A principle of quantum theory is that everything that can happen, does.
Happily for the shadow biosphere, it appears that there are bacteria that can incorporate arsenic into their DNA, if required. Arsenic doesn’t appear in anyone’s genetic structure, normally. But if it can happen, it will happen.
The fact that living things can replace one essential element with another means that they also probably do, which means that life is possible in far more places than we ever imagined. There could be life on a moon of Saturn that uses silicon instead of carbon, or selenium instead of sulfur. There could be a shadow ecosystem of microbes made of arsenic living unnoticed under our feet. And if so, and life evolved twice independently on Earth, it’s more than twice as likely that life has evolved on other planets, ending the supposed exceptionalism of our lonely space rock and suggesting that that we have interstellar neighbors.
In fact it seems unlikely that there aren’t alternative ecologies on this planet. Almost all life on earth is microbial, and we know about only a minute proportion of them. Isn’t it more likely than not that they exist in ways we can’t imagine? What this shows is that “what we think are fixed constants of life are not.” Arsenic-based bacteria forces us to think about the possible and atypical not the probable and normal – and suggests the perversely uninhabitable conditions on earth that might have existed when life began. Such as naturally toxic environments like Mono Lake (pictured).
This is a long but very entertaining piece (as is the whole blog) and well worth reading in full.
Continuing the theme of ‘How can we find shadow biosphere lifeforms if we don’t know what to look for?’
Everything we think we know about physics is a theory. And theories are replaced with better theories over time. The theory that all life on earth is carbon-based is a reasonable one, given the visible evidence. Just because we don’t know what non-carbon-based life looks like, it doesn’t mean it’s not there. The comparison with Dark Energy and strange behaviour of subatomic matter is apt – theses are theories derived by inference not observation. The shadow biosphere requires quantum thought.
The possibility of strange forms of alien life seems to have just got a whole lot closer to home. Astrobiologists from Arizona State University, Florida, UC Boulder, NASA, Harvard and Australia have recently theorized about a “shadow biosphere” – a biosphere within a biosphere where alternative biochemistry may be thriving in a way that we haven’t yet thought to examine. Such “weird life” may have had, for hundreds of millions of years, their own ecologies right here in our own backyard. Indeed, like Dark Energy and neutrinos, “weird life” may be all around us even now, only in a non-obvious way. Some astrobiologists are now suggesting that “weird life” is just as likely to be found here on Earth as it is in the Martian regolith, the seas of Europa , or certainly the complex bio-hadronistry on the surface of a neutron star.
In an astrobiology related Nature commentary article titled, “Where are the dolphins?” scientists Jack Cohen and Ian Stewart realized (and showed mathematically that it’s already happening here on Earth) that as a civilization advances they begin to use the available electromagnetic spectrum for communication more fully and efficiently until ultimately their radiative emissions are indistinguishable from blackbody radiation. In other words, when we look out into space with telescopes to search for signs of alien life we will likely mistake it for being just a regular old hot rock. Unless we know how to interpret the signs of such life, we may not be able to distinguish it from the natural background.
If you go looking for known life, you are unlikely to find unknown life…
Biologists are convinced that all known species belong to the same tree of life, and share a common origin. But almost all life on Earth is microbial, and only a tiny fraction of microbes have been characterized, let alone sequenced and positioned on the universal tree. You can’t tell by looking what makes a microbe tick; you have to study its innards. Microbiologists do that using techniques carefully customized to life as we know it. Their methods wouldn’t work for an alternative form of life. If you go looking for known life, you are unlikely to find unknown life.
I believe there is a strong likelihood that Earth possesses a shadow biosphere of alternative microbial life representing the evolutionary products of a second genesis. Maybe also a third, fourth… I also think we might very well discover this shadow biosphere soon. It could be ecologically separate, confined to niches beyond the reach of known life by virtue of extreme heat, cold, acidity or other variables. Or it could interpenetrate the known biosphere in both physical and parameter space. There could be, in effect, alien microbes right under our noses (or even in our noses). Chances are, we would not yet be aware of the fact, especially if the weird shadow life is present at relatively low abundance. But a targeted search for weird microbes, and the weird viruses that prey on them, could find shadow life any day soon.
Prof. Paul Davies | http://edge.org/response-detail/10860