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Water Not a Good Enough Guide To Find Alien Life
An anonymous reader noted an article in Cosmos that questions the conventional wisdom of the "follow the water" strategy of seeking extraterrestrial life, saying "There's an awful lot of places where water could exist — either on the surface of the Earth, or deep within it — yet life is largely concentrated in a small sliver of this."
Everywhere on Earth we find water, we find life.
The argument seems to be that for your statement, everywhere on Earth's surface is true. However, for everywhere above or below Earth's surface your statement does not hold.
He's an idiot.
Not quite an idiot but certainly shortsighted. The real confusing thing for me is that his "sliver" -- 12% -- would still be scientifically revolutionary if we hit up a planet and 12% of the water on it contained life. Can he produce any other chemical or indicator we can detect light years away that produces some percentage greater than that for supporting life? He can't, that's why the article wraps up with water still being our best guess and no recommendations to change anything.
My work here is dung.
It's not clear what Lineweaver is trying to say, here. Even when I took graduate astrobiology nearly 10 years ago, we were taught that you needed three things for life: raw elements (CHON, in particular), water, and an energy source. From the article, it sounds like he thinks he's had this revelatory notion just now.
Of the three ingredients, water does seem to be the hardest to find in sufficient abundance for a good likelihood of life arising anywhere. There are certain the raw materials and often energy sources available in many places, but water seems to be the missing factor in most of the solar system. So it's not a sufficient condition, it does seem like the smart thing to look for first.
(Also, his 12% figure confuses me. Is he including the entire mantle, for example? Because there isn't a lot of water there, as I recall, so you wouldn't expect to find a lot of life there. That alone would pretty easily throw the calculation in favor of his result. However, we have found life in deep rocks under the Earth, which is still pretty amazing and suggests that it's danged hardy.)
Nobody is saying there can't be life without water.
They're saying that since we have no idea of what it would look like, or how to look for it, there is simply no point in trying to look for it.
Tell me, how would you undertake to look for the conditions of life that we don't even have any clue as to how it works chemically? At which point, you could look at any environment and say "well, we can't rule out life there" -- which basically serves no purpose. That doesn't narrow your search in any meaningful way.
We have no ability to posit a theory, test it, or look for it when water isn't involved. At least by sticking with water within a range similar to that of Earth, we can intelligently say "well, we have life that lives in 150C, that place could as well".
There really isn't any way we can look in places that are outside what we can understand. From a science perspective, that's just simply a dead-end at present.
Lost at C:>. Found at C.
If life is just an evolved entity composed of randomly assembled machines, as some biologists claim, then it begs the question of wether or not there might be 'life' out there that is not water based, but based on say, sand -- or silicon.
That is not what "begs the question" means.
http://begthequestion.info/
If Slashdot were chemistry it would look like this:Cadaverine
Looking up some of the author's actual publications on this issue shows some very interesting details that greatly modify this picture. See: http://www.mso.anu.edu.au/~charley/papers/Jones&LineweaverProceedingsv7color.pdf.
Most remarkably he calculates that 99% of the Earth's ACTUAL liquid water contains life!!
This 12% business is the volume of the Earth where liquid water can physically exist due to its pressure-temperature phase diagram - whether or not there is actually much (or any water) there.
There are yet more limitations on this claim: it is based on the presumption that there is no life below 5 km in the Earth's crust. This is a region very slightly explored, so it can hardly be said that this claim is based on extensive direct observation. The assumption is really that the temperatures below this depth are too high life to exist (the assumed limit is 150 C). But organisms known to survive this temperature dormantly (tardigrades) are actually complex organisms (not simple extremophiles), and it was only recently that organisms were discovered that actually thrive above 121 C (the temperature of an autoclave), so the assumption that this is really the upper limit seems weak.
And the claims get even weaker. Why have we only recently discovered thermophiles above 121 C? Because there are very few accessible locations where liquid water can exist above this temp in which to observe it! Concentrated salts can raise boiling points only so far, beyond which only considerable pressure will keep it liquid. Probably the only environments we can access currently to investigate the >150 C regime are the black smoker vents on the sea floor, where emerging water hits 400 C (before rapidly cooling due to mixing).
And by this same token, the high pressure high temperature liquid water regime will be impossible for astronomers to directly observe anyway (its buried under kilometers of rock, or deep, dense atmospheres, don't ya know).
So if it is an environment where we can actually hope to OBSERVE liquid water (rather than simply postulate its existence) then yes indeed, it is almost certain to be one where life-as-we-know-it can exist.
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Silicon doesn't have much in the way of properties that would promote life. It's a nice sci-fi treatment, from maybe the 50's, but it's not realistic chemically for exactly the reason you mentioned. Silicon readily forms a single type of crystal with itself; carbon readily forms millions upon millions of different molecules with all sorts of other elements... especially hydrogen, who has a great way of bonding/not really bonding with itself.
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