Too Salty
by MikeGeneA new analysis of the Martian rock that gave hints of water on the Red Planet — and, therefore, optimism about the prospect of life — now suggests the water was more likely a thick brine, far too salty to support life as we know it.The finding, by scientists at Harvard University and Stony Brook University, is detailed this week in the journal Science.
"Liquid water is required by all species on Earth and we've assumed that water is the very least that would be necessary for life on Mars," says Nicholas J. Tosca, a postdoctoral researcher in Harvard's Department of Organismic and Evolutionary Biology. "However, to really assess Mars' habitability we need to consider the properties of its water. Not all of Earth's waters are able to support life, and the limits of terrestrial life are sharply defined by water's temperature, acidity, and salinity."
["¦.]
The water activity of pure water is 1.0, where all of its molecules are unaffected by dissolved solute and free to mediate biological processes. Terrestrial seawater has a water activity of 0.98. Decades of research, largely from the food industry, have shown that few known organisms can grow when water activity falls below 0.9, and very few can survive below 0.85.
Based on the chemical composition of salts that precipitated out of ancient Martian waters, Tosca and his colleagues project that the water activity of Martian water was at most 0.78 to 0.86, and quite possibly reaching below 0.5 as evaporation continued to concentrate the brines, making it an environment uninhabitable by terrestrial species.
"This doesn't rule out life forms of a type we've never encountered," Knoll says, "but life that could originate and persist in such a salty setting would require biochemistry distinct from any known among even the most robust halophiles on Earth."
The scientists say that the handful of terrestrial halophiles — species that can tolerate high salinity — descended from ancestors that first evolved in purer waters. Based on what we know about Earth, they say that it's difficult to imagine life arising in acidic, oxidizing brines like those inferred for ancient Mars.
-Here
June 2nd, 2008 at 1:33 am
Look, clearly the existence of life on Mars indicates that there's no design in the universe. What kind of designer would bother with such on a planet where it has no hope of developing into more complicated l…
Oh wait. Life wasn't found?
*ahem* I meant… Look, clearly the lack of life on Mars indicates that there's no design in the universe. What kind of designer would bother with planets that are dead and devoid of life for so long?
Comment by nullasalus — June 2, 2008 @ 1:33 am
June 2nd, 2008 at 4:36 pm
Leaving the sarcasm aside, if possible, what does this tell us about the origins argument? Anything?
Comment by The Pixie — June 2, 2008 @ 4:36 pm
June 2nd, 2008 at 10:42 pm
Hi Pixie,
I'm not sure it tells us anything. I found it interesting because it may be raising another "specification" for abiogenesis; the mere existence of water is not sufficient.
It would seem to me that those who think abiogenesis is some type of emergent, law-like process should be at least a little concerned in such an Earth-like planet as Mars has always been devoid of endogenous life.
Comment by MikeGene — June 2, 2008 @ 10:42 pm
June 3rd, 2008 at 1:44 am
The Pixie,
Guillermo Gonzalez mentions that while extremophiles can exist in some extremely salty conditions, they are less able to survive a 'wider range' of conditions. In other words, they are specialists - less able to exploit changing conditions, therefore less likely to survive deep time or catastrophic events.
One might consider this article as supporting the Priveleged Planet argument. That is, if one was tenured.
Oops. Sarcasm. Sorry.
Comment by chunkdz — June 3, 2008 @ 1:44 am
June 3rd, 2008 at 3:26 am
Hi Mike, I should have been explicit, sorry - my coment was directed at null who seemed to be trying to score points.
I agree it is interesting, but I disagree that it raises another specification. I think you have it the wrong way around. The specification (too much salt will prevent abiogenesis) was already known, and they have applied that specification to the new data. They are not saying there is no life, therefore too much salt is a problem; rather they are saying there is too much salt (i.e., it is not so Earth-like afterall), therefore we would not expect life.
Comment by The Pixie — June 3, 2008 @ 3:26 am
June 3rd, 2008 at 10:47 am
Pixie
That's how I read that, too.
Comment by DonaldM — June 3, 2008 @ 10:47 am
June 3rd, 2008 at 11:27 am
The Pixie,
LOL!:lol:
Comment by chunkdz — June 3, 2008 @ 11:27 am
June 3rd, 2008 at 11:27 am
They are saying "water isn't a sufficient indicator - it might be too salty."
Comment by Pez — June 3, 2008 @ 11:27 am
June 3rd, 2008 at 12:55 pm
chunkdz
Insightful and hilarious too - incredible.
Oops, now I am being sarcastic. Well me try again. Why not actually make a contribution, instead of content-free ridicule, chunkdz?
Pez
… And now the signs are that Martian water was too salty, they therefore think life was unlikely there.
They are not saying: They have found there was never any life on Mars, and the signs indicate the water was too salt; therefore they have changed the specification for abiogenesis.
Comment by The Pixie — June 3, 2008 @ 12:55 pm
June 3rd, 2008 at 1:12 pm
Pixie,
I did.
Sorry for laughing at you.
Comment by chunkdz — June 3, 2008 @ 1:12 pm
June 3rd, 2008 at 1:17 pm
This is only one rock that is now indicating that if there was water present, the water would have had high levels of salt.
My question is: how do we know if this rock (or whatever rocks we do have) is indicative of all potential water that may have existed on Mars?
A sample of the earth from the Dead Sea and a sample of the earth from the Great Lakes may paint vastly different pictures of what the earth was like - from the vantage of extra-terrestrials that somehow came in contact with one or the other samples.
Comment by Doug — June 3, 2008 @ 1:17 pm
June 3rd, 2008 at 1:48 pm
From the article,
Some quick googling found that haloarchaea can exist in nearly saturated salt solution, which has a .75 water activity. Most fungi live at nearly .70 water activity. Seems that before the great martian evaporation, life was certainly possible based on these parameters.
As for the Harvard studies' assertion that life could not originate in such a salty setting, how can anyone make such an assertion about a completely unknown phenomenon? To say that too much salt will prevent abiogenesis is an assertion that falls into that category of "not even wrong".
Comment by chunkdz — June 3, 2008 @ 1:48 pm
June 3rd, 2008 at 3:59 pm
chunkdz
Yeah, you made a comment. Then I made a comment, and you responded with content-free ridicule. Or am I missing something here? Does making one substantive post give you a free pass for the rest of the thread? I suppose it is too much to hope that you would want to explain why you were laughing at me? I would much prefer an explanation to an apology.
They do not:
Comment by The Pixie — June 3, 2008 @ 3:59 pm
June 3rd, 2008 at 4:58 pm
The Pixie,
I'm sorry if I hurt you.
It struck me that you couldn't possibly "know" how much salt can be present for abiogenesis to occur or not occur. The self-assuredness with which you spoke was funny at the time, but now that I have seen the damage that I have done, it's not funny anymore. I deeply regret my actions.
How does throwing out a disclaimer about one unknown help their assertion about another unknown?
At any rate, Tosca's conclusion is confusing. They estimated .78-.86 aw for Mars' water, and as I pointed out most fungi live happily at .70 aw. So why did they decide that life that formed at .78-.86 aw would have had some unknown biochemical makeup?
And who's to say high salinity isn't useful for abiogenesis? Who's to say anything about an imagined event, much less claim to know about it's salinity threshold?
Comment by chunkdz — June 3, 2008 @ 4:58 pm
June 3rd, 2008 at 5:31 pm
As was stated in the article they were assuming life similar to that on Earth and life on Earth as we see today adapted to live in those environments. So the assumption was Martian life would also need to start in more favorable water and adapt in the same way. This is an example of scientists having to make very precise statements when forming a hypothesis, they started with the assumption that they are looking for life with a basic chemistry similar to life on Earth. They have gathered evidence that makes that hypothesis seem likely to be wrong. This doesn't say anything about some totally different form of life, but we cannot make a meaningful hypothesis about a complete unknown. Also I don't think this says anything at all about where life on Earth might have originally formed; its possible original Earth life required high salt levels, we simply don't have any evidence (that I'm aware of) to suggest that.
Comment by Todd Berkebile — June 3, 2008 @ 5:31 pm
June 3rd, 2008 at 5:55 pm
Thanks Todd, for a reply brimming with insight. However, I feel compelled to point out that fungi live happily at .70 aw, therefore I see no reason to assume that Martian life would require a unique unknown biochemical makeup, given the much more favorable conditions (.78 to .86 aw) on Mars.
What kind of water did terrestrial life start in?
Comment by chunkdz — June 3, 2008 @ 5:55 pm
June 3rd, 2008 at 6:55 pm
chuckdz
See, was that so very hard? And now you have explained, that allows me to actually defend myself. Of course I have no idea how much salt can be present for abiogenesis. My point was that the specification already existed, that it had not be changed.
They say that Earth-like life could not appear in high salt water, given that Earth-like life on Earth cannot survive in high salt water. They then say that non-Earth-like life might. Seems a reasonable position to me.
Then I suggest you e-mail them and ask them. You may well have a point. I find it odd that 0.7 is a saturated solution; how can there be more salt than that? What articles did you find about salt-loving fungi? A link might be helpful to support your case.
Comment by The Pixie — June 3, 2008 @ 6:55 pm
June 4th, 2008 at 11:20 am
Pixie
Right.
You specified "too much salt will prevent abiogenesis". How can you possibly know this?
Earth-like life does exist in highly saline water. I pointed this out already. Google haloarchaea - they're very "earth-like" - they have DNA and everything.
Who told you that?
I never mentioned salt loving fungi. I mentioned fungi that thrive at relatively low water activity levels.
Here's some that propogate at a measly .61 aw, well below the proposed activity of Martian water.
Comment by chunkdz — June 4, 2008 @ 11:20 am
June 4th, 2008 at 4:22 pm
chunkdz
That is what the article says. I was paraphrasing the article.
Not sure where I found it originally, but this page (same site as yours coincidentally) gives a figure of 0.752 for the activity of water saturated with salt.
Sorry, I should have said salt tolerant fungi. By the way, you said "Most fungi live at nearly .70 water activity." I am still wondering why you think most fungi live at 0.7. Do you have a link for that?
Have you pointed out to the authors that they are wrong? I would be interested to hear their response.
Comment by The Pixie — June 4, 2008 @ 4:22 pm