You specified "too much salt will prevent abiogenesis". How can you possibly know this?

That is what the article says. I was paraphrasing the article.

Who told you that?

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.

I never mentioned salt loving fungi.

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?

Here's some that propogate at a measly .61 aw, well below the proposed activity of Martian water.

Have you pointed out to the authors that they are wrong? I would be interested to hear their response.

Of course I have no idea how much salt can be present for abiogenesis.

Right.

My point was that the specification already existed, that it had not be changed.

You specified "too much salt will prevent abiogenesis". How can you possibly know this?

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.

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.

I find it odd that 0.7 is a saturated solution…

Who told you that?

What articles did you find about salt-loving fungi? A link might be helpful to support your case.

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.

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.

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.

How does throwing out a disclaimer about one unknown help their assertion about another unknown?

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.

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?

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.

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.

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.

So the assumption was Martian life would also need to start in more favorable water…

What kind of water did terrestrial life start in?

chunkdz : 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?

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.

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'm sorry if I hurt you.

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.

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.

They do not:

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?

I did.
Sorry for laughing at you.

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.

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?

They do not:

"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 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."

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".

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.

Why not actually make a contribution, instead of content-free ridicule, chunkdz?

I did.

Sorry for laughing at you.