We all know that astronomy is just plain awesome – and pretty much everything that’s interesting in the world links back to astronomy and space science in one way or another. Here I’m thinking gravity, wireless internet and of course ear thermometers. But wouldn’t it be great if we could ascribe the whole origin of life to astronomy as well? Well, apparently we can – and it’s all about cosmic rays.
Three key contenders for how it all started are:
1) Deep ocean vents, with heat, water and lots of chemistry churning away, enabled the random creation of a self-replicating crystalline compound – which, being self-replicating, rapidly came to dominate an environment of limited raw materials. From there, because it was imperfectly self-replicating, particular forms that were slightly more efficient at utilizing those limited resources came to dominate over other forms and yada, yada;
2) Something arrived on a comet or asteroid. This is the panspermia hypothesis, which just pushes the problem one step back, since life still had to start somewhere else. A bit like the whole God hypothesis really. Nonetheless, it’s a valid option; and
3) The Miller-Urey experiment demonstrated that if you zap a simple mix of water, methane, ammonia and hydrogen with an electric spark, roughly equivalent to a lightning bolt in the early Earth’s prebiotic atmosphere, you convert about 15% of the carbon present in that inorganic atmosphere into organic compounds, notably 22 amino acid types. From this base, it’s assumed that a self-replicating molecule came to be and from there… well, see point 1).
Additional support for the Miller-Urey option comes from the analysis of ‘old’ genes, being genes which are common to a wide diversity of different species and are hence likely to have been passed down from a common early ancestor. It’s found that these old genes preferentially code for amino acids that can be produced in the Miller-Urey experiment, being the only amino acids that would have been available to early Earth organisms. Only later did a much larger set of amino acids become available when subsequent generations of organisms began to learn how to synthesize them.
Nonetheless, Elykin and Wolfendale argue that the available spark energy generated in a average lightning storm would not have been sufficient to generate the reactions of the Miller-Urey experiment and that an extra factor is needed to somehow intensify the lightning in early Earth’s atmosphere. This is where cosmic rays come in.
While many cosmic rays are generated by solar activity and most don’t penetrate far into the atmosphere, high energy cosmic ray particles, which generally originate from outside the solar system, can create electron air showers. These arise from a cosmic ray particle colliding with an atmospheric particle producing a cascade of charged pions, which decay into muons and then electrons – resulting in a dense collection of electrons showering down to two kilometers or less above the Earth’s surface.
Such a dense electron air shower could initiate, enhance and sustain a high energy lightning storm and the researchers propose that, perhaps when the early solar system was drifting past some primeval supernova event over four billion years ago, this was what started it all.