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Life doesn't need water. In fact, all kinds of weird liquids could be solvents for life like water is here on Earth. Scientists say the list of alien water-substitutes is long, from frigid nitrogen to supercritical CO2 to methane to formamide. Whatever inhabits these other liquids would have to take on some truly odd forms, right down to DNA like we've never seen before.
At the Astrobiology Science Conference 2008 that wrapped up yesterday, chemist Steve Benner proposed that formamide might make a great solvent for life with some bizarre biochemistry that mimics our DNA, but in a way we can only imagine. Benner's a great speaker and scientist, but has a tendency to lapse into flights of chemical minutia, so I'll take a page from a New Scientist feature in June that aptly sums up the point:
A suitable solvent is only part of the story of life, of course. Apart from a few viruses, all life on Earth uses deoxyribonucleic acids (DNA) to encode the information needed to build and run an organism. But is there an alternative? Could genetic information be stored another way?Spearheaded by Paul Davies of the BEYOND Institute, several talks at the conference featured ideas about weird life. It appears to be gaining a serious head of steam among scientists, and Davies told me that we might even try looking for these strange creatures on Earth, as part of an alternate-chemistry "shadow ecosystem."DNA consists of a double helix, like a twisted ladder. Every rung of the ladder comprises a pair of molecules called bases. These bases are the part of DNA that actually encode the genes. There are four types, known by the initials G, A, C and T, and they form the alphabet of every genetic code. The struts of the ladder consist of deoxyribose sugars linked by charged phosphate groups.
Biologists have methodically altered different parts of the DNA molecule to explore which aspects of its structure are necessary for it to function properly. They have identified several parts that can be changed without disrupting the molecule. For example, you can replace deoxyribose with another sugar, such as threose. Different and more molecules can be used to represent the bases too.
DNA disasterBut that's where the known options end, says Steven Benner, a synthetic biologist at the Foundation for Applied Molecular Evolution in Gainesville, Florida. Benner has found that replacing the phosphate groups with uncharged substitutes brings disaster. The DNA strand becomes unstable, collapses into a ball and sinks to the bottom of his experimental solution like dregs in a beer keg.
Before these experiments, people wondered why the phosphates were there - whether they were simply a redundant evolutionary artefact, rather like a male nipple. It's now clear that they serve a vital function. The charges keep DNA stiff by organising a cradle of water molecules along its chain; without them, DNA easily wads into a ball - another demonstration of how water is integral to life as we know it. An alien's DNA equivalent in ammonia or methane, say, would therefore need some very different structures to avoid rolling up. Those charged phosphates might have to be replaced by something greasier, like hydrocarbon or benzene molecules, says Jack Szostak, a molecular biologist at Harvard University.
Source: original reporting, New Scientist (sub required)
Image: ufocasebook.com
Comments
Okay, mind officially blown.
ThankyouThankyouThankyouThankyou.
I'm gonna study up on this. I like the idea of aliens coming from a wide range of physical and mental possibilities.
One thing that a friend of mine pointed out, the key to life isn't simply the right chemicals, but the moon was astoundingly beneficial in that it provided a tide, and tide pools. Little pockets that were both water and land and a tiny, stable environment for some form of life to develop.
Without those, I'm not sure how any environment would be stable enough for long enough for the right type of goo to get together and create life.
@aspiringexpatriate:
But wouldn't the bottom of the ocean generally be stable?
And is stability that important for forming life? Just look to the organisms that live in the hot chemical geysers in the ocean. I would doubt they started life in a tide pool and found their way to a hot chemical bath and survived to evolve.
@smcallah: Yes, but in order to become more complex organisms, doesn't it make sense that tide pools would help?
The speculations are assuming an alien would actually carry some form of DNA-analogue in its body, of course - 'prions' are the hypothetical transmissible agents that may be responsible for diseases like scrapie. They don't carry any DNA, yet reproduce. The problem is whether or not when we encounter alien life, that we recognise it as 'life'. It might so offend our anthropocentric (earth-centric?) ideas of life we might refuse to recognise it as such.
Anyone interested in this subject really, really needs to read 'What Does A Martian Look Like? The Science of Extraterrestrial Life' by Ian Stewart and Jack Cohen, respectively a mathematician and a reproductive biologist.
"Before these experiments, people wondered why the phosphates were there - whether they were simply a redundant evolutionary artefact, rather like a male nipple. It's now clear that they serve a vital function. The charges keep DNA stiff by organising a cradle of water molecules along its chain; without them, DNA easily wads into a ball - another demonstration of how water is integral to life as we know it."
As far as I remember, Watson and Crick suggested this and you get that explanation about the role of phosphates in basic lessons of Biochemistry.
Hey, who doesn't like chemical minutia! It's usually just actual chemistry , which for some reason is considered "not-understandeble" by non-chemist, but I digress.
But anything that has to do with "alien"-biochemistry is instantly very cool. There are groups of biologist hunting for earth-aliens, but I imagine that it's hard work as most of our molecular-biology/biochemistry techniques are based on our kond of chemistry and wont work at all with alien"DNA". Which makes the potential discoveries of such ridiculously interesting and exciting.
But as of how dna equivalent molecules might look like in an formamide or methane world is anybodys guess. Especially since we only have one kind of life to base our guesses on.
So come on and find aliens already!
One just has look at our own planet at how life can exist and grow in elements like acids, bases, and neutral substances. I think we're looking for life connected with water because it's the closest thing we know that can support life on a grand scale.
@garygibson: Prions don't actually reproduce themselves, however. From what I understand, they're deformed proteins which have the odd property of, when encountering their undeformed counterparts, pass along their deformation.
It's interesting that we have such a difficult time conceiving of life without DNA. We tend to limit our speculation about possibilities to existing molecule types like nucleic acids. Surely in a non-water solvent another category of large, "organic" information-containing molecule could develop!
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