Dateline: 4.35 billion years ago.
RNA forms spontaneously on basalt glass!
This incredible feat of synthesis went unremarked at the time because there was, of course, no sentient somebody to remark it. Four and a third billion years is very far back in the distant past, and RNA is an exceedingly ancient molecule.
Scientists have been wondering ever since there were scientists, how life arose on Planet Earth. Convoluted theories involving complicated chemistry and lightning strikes have been proposed, but researchers have not been completely convinced that these complex reactions could have occurred naturally.
In a breakthrough study, scientists at the Foundation for Applied Molecular Evolution have applied the KISS* theory to the question and developed an incredibly simple model to explain how RNA came about. The story from RNA to living organisms then becomes almost inevitable.
Just in case you haven’t spent your formative years in a bio lab, a little background. RNA, or ribonucleic acid, a complex molecule necessary for life, has three components: ribose sugar, nitrogen-containing bases, and phosphoric acid in a chain of three (triphosphate)
The sugar and acids bind tightly together in long helical coils; from each sugar hangs a base. The bases, named adenine, guanine, cytosine and uracil, are also able to attach to one another in endless ways, forming all sorts of three-dimensional shapes – lumpy balls, helices, and bendy strings. The shape of any particular RNA determines its function, making it a chemical workhorse.
DNA, on the other hand, although made up of about the same stuff, is a more structured, more complex, but less adaptable molecule, more like the office filing cabinet than the busy CEO. It stores information. Peptides, strings of linked amino acids, make wonderful catalysts, but lack the ability to reproduce themselves, a must for living creatures. Versatile RNA can catalyze reactions, store data, and reproduce itself; ergo, RNA must have been the starting molecule for what later became life. Good conclusion, but a question still exists. Whence came RNA?
Hadean (very early) Earth was truly a hellish place – volcanos, molten lava flows, meteorite bombardment – not a place you’d want to spend your vacation. It was, however, a place where basalt and diabase rocks were melted into glass, and the glass contained a tiny bit of water in its pores. Could RNA have formed on or in this glass? The KISS study proved that indeed it could, provided that all the requisite molecules were present.
*KISS = Keep It Simple Stupid
Earlier this year, Japanese scientists, using a mild extraction technique – think sun tea rather than roiling kettle – found every base plus ribose sugar in meteorites from North America and Australia. Lava glass, plentiful on Hadean Earth, contains phosphorus. Basalt rock contains boron, which aids in the formation of both ribose and triphosphates. With all its individual bits and pieces present, active RNA might form spontaneously from its parts, with basaltic glass as a catalyst. This, indeed, is what the molecular scientists found in their remarkable study. They put all the individual pieces together, heated them up, and got ribonucleic acids. Furthermore, as their experiment progressed in time, the RNAs continued to grow and were stable.
RNA that can reproduce itself is still very distant from life itself. A true living organism did not appear for another billion or so years. That is LUCA, the Last Universal Common Ancestor, and her story is one for another day.
BTW, all of the necessary elements are also present on Mars, so the story of LUCA may become a twice-told tale.