Here’s a paper that probably doesn’t have much relevance out here in the real world, but illustrates some of the problems that we do face. Everyone remembers the Miller-Urey experiment, where a mixture of “primordial” gases (water, methane, ammonia, hydrogen) was subjected to repeated electric sparks and heat in a closed vessel. The idea was to see what sort of compounds might have been able to form in the early stages of Earth’s atmosphere, and it richly vindicated the ideas of J. B. S. Haldane and Alexander Oparin that complex chemicals could have been produced under such simple conditions. Famously, a variety of amino acids and other species were formed, and the number of compounds grows every time someone looks at such mixtures with more sensitive analytical techniques.
It’s quite possible (indeed, likely) that the prebiotic Earth had a different ratio of gases than the original experiment used, but followups invariably still produce amino acids and a “soup” of other compounds. The paper linked to above, from a group at Glasgow, runs a variation that Urey himself would have loved. It replaces all the starting materials with their deuterated forms.
As the chemists in the audience will appreciate, that can indeed make a difference. If the rate-limited step in a chemical process involves the breaking or formation of a bond to a hydrogen atom, that reaction will slow down if you use the heavier deuterium instead (which is the whole basis behind using deuterated drugs to slow down metabolic clearance). So what happens in this case? It turns out that you get the suite of amino acids, more or less as before, but a number of the other components of the mixture change. Dozens of compounds that are present in the “normal” runs aren’t there any more, and dozens of new ones are formed. The additive effect of tweaking those bond-breaking and bond-forming reactions sends things into completely new bins (at least 120 new species in all).
I know that the popular picture of the universe (well, one of the popular pictures) is of this vast, cold, empty, airless space, dry and deserted. And while there’s plenty of that out there, from another perspective, the universe is absolutely soaking with water and with what we think of as the molecules of life. All those old science fiction movies about desperate aliens coming to Earth to steal our water? Load of crap. There’s plenty of water out there. Saturn’s rings are made out of chunks of ice. The satellites of Jupiter have way more water than Earth ever could. Comets are snowballs, and Pluto is layered in ice. And along with that water, there’s plenty of methane, hydrogen, ammonia, nitrogen, and all the other simple gases you can name, and these mixtures have, over time, been heated, chilled, mixed, irradiated up and down the electromagnetic spectrum, exposed to all sorts of mineral surfaces, and zapped by gigantic electrical discharges. This latest work just tells us that the variety of compounds formed out there might be even greater than we thought, depending on the isotopic ratios that a given planet or system started out with.
The Miller-Urey experiment (with countless variations) has been running for billions of years, in other words, and when you see the colors of Jupiter and Saturn’s clouds (for example), you’re seeing the results. Those should remind organic chemists of the colorful stuff that sticks to the top of a chromatography column, and indeed, it’s probably pretty similar gunk. Amino acids, carbohydrates, nucleotides and other biomolecules are everywhere, from the insides of comets to interstellar clouds. So when we find our own biochemistry using these species, we should not be amazed, and when we eventually find other forms of life doing the same, that shouldn’t come as a surprise, either.
The surprise might be if we’re not deathly allergic to them – that would have made for some pretty odd Star Trek episodes, if Kirk and Spock beamed down to a new planet and immediate started sneezing their heads off and swelling up with anaphylactic shock. I guess we’ll deal with that problem when we get to it!