7 ms·

I know that without water life would have never begun, but I still don't fully understand why it is necessary. It is still big discovery though, if life is that

by eddd 11y ago

I know that without water life would have never begun, but I still don't fully understand why it is necessary. It is still big discovery though, if life is that common I think we should be more careful during migration there, "Marsian" common cold could wipe out the entire human colony.

dangrossman 11y ago
> I know that without water life would have never begun, but I still don't fully understand why it is necessary. "Life" is a bunch of chemical processes. A necessary prerequisite is therefore a solvent in which those chemical processes can occur, and which can move substances around, whether it's within a cell, an organism, or an environment. Of all the potential solvents, solids can't move stuff around, and in gases, only volatile and highly concentrated substances would have a chance to react. It's also too easy to move around in a gas: potential gas-based "life" would just...fall apart. So the solvent and carrier being a liquid is also likely a prerequisite for life. It also has to stay a liquid at a relatively wide range of temperatures, and be abundant enough so that all the rare coincidences that might lead to life have a chance of happening and perpetuating. Water is the only molecule that fits the bill, and happens to be the second most common molecule in the universe.
- eddd 11y ago
  I am not good at chemistry, but liquid methane–ethane wouldn't fit the profile?
  - eddd 11y ago
    Actually I found comprehensive answer here if anyone is interested: http://www.space.com/13639-alien-life-methane-habitable-zone.html http://www.space.com/13639-alien-life-methane-habitable-zone...
    - VLM 11y ago
      It doesn't really say "why". Water ionizes really conveniently so you can make it an acid OR a base (which is sorta unusual and it can talk to acidic or basic things), and is polar (its got a + and a - electrical side, more or less, so it can talk to + or - things), and has hydrogen bonds (so you get liquid lifestyle at gas temps) For one why, look up amphoteric and zwitterion. Water has a super convenient pH range where about a ten millionth of pure water self ionizes aka ten to neg seventh or pH of 7, and all kinds of super convenient reactions occur above and below that pH and its really easy to manipulate ionization rates around that level without using too much. You don't need just a liquid but one where you can really screw around with something like amino acids by easily and cheaply changing the ionization rate of the liquid. So there are super convenient chemical reactions that depend on the ionization level of the liquid and its really easy to manipulate water. Conveniently water "just works" without having to add tons of other stuff to it. Liquid methane isn't polar enough to really be useful when messing with ionic substances (table salt, etc). Whatever you use for a liquid, it needs to be polar so ionic stuff like salts can dissolve. It turns out that interesting chemistry doesn't happen with non-polar substances at normal temps; thats why when you bury stuff for a couple million years the only thing left behind undecayed (more or less) is non-polar hydrocarbons (crude oil). Ammonia is polar but has other issues. The hydrogen bonds are important. Water should be a gas at room temp. Really, it should, looking at bonds and molecular weight and stuff. Yet the hydrogen bonds that form keep it liquid at room temp. So you get "gas speed" chemical reactions at "high" room temperature, yet its liquid to a ridiculously high temp. Maybe some custom liquid silicone with some bolted on weirdness could make a useful artificial blood plasma or "stuff" for life to live in. How it would make it without the chemical plant being made first is mysterious.
      - cLeEOGPw 11y ago
        Sometimes I wonder that not only it is not possible for other forms of life to exist that wouldn't use water, carbon and others, but that we have life just because it so happened coincidentally that our universe were created with the exact properties needed for the laws of physics to support life for a short while in some places.
  - maaku 11y ago
    Those are non-polar, so would not work as a liquid environment for Earth-like biochemistry. Doesn't rule out the possibility of different forms of life ... but there is a high prior against it.
  - logfromblammo 11y ago
    I'd order the candidates for the basis of lifelike chemistry complexes as follows: H2O, NH3, SO2, HCOOH, CH4. A lot of the common molecules aren't good solvents or react too readily with other common elements or molecules, like oxygen or halogens. And molecules that are good solvents just aren't common enough to dissolve much of anything. Methane would probably only work in an oxygen-deficient environment, and ethane wouldn't form enough by coincidence to be a meaningful solvent in comparison to methane or other simple organics. And it just so happens that H2O is very common and a great solvent, so any other potential solvent would probably have a little water in it anyway. And if it's there, a lifelike chemistry complex would probably make use of it in some way.
- comboy 11y ago
  "Water is the only molecule that fits the bill, and happens to be the second most common molecule in the universe." [citation needed]
  - deleted 11y ago
    [deleted]
  - dangrossman 11y ago
    What an annoying meme. What part did you find so surprising that you want additional references, but couldn't find a better way to ask for them? As to the first part, there are uncountable examples of water-based life, and zero examples of non-water-based life. That doesn't rule out its existence, but basic chemistry makes it unlikely, and it won't look anything like life as we know it. No other liquid has the properties needed for any kind of life observed. As to the second: https://www.google.com/search#q=%22second+most+common+molecule+in+the+universe%22 https://www.google.com/search#q=%22second+most+common+molecu...
    - akiselev 11y ago
      He's likely asking for a citation that shows that water is the second most common molecule in the universe, which is a quite a claim to make based on our understanding of astrophysics and astrochemistry. The most common molecule is diatomic hydrogen and the second most common is helium. That'll likely be true for hundreds of billions of years, if not trillions, due to the way stars burn their atomic fuel. Even if you don't include atomic helium as a molecule, the second most prevalent would likely be the most reactive combination of hydrogen and nitrogen/carbon.
      - dangrossman 11y ago
        Atomic helium is not a molecule. Oxygen is significantly more abundant than either nitrogen or carbon in the universe. In the interstellar clouds that give rise to stars, hydrogen runs into a lot more oxygen than carbon or nitrogen, so you're going to end up with more water than any other molecule but hydrogen gas. https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Abundance_of_elements_in_the_Universe https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem... Also see this delightful comment by logfromblammo: https://news.ycombinator.com/item?id=10292067 https://news.ycombinator.com/item?id=10292067
danenania 11y ago
Water is necessary for all "life as we know it". There could be configurations we don't know about that allow life to form from radically different constituents. The universe is big enough to allow for the possibility, but it's so theoretical that we have no framework for understanding how these kinds of exotic lifeforms would work or how to look for evidence of their existence. So while we shouldn't exclude the possibility, "life as we know it" is the most sensible place to start.
maaku 11y ago
Earth life is aquatic. Our chemistry happens immersed in water. When life left the oceans, living beings like you and I took the water with us. We are walking bags of water: approx 75% by weight. Of course martian life could be different than terran life, and that would be interesting too. But there are reasons to suspect that liquid chemical reactions was necessary at the genesis of life, and water is a uniquely optimal liquid for this purpose. A martian virus is unlikely to do anything to your immune system. For one thing it is unlikely that the virus would even use the same genetic codes (A C T G) as terran DNA, unless we share a common ancestor, and even in that case it wouldn't do anything against you & your immune system would eventually create an antibody and wipe it out. We fear things like bird flu and swine flu because they develop in close proximity to humans in analogous systems, honing attack vectors specifically targeting some weakness of the animal body. An alien virus would likewise be good at attacking aliens, not us.
- eddd 11y ago
  I would rather say, that the fear of the unknown is playing major part. Any maybe too much sci-fi movies.
jerf 11y ago
You know that science fiction trope of the deadly planet full of life where every last life form is trying to kill every other life form, and they've evolved a frightful array of offenses and defenses to do it? That planet is Earth. The real Earth. We perceive our ecosystem as friendly only because we've co-evolved with it. It is in objective terms a vicious, vicious place, with every cubic centimeter of any useful resource contended for by thousands or millions of organisms, fighting each other in every conceivable chemical, biological, and physical manner, and in particularly sophisticated corners of the Earth ecosystem, even social manners. It may look peaceful from the apex, but it's not when you get close. The likelihood of some sort of Martian bacteria getting here and causing amazing problems can never quite be eliminated, but it's very, very low. Plus, if Martian life ever existed, it actually won't be entirely disconnected from Earth life due to what you could call "transpermia": http://users.tpg.com.au/users/horsts/swaprock.html http://users.tpg.com.au/users/horsts/swaprock.html In fact if life is discovered on Mars, the next question is whether it is just Earth life that hitched a ride and managed to adapt to conditions that aren't necessarily all that much harsher than conditions we've found life on here on Earth. It's interesting either way, but the implications are hugely different between some hitchhiking Earth life vs. life that clearly came from a different abiogenesis event.

by eddd 11y ago

dangrossman 11y ago

> I know that without water life would have never begun, but I still don't fully understand why it is necessary. "Life" is a bunch of chemical processes. A necessary prerequisite is therefore a solvent in which those chemical processes can occur, and which can move substances around, whether it's within a cell, an organism, or an environment. Of all the potential solvents, solids can't move stuff around, and in gases, only volatile and highly concentrated substances would have a chance to react. It's also too easy to move around in a gas: potential gas-based "life" would just...fall apart. So the solvent and carrier being a liquid is also likely a prerequisite for life. It also has to stay a liquid at a relatively wide range of temperatures, and be abundant enough so that all the rare coincidences that might lead to life have a chance of happening and perpetuating. Water is the only molecule that fits the bill, and happens to be the second most common molecule in the universe.

eddd 11y ago
I am not good at chemistry, but liquid methane–ethane wouldn't fit the profile?
- eddd 11y ago
  Actually I found comprehensive answer here if anyone is interested: http://www.space.com/13639-alien-life-methane-habitable-zone.html http://www.space.com/13639-alien-life-methane-habitable-zone...
  - VLM 11y ago
    It doesn't really say "why". Water ionizes really conveniently so you can make it an acid OR a base (which is sorta unusual and it can talk to acidic or basic things), and is polar (its got a + and a - electrical side, more or less, so it can talk to + or - things), and has hydrogen bonds (so you get liquid lifestyle at gas temps) For one why, look up amphoteric and zwitterion. Water has a super convenient pH range where about a ten millionth of pure water self ionizes aka ten to neg seventh or pH of 7, and all kinds of super convenient reactions occur above and below that pH and its really easy to manipulate ionization rates around that level without using too much. You don't need just a liquid but one where you can really screw around with something like amino acids by easily and cheaply changing the ionization rate of the liquid. So there are super convenient chemical reactions that depend on the ionization level of the liquid and its really easy to manipulate water. Conveniently water "just works" without having to add tons of other stuff to it. Liquid methane isn't polar enough to really be useful when messing with ionic substances (table salt, etc). Whatever you use for a liquid, it needs to be polar so ionic stuff like salts can dissolve. It turns out that interesting chemistry doesn't happen with non-polar substances at normal temps; thats why when you bury stuff for a couple million years the only thing left behind undecayed (more or less) is non-polar hydrocarbons (crude oil). Ammonia is polar but has other issues. The hydrogen bonds are important. Water should be a gas at room temp. Really, it should, looking at bonds and molecular weight and stuff. Yet the hydrogen bonds that form keep it liquid at room temp. So you get "gas speed" chemical reactions at "high" room temperature, yet its liquid to a ridiculously high temp. Maybe some custom liquid silicone with some bolted on weirdness could make a useful artificial blood plasma or "stuff" for life to live in. How it would make it without the chemical plant being made first is mysterious.
    - cLeEOGPw 11y ago
      Sometimes I wonder that not only it is not possible for other forms of life to exist that wouldn't use water, carbon and others, but that we have life just because it so happened coincidentally that our universe were created with the exact properties needed for the laws of physics to support life for a short while in some places.
- maaku 11y ago
  Those are non-polar, so would not work as a liquid environment for Earth-like biochemistry. Doesn't rule out the possibility of different forms of life ... but there is a high prior against it.
- logfromblammo 11y ago
  I'd order the candidates for the basis of lifelike chemistry complexes as follows: H2O, NH3, SO2, HCOOH, CH4. A lot of the common molecules aren't good solvents or react too readily with other common elements or molecules, like oxygen or halogens. And molecules that are good solvents just aren't common enough to dissolve much of anything. Methane would probably only work in an oxygen-deficient environment, and ethane wouldn't form enough by coincidence to be a meaningful solvent in comparison to methane or other simple organics. And it just so happens that H2O is very common and a great solvent, so any other potential solvent would probably have a little water in it anyway. And if it's there, a lifelike chemistry complex would probably make use of it in some way.
comboy 11y ago
"Water is the only molecule that fits the bill, and happens to be the second most common molecule in the universe." [citation needed]
- deleted 11y ago
  [deleted]
- dangrossman 11y ago
  What an annoying meme. What part did you find so surprising that you want additional references, but couldn't find a better way to ask for them? As to the first part, there are uncountable examples of water-based life, and zero examples of non-water-based life. That doesn't rule out its existence, but basic chemistry makes it unlikely, and it won't look anything like life as we know it. No other liquid has the properties needed for any kind of life observed. As to the second: https://www.google.com/search#q=%22second+most+common+molecule+in+the+universe%22 https://www.google.com/search#q=%22second+most+common+molecu...
  - akiselev 11y ago
    He's likely asking for a citation that shows that water is the second most common molecule in the universe, which is a quite a claim to make based on our understanding of astrophysics and astrochemistry. The most common molecule is diatomic hydrogen and the second most common is helium. That'll likely be true for hundreds of billions of years, if not trillions, due to the way stars burn their atomic fuel. Even if you don't include atomic helium as a molecule, the second most prevalent would likely be the most reactive combination of hydrogen and nitrogen/carbon.
    - dangrossman 11y ago
      Atomic helium is not a molecule. Oxygen is significantly more abundant than either nitrogen or carbon in the universe. In the interstellar clouds that give rise to stars, hydrogen runs into a lot more oxygen than carbon or nitrogen, so you're going to end up with more water than any other molecule but hydrogen gas. https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Abundance_of_elements_in_the_Universe https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem... Also see this delightful comment by logfromblammo: https://news.ycombinator.com/item?id=10292067 https://news.ycombinator.com/item?id=10292067

danenania 11y ago

Water is necessary for all "life as we know it". There could be configurations we don't know about that allow life to form from radically different constituents. The universe is big enough to allow for the possibility, but it's so theoretical that we have no framework for understanding how these kinds of exotic lifeforms would work or how to look for evidence of their existence. So while we shouldn't exclude the possibility, "life as we know it" is the most sensible place to start.

maaku 11y ago

Earth life is aquatic. Our chemistry happens immersed in water. When life left the oceans, living beings like you and I took the water with us. We are walking bags of water: approx 75% by weight. Of course martian life could be different than terran life, and that would be interesting too. But there are reasons to suspect that liquid chemical reactions was necessary at the genesis of life, and water is a uniquely optimal liquid for this purpose. A martian virus is unlikely to do anything to your immune system. For one thing it is unlikely that the virus would even use the same genetic codes (A C T G) as terran DNA, unless we share a common ancestor, and even in that case it wouldn't do anything against you & your immune system would eventually create an antibody and wipe it out. We fear things like bird flu and swine flu because they develop in close proximity to humans in analogous systems, honing attack vectors specifically targeting some weakness of the animal body. An alien virus would likewise be good at attacking aliens, not us.

eddd 11y ago
I would rather say, that the fear of the unknown is playing major part. Any maybe too much sci-fi movies.

jerf 11y ago

You know that science fiction trope of the deadly planet full of life where every last life form is trying to kill every other life form, and they've evolved a frightful array of offenses and defenses to do it? That planet is Earth. The real Earth. We perceive our ecosystem as friendly only because we've co-evolved with it. It is in objective terms a vicious, vicious place, with every cubic centimeter of any useful resource contended for by thousands or millions of organisms, fighting each other in every conceivable chemical, biological, and physical manner, and in particularly sophisticated corners of the Earth ecosystem, even social manners. It may look peaceful from the apex, but it's not when you get close. The likelihood of some sort of Martian bacteria getting here and causing amazing problems can never quite be eliminated, but it's very, very low. Plus, if Martian life ever existed, it actually won't be entirely disconnected from Earth life due to what you could call "transpermia": http://users.tpg.com.au/users/horsts/swaprock.html http://users.tpg.com.au/users/horsts/swaprock.html In fact if life is discovered on Mars, the next question is whether it is just Earth life that hitched a ride and managed to adapt to conditions that aren't necessarily all that much harsher than conditions we've found life on here on Earth. It's interesting either way, but the implications are hugely different between some hitchhiking Earth life vs. life that clearly came from a different abiogenesis event.