular material that sustained and motivated these beings, were around long before. Complexifying chains of molecules, formed out of the ‘primordial soup’, to use an unhelpful term. We think RNA and DNA of course, or at least nucleic acid chains. But what are nucleic acids, and what are the parts thereof? Other essential components include proteins and lipids, with the latter being essential to create more or less permeable boundaries between the organic and the inorganic (or proto-organic?). Lipid molecules, as the Arvin Ash video referenced below tells us, consist of a hydrophilic body, of sorts, and a hydrophobic tail. These molecules tend to come together to form spheres, with the outer, bulkier, hydrophilic ends joining together to protect or insulate the hydrophobic tails from the watery outer environment.
So there’s always a ‘what came before’ question. Where did these lipid molecules spring from, not to mention the other bits and bobs of life? Well, on lipids, I’m relying, for now, on the same video. Carbon monoxide (CO), hydrogen and minerals found in the Earth’s crust can combine to form lipids. All of these components can be found in the hydrothermal vents so recently found in the Pacific depths. But lipid structures break down in the presence of salt or magnesium ions, and these ions are essential for cellular and RNA development. Big problem, as the primeval oceans are believed to be more salty than those of today – though apparently we’re far from being certain about this. In any case, a 2019 paper from the University of Washington showed that lipid spheres remained intact in the presence of amino acids, the building blocks of protein molecules. To quote from the video,
The enclosing of amino acids within cell walls allows them to concentrate within those walls and interact with each other to form proteins, which are part of the ‘trinity’, one of the essential components of life.
So lipid cell walls and proteins, both of course non-living, require each other to survive in salty or iron-rich water. But what about the nucleic acids, DNA and RNA? These are the self-replicating molecules, the genetic material, or precursor genetic material. Today we know that RNA is created from DNA to build proteins according to DNA’s code, but the fact that RNA is the simpler of the two genetic materials suggests to most analysts that it came first. So there’s a hypothesis called the ‘RNA world’, which is generally well accepted by those in the field, but unfortunately we’ve made little progress in working out how RNA came to be formed.
RNA is made up of three chemical components – ribose (a sugar), the nucleobases, and phosphate. A ribose-base-phosphate unit links with other such units to form RNA polymer. But it’s not well understood how these links were formed, and they haven’t been successfully replicated in human experiments. The ribose-base link has proved particularly problematic. As Arvin Ash describes it, ‘this is because cells in your body require complex enzymes to bring RNA building blocks together before they combine to form polymers’. He describes one study, however, which found that today’s RNA could have formed on the surface of clays ‘which act like a catalyst to bring RNA bases together’. A later study showed that the building blocks of RNA could have polymerised in the early Earth, using organic molecules from meteorites and interplanetary dust in shallow ponds, where wet/dry cycles would have been conducive to such polymerisation. They considered that these polymers were probably present on Earth shortly after its formation.
So Ash describes a trinity – RNA, lipids and proteins. What about the proteins? We can go back to the Miller-Urey experiments of the 1950s, which showed that amino acids, the essential components of proteins, as well as other organic compounds, could be produced under particular atmospheric conditions, which they were able to replicate in the laboratory.
So, all these precursors might be explained, but they still need to combine for life as we know it, however basic. This is the big question that still needs to be answered. We haven’t discovered any precise mechanism, but oodles of time, and incremental steps are probably required, and there is surely a possibility of this in the first billions of our planet’s existence, wherein trillions of molecular interactions may have taken place. It’s something of a numbers game, something that many earlier theorists, and today’s creationists, have not taken sufficient account of. It’s also probable that the earliest life forms, those sparks, were so basic that they were quickly improved upon and rendered obsolete by – evolution. But that’s another story…
Needless to say, this piece was more or less wholly reliant on Arvin Ash’s excellent video, which I highly recommend.
References
Why is the Ocean So Salty?
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