Non-Carbon Species: Will We Fail to Detect Extra-terrestrial Life? A Galaxy Classic

Carbon is great molecular glue—there’s not doubt about it. Just add water and you’ve got life. Well, maybe it’s not quite that simple, but carbon and water do seem to be a winning combo, at least on planet Earth. That may be why we’ve been limiting ourselves in our search for . The carbon/water combo has worked so well for our own conditions, that we simply can’t imagine anything else supporting life.

Currently, our search for extra-terrestrial life forms has been focused on planets similar to ours. The perplexing idea exists, however, that what would be death to us on Earth, may be life to other beings. What we’re looking for may not lie in our version of the “sweet spot”.

It is definitely worth considering that other options do exist besides water and carbon. Alternative biochemists speculate that there are several atoms and solvents that could potentially spawn life. It is also worth considering that because humans are carbon-based beings, who do their lab work under conditions on planet Earth, we may be a bit biased towards carbon thinking.

Not everyone is a “carbon chauvinist”, however. So far, scientists have already hypothesized several interesting alternatives to carbon. Various elements become more stable and capable of forming complex molecules when under strange (from a human perspective) thermal and atmospheric conditions. For example, silicone-based chemicals would be more stable than equivalent hydrocarbons in a sulphuric-acid-rich setting, which has been noted in some extraterrestrial environments.

Even counter-intuitive elements such as arsenic may be capable of supporting life under the right conditions. Even on Earth some marine algae incorporate arsenic into complex organic molecules such as arsenosugars and arsenobetaines. Several other small life forms use arsenic to generate energy and facilitate growth. Chlorine and sulfur are also possible elemental replacements for carbon. Sulfur is capably of forming long-chain molecules like carbon. Some terrestrial bacteria have already been discovered to survive on sulfur rather than oxygen, by reducing sulfur to hydrogen sulfide.

Nitrogen and phosphorus could also potentially form biochemical molecules. Phosphorus is similar to carbon in that it can form long chain molecules on its own, which would conceivably allow for formation of complex macromolecules. When combined with nitrogen, it can create quite a wide range of molecules, including rings.

So what about water? Isn’t at least water essential to life? Not necessarily. Ammonia, for example, has many of the same properties as water. An ammonia or ammonia-water mixture, stays liquid at much colder temperatures than plain water. Such biochemistries may exist outside the conventional water-based "habitability zone". One exciting example of such a location would be Saturn's largest moon Titan.

Hydrogen fluoride methanol, hydrogen sulfide, hydrogen chloride, and formamide have all been suggested as suitable solvents that could theoretically support alternative biochemistry. All of these “water replacements” have pros and cons when considered in our terrestrial environment. What needs to be considered is that with a radically different environment, comes radically different reactions. Water and carbon might be the very last things capable of supporting life in some extreme planetary conditions. In any case, it is not beyond the realm of feasibility that our first encounter with extra-terrestrial life will not be a solely carbon-based occasion.

Posted by Rebecca Sato.

Links:

New Scientist
Alternative Biochemistry

Comments

[nepharous]

Finding life that is not carbon based may be the way to go. If we find microbial life on Mars and it's it's carbon based then we have a larger question. Is it a lifeform that hitched a ride on one of our crafts or is it a indiginous lifeform? Wherever we go we need to keep in mind that we could pollute the environment with our little bugs from Terra. I guess we better program our machines to check DNA on the spot and hope for the best.
Happy Landings.

[Question Authority]

Hi Nepharous,

One way to check on the origin of any newly-discovered Martian life is to see if it uses DNA or RNA. If it doesn't, we have a winner!

If it does, we have to seriously consider terrestrial contamination as a source. However, with the known Martian environment of high-UV and perchlorate-saturated soil, contamination would probably have come on the lander that detects it. That might make it fairly easy to discount as Martian life.

[jer35mx]

Mars is the nearest planet to here, one question is why do we want to go there?. If anybody finds life and I think the most are like the answers here there is no way we will go there and, if the way is found, use the resources or terraform.

[EvilCosmicMonkey From Knoxville]

It would be interesting to see such an ecosphere, & the beings / life - forms it would support. But probably NOT SO PLEASANT for humans to experience. We need to look on Titan or Europa, but 1st we have to have an idea of what to look for.

[gino]

there is hard evidence that aliens do exist and have been visiting earth for years. look up dr. steven greer at disclosureproject & csetiproject.

there has been a massive govt coverup for 60 years now. all the evidence is there, you just have to read it.

[Ed]

In response to what was said above regarding life living in hostile environments on Earth, I'd just like to say yes, that's true, but it didn't START there - life developed in the sunlight/carbon dioxide rich oceans of millions of years ago, and then evolved further when the atmosphere grew oxygen-rich. The life that lives in hostile environments (for example on the sea bed) only got there because it evolved from life that sprung up in more friendly environments.

[al florea]

iam interested in all types of life forms especially the zeta reticcula

[Elliot Godines]

I agree time can be a factor such as breeding and the time it takes for certain species to reproduce and give birth to their offspring