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Perhaps someone with a stronger chemistry or biological background can clear this up for me: do we assume extraterrestrial life will rely on the same chemistry

Perhaps someone with a stronger chemistry or biological background can clear this up for me: do we assume extraterrestrial life will rely on the same chemistry as earthen life simply by virtue of limited observation? Is there some evidence that life, given a different starting planet, would like still form from chemicals readily found on earth? Or, i suppose, does it just make for clickable headlines?

iwwr 12y ago
Organic components prevalent in one kind of chirality may be a give-away for life-like processes. As would unusual concentrations for hard to synthesize components. Also, a surface under significant chemical disequilibrium (oxygen and reduced carbon (plant matter) in close proximity).
netcraft 12y ago
I believe it is theorized that life could use silicon instead of carbon, but I think for the most part we just look for what we know works. They are just saying that earth life could have lived on Mars at some point in the past, that the conditions would have been favorable for it. Other kinds of life could exist in other environments, but we don't have any litmus for those observations yet.
- Gravityloss 12y ago
  The problem is that silicon dioxide is a solid unlike carbon dioxide. "Breathing" it out is a lot harder.
  - torrente 12y ago
    Why would you assume these organisms would breathe?
    - jerf 12y ago
      Because all organisms need to expel entropy to survive, and expelling solid entropy is a fairly non-trivial engineering problem vs. the life that we do know expelling it via liquids and gasses. Heck, it's not even all that clear how to do that just as a machine... nothing is coming to mind that does that today. (Examples welcomed. Also note that for today's discussion execrement is solids suspended in a liquid, not a "solid". Silicon is a solid, you know, rock-solid, literally.) The idea that we have "no idea" what life could look like out there in the universe is grossly oversold. We actually can put a lot of bounds on them, using rigorous mathematics, and discuss them despite not necessarily knowing all the chemical details.
      - torrente 12y ago
        The idea that we have "no idea" what life could look like out there in the universe is grossly oversold. We actually can put a lot of bounds on them, using rigorous mathematics, and discuss them despite not necessarily knowing all the chemical details. Do you have any sources that discuss this?
      - ars 12y ago
        > Heck, it's not even all that clear how to do that just as a machine... nothing is coming to mind that does that today. That's basically ash, think of a coal burning plant and how they deal with waste. Or iron smelting, how they leave the waste slag behind.
        redler 12y ago
        Or a Horta.
        jerf 12y ago
        Bingo. Thanks. I knew there had to be something. It's difficult to see how this could be made to work for a life form, because this is a very macroscopic process. On a microscopic level, well, we're all just ugly bags of mostly-water so we do it by suspending things in our mostly-water. As I understand it there are few to no good candidates for a silicon-friendly liquid base when you work through it. (Interestingly, I have seen some suggestions that there could be other liquids that carbon-based life could be based on, such as ammonia. That said, it may not be coincidence that water is still almost certainly the best (accounting for the possibility that it's just the observer effect), and that's what all life forms reading this for the forseeably future are based on.)
    - deleted 12y ago
      [deleted]
    - Gravityloss 12y ago
      Matter exchange is quite necessary for life, and exchanging gases can be a lot easier than exchanging solids.
  - ankurpatel 12y ago
    Solid at our temperature but at higher temperatures it can be liquid and gas.
  - jessaustin 12y ago
    The problem is that silicon dioxide is a solid unlike carbon dioxide. I'm not a chemist, but by analogy with anaerobic bacteria we have on Earth, some of which produce methane gas, one could imagine something that expels silane gas.
- netcraft 12y ago
  Here is a wikipedia link about hypothetical types of biochemistry: https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...
- kazinator 12y ago
  Life could perhaps also just use a computer, and exists entirely as software. The computer could be implemented with something other than atoms, perhaps. Maybe some particles shooting among the neutrons of a white dwarf star or something. (My point here is that life doesn't have to be chemical, based on the elements and compounds.) However, for chemical life, there are indeed only a few ways. We understand the elements very well and the kinds of combinations they express: what kinds of chemistry are possible for all the elements. Only a few elements exhibit the expressive variety of molecular forms that plausibly support the complex structures that are arguably needed for the chemical representation of life.
  - dandelany 12y ago
    Presumably such a computer would have to have been created by some extremely complex self-organizing system. I think we would call such a system "life" long before it was complex enough to turn a star into a computer (ignoring the thermodynamic problems with such a proposal).
    - jarin 12y ago
      It's not impossible for it to form by itself, but it's pretty unlikely: https://en.wikipedia.org/wiki/Boltzmann_brain https://en.wikipedia.org/wiki/Boltzmann_brain
  - gee_totes 12y ago
    Wouldn't it be ironic if that computer seeded life across the universe in the hopes that it would evolve to someday create computers.
jarin 12y ago
Not necessarily, it's just that Earth-like biology is the only one we know is absolutely possible.
lmkg 12y ago
We know what Earth-like life looks like, and some of the indirect evidence it leaves, so we know how to detect it. This means that we can actually build an instrument that looks for it. We have no way of detecting non-Earth-like life because we have no idea what we're looking for. It's simply not a tractable problem. I mean, if we found something walking around, or even radio signals, we could guess that's life. But detecting chemicals in samples of sand? We haven't the first clue what sort of tests to even run.
- JoeAltmaier 12y ago
  That's a stretch. Non-earth life can be predicted pretty well. Its organic or silicon very likely, and those chemistries depend on things. Like Nitrogen.
  - Mahn 12y ago
    But that's exactly his point, non-earth life that behaves like life on earth can be predicted easily, but anything beyond that, who knows? You can only assume non-earth life depends on things like Nitrogen if you believe that's the only kind of life that can form, but we don't know that.
    - vacri 12y ago
      Once you get into those semantics, you actually need to start nailing down what is required to determine that something is 'alive'. For example, does it grow? Tin whiskers grow, but they're not alive. I remember in my high-school chemistry class, my teacher showed us one seven-point list for defining life, which looked sane to us, then described a two-atom autocatalysing molecule which satisfied it. I can't recall all the points, but it had reproduction satisfied via the autocatalysis. It assembled new versions of itself from component materials just like an animal does through gestating. I haven't kept a tag on the literature in the area, but I imagine that there's been no great breakthrough in how to unambiguously describe what people mean when they say 'life', let alone 'non-earth life'.
      - 12y ago
uptown 12y ago
"Life" is just a word to describe what we know as "life". Anything else might require a new word even though that being might consider itself to also be "life".
subnaught 12y ago
You're absolutely right that, if we define life generally as a self-replicating system implemented in chemistry, there is no a priori reason to assume that extraterrestrial life would use the same elements as we do. However, there are a couple good reasons that this might be the case: Abundance - Broadly speaking, the prevalence of an element decreases with its atomic mass, which means that, while elemental availability will differ from planet to planet, lighter elements will always be more abundant. Thus, statistically speaking, it is likely that extraterrestrial life uses C,H,N,O just as we do. Bonding - When you study the chemical bonding of elements in relation to their position in the periodic table, what you realize is the "first row," i.e. C,N,O, is actually an exception and the rest of the periodic table is the rule. What this means in practice is that these elements are capable of a much greater diversity in bonding than those below. It is this diversity that allows for the development of the complex biomolecular machinery necessary for life. Edit: Here's a great essay by Nobel laureate Roald Hoffmann on the differences between Si and C and the implications for life: http://pubs.acs.org/cen/80th/print/silicon.html http://pubs.acs.org/cen/80th/print/silicon.html
- ars 12y ago
  It's more than just light elements, those elements are the main sequence elements made by Stellar nucleosynthesis. If you look here, you'll see just how abundant they are compared to everything else: 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...
  - jonalmeida 12y ago
    Been a while since chem & physics class for me as well. How are these estimations calculated, and to what certainty? Surely, these are calculations only from the observable universe?
    - ars 12y ago
      I'm not sure how they know, but see here: https://en.wikipedia.org/wiki/Stellar_nucleosynthesis https://en.wikipedia.org/wiki/Stellar_nucleosynthesis for the reason for the quantities.
kingzain 12y ago
Related: https://www.youtube.com/watch?v=2LGQrVSxPvg https://www.youtube.com/watch?v=2LGQrVSxPvg Neil deGrasse Tyson explains it quite nicely.
deleted 12y ago
[deleted]
kazinator 12y ago
Whether "Earth-like" life exists somewhere else is a legitimate, separate question, from whether any kind of life exists somewhere else. There is a vested interest too in Mars having biologically useful forms of nitrogen, because that has implications toward being able to colonize Mars with Earth life. It is reasonable to be excited about discoveries like organic molecules with multiple C-C bonds existing elsewhere.
GregBuchholz 12y ago
One reason for thinking that life on Mars might be similar to life on Earth is if they both had a common origin. This would be made possible by their relatively close proximity. Bacteria could have been transported between planets by traveling on meteorites. See also: https://en.wikipedia.org/wiki/Martian_meteorite https://en.wikipedia.org/wiki/Martian_meteorite https://en.wikipedia.org/wiki/Panspermia https://en.wikipedia.org/wiki/Panspermia
InclinedPlane 12y ago
It's not impossible that life might exist based on other foundations than the ones we've witnessed, but there is some compelling evidence that carbon based life should be the more common form. Firstly, carbon based chemistry is far and away richer than any other type of chemistry, there are an essentially infinite number of different carbon based compounds, and they span an enormous array of properties and chemical activities. Secondly, the raw ingredients for those chemicals are extremely common throughout the Universe. Moreover, natural processes produce the basic building blocks of life routinely. Additionally, we see from the history on Earth that almost as soon as conditions suitable for life to exist came into being then it wasn't long before life started. It's difficult to draw conclusions from just one data point but that may indicate that the process of biogenesis is fairly straightforward, under the right conditions. The bias towards focusing on carbon based life comes because the route to such life seems straightforward, and makes use of abundant naturally occurring compounds, while at the same time we have not even the slightest hint of how naturally occurring non-carbon-based life would even be possible.

iwwr 12y ago

Organic components prevalent in one kind of chirality may be a give-away for life-like processes. As would unusual concentrations for hard to synthesize components. Also, a surface under significant chemical disequilibrium (oxygen and reduced carbon (plant matter) in close proximity).

netcraft 12y ago

I believe it is theorized that life could use silicon instead of carbon, but I think for the most part we just look for what we know works. They are just saying that earth life could have lived on Mars at some point in the past, that the conditions would have been favorable for it. Other kinds of life could exist in other environments, but we don't have any litmus for those observations yet.

Gravityloss 12y ago
The problem is that silicon dioxide is a solid unlike carbon dioxide. "Breathing" it out is a lot harder.
- torrente 12y ago
  Why would you assume these organisms would breathe?
  - jerf 12y ago
    Because all organisms need to expel entropy to survive, and expelling solid entropy is a fairly non-trivial engineering problem vs. the life that we do know expelling it via liquids and gasses. Heck, it's not even all that clear how to do that just as a machine... nothing is coming to mind that does that today. (Examples welcomed. Also note that for today's discussion execrement is solids suspended in a liquid, not a "solid". Silicon is a solid, you know, rock-solid, literally.) The idea that we have "no idea" what life could look like out there in the universe is grossly oversold. We actually can put a lot of bounds on them, using rigorous mathematics, and discuss them despite not necessarily knowing all the chemical details.
    - torrente 12y ago
      The idea that we have "no idea" what life could look like out there in the universe is grossly oversold. We actually can put a lot of bounds on them, using rigorous mathematics, and discuss them despite not necessarily knowing all the chemical details. Do you have any sources that discuss this?
    - ars 12y ago
      > Heck, it's not even all that clear how to do that just as a machine... nothing is coming to mind that does that today. That's basically ash, think of a coal burning plant and how they deal with waste. Or iron smelting, how they leave the waste slag behind.
      - redler 12y ago
        Or a Horta.
      - jerf 12y ago
        Bingo. Thanks. I knew there had to be something. It's difficult to see how this could be made to work for a life form, because this is a very macroscopic process. On a microscopic level, well, we're all just ugly bags of mostly-water so we do it by suspending things in our mostly-water. As I understand it there are few to no good candidates for a silicon-friendly liquid base when you work through it. (Interestingly, I have seen some suggestions that there could be other liquids that carbon-based life could be based on, such as ammonia. That said, it may not be coincidence that water is still almost certainly the best (accounting for the possibility that it's just the observer effect), and that's what all life forms reading this for the forseeably future are based on.)
  - deleted 12y ago
    [deleted]
  - Gravityloss 12y ago
    Matter exchange is quite necessary for life, and exchanging gases can be a lot easier than exchanging solids.
- ankurpatel 12y ago
  Solid at our temperature but at higher temperatures it can be liquid and gas.
- jessaustin 12y ago
  The problem is that silicon dioxide is a solid unlike carbon dioxide. I'm not a chemist, but by analogy with anaerobic bacteria we have on Earth, some of which produce methane gas, one could imagine something that expels silane gas.
netcraft 12y ago
Here is a wikipedia link about hypothetical types of biochemistry: https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...
kazinator 12y ago
Life could perhaps also just use a computer, and exists entirely as software. The computer could be implemented with something other than atoms, perhaps. Maybe some particles shooting among the neutrons of a white dwarf star or something. (My point here is that life doesn't have to be chemical, based on the elements and compounds.) However, for chemical life, there are indeed only a few ways. We understand the elements very well and the kinds of combinations they express: what kinds of chemistry are possible for all the elements. Only a few elements exhibit the expressive variety of molecular forms that plausibly support the complex structures that are arguably needed for the chemical representation of life.
- dandelany 12y ago
  Presumably such a computer would have to have been created by some extremely complex self-organizing system. I think we would call such a system "life" long before it was complex enough to turn a star into a computer (ignoring the thermodynamic problems with such a proposal).
  - jarin 12y ago
    It's not impossible for it to form by itself, but it's pretty unlikely: https://en.wikipedia.org/wiki/Boltzmann_brain https://en.wikipedia.org/wiki/Boltzmann_brain
- gee_totes 12y ago
  Wouldn't it be ironic if that computer seeded life across the universe in the hopes that it would evolve to someday create computers.

jarin 12y ago

Not necessarily, it's just that Earth-like biology is the only one we know is absolutely possible.

lmkg 12y ago

We know what Earth-like life looks like, and some of the indirect evidence it leaves, so we know how to detect it. This means that we can actually build an instrument that looks for it. We have no way of detecting non-Earth-like life because we have no idea what we're looking for. It's simply not a tractable problem. I mean, if we found something walking around, or even radio signals, we could guess that's life. But detecting chemicals in samples of sand? We haven't the first clue what sort of tests to even run.

JoeAltmaier 12y ago
That's a stretch. Non-earth life can be predicted pretty well. Its organic or silicon very likely, and those chemistries depend on things. Like Nitrogen.
- Mahn 12y ago
  But that's exactly his point, non-earth life that behaves like life on earth can be predicted easily, but anything beyond that, who knows? You can only assume non-earth life depends on things like Nitrogen if you believe that's the only kind of life that can form, but we don't know that.
  - vacri 12y ago
    Once you get into those semantics, you actually need to start nailing down what is required to determine that something is 'alive'. For example, does it grow? Tin whiskers grow, but they're not alive. I remember in my high-school chemistry class, my teacher showed us one seven-point list for defining life, which looked sane to us, then described a two-atom autocatalysing molecule which satisfied it. I can't recall all the points, but it had reproduction satisfied via the autocatalysis. It assembled new versions of itself from component materials just like an animal does through gestating. I haven't kept a tag on the literature in the area, but I imagine that there's been no great breakthrough in how to unambiguously describe what people mean when they say 'life', let alone 'non-earth life'.
    - 12y ago

uptown 12y ago

"Life" is just a word to describe what we know as "life". Anything else might require a new word even though that being might consider itself to also be "life".

subnaught 12y ago

You're absolutely right that, if we define life generally as a self-replicating system implemented in chemistry, there is no a priori reason to assume that extraterrestrial life would use the same elements as we do. However, there are a couple good reasons that this might be the case: Abundance - Broadly speaking, the prevalence of an element decreases with its atomic mass, which means that, while elemental availability will differ from planet to planet, lighter elements will always be more abundant. Thus, statistically speaking, it is likely that extraterrestrial life uses C,H,N,O just as we do. Bonding - When you study the chemical bonding of elements in relation to their position in the periodic table, what you realize is the "first row," i.e. C,N,O, is actually an exception and the rest of the periodic table is the rule. What this means in practice is that these elements are capable of a much greater diversity in bonding than those below. It is this diversity that allows for the development of the complex biomolecular machinery necessary for life. Edit: Here's a great essay by Nobel laureate Roald Hoffmann on the differences between Si and C and the implications for life: http://pubs.acs.org/cen/80th/print/silicon.html http://pubs.acs.org/cen/80th/print/silicon.html

ars 12y ago
It's more than just light elements, those elements are the main sequence elements made by Stellar nucleosynthesis. If you look here, you'll see just how abundant they are compared to everything else: 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...
- jonalmeida 12y ago
  Been a while since chem & physics class for me as well. How are these estimations calculated, and to what certainty? Surely, these are calculations only from the observable universe?
  - ars 12y ago
    I'm not sure how they know, but see here: https://en.wikipedia.org/wiki/Stellar_nucleosynthesis https://en.wikipedia.org/wiki/Stellar_nucleosynthesis for the reason for the quantities.

kingzain 12y ago

Related: https://www.youtube.com/watch?v=2LGQrVSxPvg https://www.youtube.com/watch?v=2LGQrVSxPvg Neil deGrasse Tyson explains it quite nicely.

deleted 12y ago

[deleted]

kazinator 12y ago

Whether "Earth-like" life exists somewhere else is a legitimate, separate question, from whether any kind of life exists somewhere else. There is a vested interest too in Mars having biologically useful forms of nitrogen, because that has implications toward being able to colonize Mars with Earth life. It is reasonable to be excited about discoveries like organic molecules with multiple C-C bonds existing elsewhere.

GregBuchholz 12y ago

One reason for thinking that life on Mars might be similar to life on Earth is if they both had a common origin. This would be made possible by their relatively close proximity. Bacteria could have been transported between planets by traveling on meteorites. See also: https://en.wikipedia.org/wiki/Martian_meteorite https://en.wikipedia.org/wiki/Martian_meteorite https://en.wikipedia.org/wiki/Panspermia https://en.wikipedia.org/wiki/Panspermia

InclinedPlane 12y ago

It's not impossible that life might exist based on other foundations than the ones we've witnessed, but there is some compelling evidence that carbon based life should be the more common form. Firstly, carbon based chemistry is far and away richer than any other type of chemistry, there are an essentially infinite number of different carbon based compounds, and they span an enormous array of properties and chemical activities. Secondly, the raw ingredients for those chemicals are extremely common throughout the Universe. Moreover, natural processes produce the basic building blocks of life routinely. Additionally, we see from the history on Earth that almost as soon as conditions suitable for life to exist came into being then it wasn't long before life started. It's difficult to draw conclusions from just one data point but that may indicate that the process of biogenesis is fairly straightforward, under the right conditions. The bias towards focusing on carbon based life comes because the route to such life seems straightforward, and makes use of abundant naturally occurring compounds, while at the same time we have not even the slightest hint of how naturally occurring non-carbon-based life would even be possible.