Now I’m a big fan of alternative biochemistry theories in the search for extraterrestrial life. It seems logical to think that given the size of the universe and the number of possible environments out there, life might have found more than one way to organise itself. However, thanks to some clever thermodynamics, it looks quite likely that at least some alien life out there might not be so “alien” after all…
Ever since the famous Miller-Urey experiment, it’s been known that amino acids, the building blocks of proteins, can be formed with relative ease by simple natural processes. In the experiment, 10 of the 20 amino acids used by life were created readily in conditions mimicking the atmosphere of the early planet Earth. Other theories of abiotic amino acid synthesis include interstellar environments such as molecular cloud cores and protostellar disks, as well as hydrothermal vents (though the latter idea is still disputed).
Higgs and Pudritz (McMaster University, Canada), in this paper, show that those same 10 amino acids are created readily, regardless of the source. The reason? Simple thermodynamics! In fact, thermodynamics can predict the order of abundance of those molecules. It can predict it so accurately, in fact, that a nearly exact match is evident between theoretical predictions and the observed abundances in meteorites. There are lots of things that can be debated in most theories regarding life’s origins, but let’s face it; you can’t argue with thermodynamics. It governs chemistry ubiquitously.
It’s likely then, that the earliest proteins used those 10 amino acids, with the others evolving later — in keeping with evolutionary theories. So the question of exactly where life first started has relatively little impact on the chemistry that life would have used. Fascinating.
The implications are profound. And that isn’t a word I use lightly. Simply, if these 10 amino acids were the basis of life on Earth, and they form so favourably, then there’s a very good chance that life on other planets may have originally used the same ten amino acids. The fundamentals of early biochemistry may well be universal! Now that’s exciting!
Of course, there are countless paths life could take from the same humble beginnings. But the fact remains that life here on Earth might have a lot in common with life elsewhere. The differences, I have little doubt, will be so great that we can scarcely imagine… But it’s just possible that the similarities might be equally surprising.
To quote directly from the paper:
Our results also indicate that a certain degree of universality would be expected in the types of organic molecules seen on other earth-like planets. Should life exist elsewhere, it would not be surprising if it used at least some of the same amino acids we do. Simple sugars, lipids and nucleobases might also be shared.
…the combined actions of thermodynamics and subsequent natural selection suggest that the genetic code we observe on the Earth today may have significant features in common with life throughout the cosmos.
Paul G. Higgs, Ralph E. Pudritz (2009). A thermodynamic basis for prebiotic amino acid synthesis and the nature of the first genetic code. Astrobiology (accepted) arXiv: 0904.0402