Last night, my wife and I had dinner with a friend of ours from the Szostak Lab (yes at Buddha's Delight - I had the "beef" taro stirfry).
There we discussed Capote (we just saw the movie) and the existence of ribose in a pre-biotic earth. Apparently it is unlikely that sugars, such as ribose, would have been in high concentrations in the hypothetical chemistry of primitive earth (see her PNAS paper). Although sugars are easily generated (spontaneously from formaldehyde), they decay very rapidly - thus at steady state it's likely that there wasn't much sugar around. Sugars form the backbone for molecules such as RNA and DNA.
No sugars, no ribose based nucleic acids.
Thus a self-replicating molecule would probably require a different backbone, perhaps one composed of polypeptides. Such peptide nucleic acids (or PNAs) have been synthesized in labs and have interesting properties, such as the ability to hybridize with single stranded DNA.
So this morning I got up with thoughts of tofu beef, effeminate NY intellectuals, and the origin of life, swimming through my head ... as I opened up the paper and read, Saturn Moon Has Geysers, Hinting Life Is a Possibility.
(Image from NASA - for more see the special edition of Science Magazine by following this link.)
So Cassini found evidence of liquid water on Enceladus ... very interesting. Then (in the NY Times article) I read this sentence:
Life requires at least three ingredients -- water, heat and carbon-based molecules
No no no. You don't know that life requires water! This is a good example of pretending to know more than we do. Perhaps life can arise in another medium - how do we know? For a complete discussion on this topic, I have an old post discussing the relationship between life and water.
My point. Compare this rash absolutist idea (life NEEDS water), to a careful study with a conclusion (in the probable chemistry of pre-biotic earth, self-replicating molecules MOST LIKELY did not contain sugars). These are examples of bad and good reasoning with regards to the origin of life.
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I agree with your posting. We think we know more then we do. It would be interesting to see if there is biotic life under those hot pockets. Based on what we know, there could be some animal forms that are thermo tolerant that could survive in these kinds of conditions.
You've got a good point - the conditions through which life can and cannot form and the ingredients that are required will remain unclear until we can at least find and study one instance of extraterrestrial life. Consequently, it is a bit shortsighted to plainly state that life requires liquid water. But it's certainly not "rash" - there are excellent and logical reasons for the belief.
Liquid seems by far essential for life (as we know it!), because of its stability, Brownian motion, etc... Liquid water is by far the best medium we know of for carbon-based life to develop. And carbon-based life appears to be by far the most likely form, because of the unique nature of carbon and the mind-boggling number of compounds it allows. There is a chain of reasoning that supports these ideas, which time and space preclude me listing here, and each link in the chain is strong.
Yes, there is a possibility that life could perhaps also form without the presence of liquid water. As I understand it, liquid ammonia might be suitable. Of course, one major problem with a liquid ammonia environment is how cold it is: chemical reactions are much slower at these temperatures, which slams the brakes on the development of life and its propagation. I recall reading somewhere that one obstacle for liquid ammonia life is that any hypothetical planet's star could feasibly go through it's entire lifecycle and be extinguished before anything as complicated as single-celled organisms could manifest themselves. Again, we just don't know.
Pouncing on the New York Times for saying life requires water reminds me of people who insist on the usage of "he or she"/"his or hers" instead of "they"/"theirs." Sure, these people are technically correct, but the construction they insist be used is also less convenient and a bit clunky.
We must find examples of extraterrestrial life if we are ever to answer these questions. Is it better to look at worlds and places where liquid water can and does exist, or in the interest of being fair and balanced, should we also spend our resources sending probes and focusing our scopes on a much wider range of environments?
I'd argue we should operate under the assumption that life needs water until proven otherwise, because water appears to be ideal for the development and propagation of complex organic molecules in ways that allow living organisms to emerge. It's the pragmatic approach.
Sorry if this is a repost from an earlier thread.
So the Szostak lab had a nice paper some time ago describing that EtOH concentrations up to 10% stabilized aptamers and allowed a particular RNA to bind its ligand with higher affinity. The line of research has essentially been dropped to my knowledge but to me it speaks of the likelihood that the precursor to RNA would/could have likely had to function in a variety of conditions including non-aqueous solutions.
A procedural artifact during an in vitro selection in a previous lab led to an organophilic ribozyme. The RNA functioned in a variety of organic solutions of up to 80% with cleavage rates of 1/min. The postdoc who did the work was gearing it towards an origin of life angle.
Sorry if my post sounds harsh ... must have been the lack of coffee ... in anycase I'm not pouncing on the NY Times -or didn't intend to ... I just that I've gone through this argument with many people.
I agree that liquids would help, but that it has to be water I don't agree. In fact water may turn out to be bad for kick starting life. Water is highly reactive, preventing large molecules from assembling. In the lab most organic synthesis reactions take place in some unreactive environment (like DMSO - that would be cool and unlikely an ocean of DMSO!)
In fact there many in the exobiology field who think that water is not necessary at all and that other liquids would be preferable ... let alone that it is necessary.
I hadn't read your earlier post re: water and life before I commented, but I went back and perused it. The idea that non-aqueous solutions might be ideal for the emergence of life is plausible and interesting - do you have any suggestions for further reading on this?
I admit, I'm one of those starry-eyed dreamers that hopes we'll someday find life in liquid methane or liquid ammonia, but again the biggest obstacle that I see to this is the very slow speed of reactions in these very very cold substances.
I still think seeking liquid water is the best option for finding extraterrestrial life. Or maybe we should start looking for those DMSO oceans. :)
I agree with your earlier post that the key step in getting life going is the first one of a self-replication molecule of some kind (certainly not a nucleic acid). Also, that a liquid phase seems most likely rather than a solid or gas. Another exotic liquid that might be considered is supercritical CO2, but that would require CO2 under considerable pressure (don't know if pools of SC CO2 is consistent with a highy reducing environment).
Some stated disadvantages of water (reactivity) are also key to its advantages: good acid/base catalyst, extensive H-bonded array facilitating proton transfer reactions. It's a trade-off coming down to relative kinetics of good vs. bad stuff happening. Possibly some kind of compartmentation, such as the NASA picture suggests. Ammonia shares some of the prototropic properties of water, and could be kept liquid at higher temperatures in a pressurized environment, but I don't see any advantage in bringing it into a theoretical argument.
Methane is a lousy catalyst and would be really poor solvent in a largely inorganic world, as well as low BP. But I wonder about methane hydrates, which can exist under moderate T and P. I don't know enough about them, but they might offer some of the best of both "worlds." In all, I'm inclined to vote for water as major player.
O/T, but on the they vs. he/she usage. I guess my HS English teacher drilled it deeply into my head that a singular subject takes a singular predicate, and likewise for the plurals. I still subconciously parse every sentence I read, and that's a challenge when "they" wanders back and forth between singular and plural in the same sentence. I'm also one of the dinosaurs who still regard data, media, bacteria, etc. as plural nouns (or maybe it was my Latin teacher). As is well known, progress occurs one funeral at a time...
"No no no. You don't know that life requires water!"
I would like to add that we also don't know if life has evolved elsewhere using Silicon as a building block versus Carbon.
There is so much that we do not know about life!
I agree! (I was waiting for someone to point this out.)
Yes. In fact just last night I had another conversation with our friend from the Szostak Lab about the whole water & life business. She made a similar arguement - to synthesize organic compounds from inorganic molecules, water would help a great deal. Having said that compartmentalization (some reactions in water, some in a seperate phase), as you've pointed out, is possible. In addition once you do have some organic compounds, or an organic solvent such as ethanol or something exotic such as DMSO, then perhaps life could start in a non-aqueous environment.
"I would like to add that we also don't know if life has evolved elsewhere using Silicon as a building block versus Carbon."
It's my understanding, and since I'm lazy I won't dig for the refs, that there was a considerable attempt to synthesize DNA nucleobases from silicon and it was too unstable to yield an appreciable product. Doesn't mean though that a vastly different environment wouldn't favor the reaction.