Non-Carbon-Based Life

[JMBuilder]

We live in what we call the "Goldilocks" zone, a distance just far enough away from a sun to sustain carbon-based life. However, there may be multiple types of Goldilocks zones for something quite interesting.

Non-carbon-based life.

This topic has been discussed for decades. Could a celestial body with entirely different conditions from those of Earth still be habitable for an exotic form of life?

I believe it to be quite possible. On a planet further away from a sun than Earth with much colder temperatures and seas of liquid ammonia, life based on boron or nitrogen could thrive. On a blistering hot planet closer to the sun, life based on tungsten, silicon, or iron could exist.

Discuss!

Edited June 25, 2014 by JMBuilder

[SargeRho]

Silicon, because it's chemically very similar to Carbon, allowing for many very similar reactions and compounds.

[AngelLestat]

what about digital, memeric, or any other kind of replicator?

[Skyler4856]

Silicon due to its relative versatility, and abundance, also due to its similarity to carbon.

For further reading past my behemoth sentence:

http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry

[phoenix_ca]

Silicon, because it's chemically very similar to Carbon, allowing for many very similar reactions and compounds.

The problem with silicon as a base for life is the amount of energy required to actually make and break bonds with it, among other things.

Not that I'd discount the idea of other life entirely, it's just that we don't even know how the heck carbon-based life ever got started, and we can barely judge whether or not it could exist on certain other worlds. The "Goldilocks" zone is something of a myth too, or at least a rather well debunked idea. The initial idea was based on the assumption that all life as we knew it depended on the sun for energy. Get too far away and it would be impossible for it to exist. However, deep sea exploration proved all that wrong when we found entire ecosystems underwater in the pitch black, that were based on chemosynthesis. That discovery pretty much blew-apart the idea of planets needing to be in a special zone away from their star to possibly harbour life. Europa, for all we know, could very well support life in a liquid ocean underneath its ice, supported by the heat generated by tidal forces.

[lajoswinkler]

Silicon, but it just won't happen. Carbon is abundant and it's a lot more (I mean A LOT MORE) better at making various compounds. It is simply the most suitable element for life and that's why life exists using carbon.

[JMBuilder]

Could carbon based life exist in temperatures where ammonia is a liquid?

[lajoswinkler]

Could carbon based life exist in temperatures where ammonia is a liquid?

The state of matter depends on the pressure, too, but if we ignore the ultrahigh pressures of diamond anvils, I think there is a potential for something like that. Ammonia is similar to water. It's polar, and that's extremely important for life. Polar solvent gives huge versatility to the system.

[Armchair Rocket Scientist]

We live in what we call the "Goldilocks" zone, a distance just far enough away from a sun to sustain carbon-based life. However, there may be multiple types of Goldilocks zones for something quite interesting.

Non-carbon-based life.

This topic has been discussed for decades. Could a celestial body with entirely different conditions from those of Earth still be habitable for an exotic form of life?

I believe it to be quite possible. On a planet further away from a sun than Earth with much colder temperatures and seas of liquid ammonia, life based on boron or nitrogen could thrive. On a blistering hot planet closer to the sun, life based on tungsten, silicon, or iron could exist.

Discuss!

Well, boron is fairly rare, and tungsten is extremely rare, so I don't think either of them are good candidates.

Nitrogen seems unlikely without carbon being involved as well, since complex nitrogen-containing molecules with no carbon seem to mostly be high explosives.

[JMBuilder]

To me, the most feasible alternative to carbon is a combination of boron and nitrogen. Boron has an affinity for ammonia as a solvent, and ammonia contains nitrogen, which can form covalent bonds with boron similar to carbon-carbon bonds. Boron can also form three-center two-electron bonds, increasing its potential to form complex molecules. Boron compounds are highly explosive on Earth, so a much colder planet is a better candidate for this type of life. As for boron's low cosmic abundance, a star system with increased levels of cosmic ray spallation would solve a large portion of that problem.

As I said in the original post, silicon based life is more likely to survive on a hotter planet. Large amounts of heat could reduce the amount of chemical energy needed to make and break silicon bonds. Carbon molecules on a hotter planet would most likely be denatured.

Edited June 25, 2014 by JMBuilder

[Tommygun]

Well, boron is fairly rare, and tungsten is extremely rare, so I don't think either of them are good candidates.

Nitrogen seems unlikely without carbon being involved as well, since complex nitrogen-containing molecules with no carbon seem to mostly be high explosives.

Intelligent plastic explosives, the ultimate smart bomb.

-I've always wondered if complex life could evolve on a planet with a dense chlorine atmosphere.

I know some scientist think a chlorine atmosphere would make oceans too salty for complex life to thrive.

Maybe copper based blood with a chlorine atmosphere too?

[lajoswinkler]

-I've always wondered if complex life could evolve on a planet with a dense chlorine atmosphere.

I know some scientist think a chlorine atmosphere would make oceans too salty for complex life to thrive.

Maybe copper based blood with a chlorine atmosphere too?

No. Chlorine can not exist in its elemental form in any environment. (Let's ignore ephemeral and minute occurences here and there.)

It's a fiercely reactive element and as soon as it's exposed to the nature, it binds with something. That's usually water.

It will react with planetary ices and hydrogen.

Even if such atmosphere was possible, life could not form in it. Life requires a versatility of reaction energies, various states and couplings of molecules. All chlorine can do is to appear and ****up everything like a mad man.

[helaeon]

I once thought that life using alternative elements to facilitate the chemistry of life was possible, then I got a biochemistry degree.

None of the above. The answer is none of the above. Life will have to be carbon based because:

That 2nd row of the periodic table is special. Carbon, Nitrogen, Oxygen, Fluorine in particular. Those second shell orbitals do some interesting things and allow for strong bonding and strong association to the nuclei sharing that electron (as there are only 2 other electrons in the 1s orbital blocking them from the nucleus). Carbon has something very special in its valence orbital hybridizing its s and p orbitals to create the tetrahedral bonding pattern, as well as being able to combine them different ways to create double and triple bonds. All of this allows for the extreme number of stable, covalent compounds with many many bonds allowing for macromolecules such as proteins.

Something like silicon which has a similar valence orbital holds those electrons too weakly it can't do the chains (it behaves too much like a metal because the entire 2 s and 2 p orbitals are filled and blocking the nucleus from anything that bonds to it, which is what happens as you go down the periodic table and there are fewer and fewer non-metals until there are none). Nitrogen is capable of 3 bonds at a time but it really only behaves in that way when bonded to and around Carbon. When you start getting into N-N bonds nature wants to make nitrogen gas so those compounds are not super stable so chains are not going to happen with only nitrogen either. Oxygen does the same. And Fluorine is stupid reactive and a huge electron hog, and only capable of sharing one electron so no chains there either.

Each element on the periodic table is special with special properties. At something like molecular scale chemistry which is what proteins do, your material selection must be perfect. There is only one atom that will suffice. It's one reason we have micronutrients like cobalt and manganese. There are reactions in our bodies that REQUIRE that to work and nothing else will do. Best is going to win out. In this case Carbon is the best, possibly only choice as the backbone of biological macromolecules.

Now that doesn't mean there aren't chemistries involving carbon and molecules, particularly macromolecules, never seen or imagined on Earth. Another life form may use molecules other than amino acids, starches, sugars, etc to build something that is clearly life. I think this is highly probable actually. But those molecules will contain a lot of carbon. I'm not even convinced that water is necessary as a solvent, and if that were the case then you'd see chemistries entirely alien to what we know. This is why I won't rule out things like the chlorine atmosphere issue, but chlorine is almost as bad as fluorine and I don't see anything surviving in a fluorine atmosphere because I don't think life could start because it is SO reactive. But evolve to use it... maybe? Possibly in place of something like oxygen. It would control the step down to fluorination or chlorination rather than oxidation. Though halogens behave differently than oxygen and sulfur do in organic molecules and that may not work at all, but it's at least on the table I think. The energy demands to dechlorinate or defluorinate to create a cycle like we have on Earth with oxygen would be huge and stepping it down like the Krebs Cycle and fermentation do may not be possible. But, I would say this is actually far more possible than a life form that uses something other than carbon as the main building material in its macromolecules.

Boron can form multiple bonds but those get weak over distance. You don't see the nearly bond agnostic bonds like you see in carbon where you are gluing stuff together, the electrons shift around but its a localized effect they don't cluster causing the molecule to not accept any more bonds. Biggest problem is with 3 bonds you are not going to be making 3 dimensional molecules (they'll be planar 120 degrees between bonds, or straight with one double bond and 1 single bond). 3d molecules particularly the idea of chirality are absolutely critical in biomolecules (the "order" the bonds are in matter, you get a different molecule because it's shaped differently even though the formula of the compound is the same). Boron does have some cool organic synthesis applications though but it won't be the backbone. You need something that can do at least 4 bonds of equal strength (depending on bonding partner of course).

Edited June 27, 2014 by helaeon
Add bit about boron

[Moss]

Well that clears all of this up.

[lajoswinkler]

...This is why I won't rule out things like the chlorine atmosphere issue...

I don't want to sound bad (because you've made some great statements that have cleared things a lot; thank you for putting a cork into the mouths of people who like to troll on threads like this), but as someone supposedly with a biochemistry degree, you don't seem to understand the basics of geology which are heavily immersed into inorganic chemistry, and you should. You need to know these things.

Chlorine can not form atmospheres. Period.

[JMBuilder]

I once thought that life using alternative elements to facilitate the chemistry of life was possible, then I got a biochemistry degree.

None of the above. The answer is none of the above. Life will have to be carbon based because:

That 2nd row of the periodic table is special. Carbon, Nitrogen, Oxygen, Fluorine in particular. Those second shell orbitals do some interesting things and allow for strong bonding and strong association to the nuclei sharing that electron (as there are only 2 other electrons in the 1s orbital blocking them from the nucleus). Carbon has something very special in its valence orbital hybridizing its s and p orbitals to create the tetrahedral bonding pattern, as well as being able to combine them different ways to create double and triple bonds. All of this allows for the extreme number of stable, covalent compounds with many many bonds allowing for macromolecules such as proteins.

Something like silicon which has a similar valence orbital holds those electrons too weakly it can't do the chains (it behaves too much like a metal because the entire 2 s and 2 p orbitals are filled and blocking the nucleus from anything that bonds to it, which is what happens as you go down the periodic table and there are fewer and fewer non-metals until there are none). Nitrogen is capable of 3 bonds at a time but it really only behaves in that way when bonded to and around Carbon. When you start getting into N-N bonds nature wants to make nitrogen gas so those compounds are not super stable so chains are not going to happen with only nitrogen either. Oxygen does the same. And Fluorine is stupid reactive and a huge electron hog, and only capable of sharing one electron so no chains there either.

Each element on the periodic table is special with special properties. At something like molecular scale chemistry which is what proteins do, your material selection must be perfect. There is only one atom that will suffice. It's one reason we have micronutrients like cobalt and manganese. There are reactions in our bodies that REQUIRE that to work and nothing else will do. Best is going to win out. In this case Carbon is the best, possibly only choice as the backbone of biological macromolecules.

Now that doesn't mean there aren't chemistries involving carbon and molecules, particularly macromolecules, never seen or imagined on Earth. Another life form may use molecules other than amino acids, starches, sugars, etc to build something that is clearly life. I think this is highly probable actually. But those molecules will contain a lot of carbon. I'm not even convinced that water is necessary as a solvent, and if that were the case then you'd see chemistries entirely alien to what we know. This is why I won't rule out things like the chlorine atmosphere issue, but chlorine is almost as bad as fluorine and I don't see anything surviving in a fluorine atmosphere because I don't think life could start because it is SO reactive. But evolve to use it... maybe? Possibly in place of something like oxygen. It would control the step down to fluorination or chlorination rather than oxidation. Though halogens behave differently than oxygen and sulfur do in organic molecules and that may not work at all, but it's at least on the table I think. The energy demands to dechlorinate or defluorinate to create a cycle like we have on Earth with oxygen would be huge and stepping it down like the Krebs Cycle and fermentation do may not be possible. But, I would say this is actually far more possible than a life form that uses something other than carbon as the main building material in its macromolecules.

Boron can form multiple bonds but those get weak over distance. You don't see the nearly bond agnostic bonds like you see in carbon where you are gluing stuff together, the electrons shift around but its a localized effect they don't cluster causing the molecule to not accept any more bonds. Biggest problem is with 3 bonds you are not going to be making 3 dimensional molecules (they'll be planar 120 degrees between bonds, or straight with one double bond and 1 single bond). 3d molecules particularly the idea of chirality are absolutely critical in biomolecules (the "order" the bonds are in matter, you get a different molecule because it's shaped differently even though the formula of the compound is the same). Boron does have some cool organic synthesis applications though but it won't be the backbone. You need something that can do at least 4 bonds of equal strength (depending on bonding partner of course).

Do you think that alternating boron-nitrogen molecules would be complex enough?

[bs1110101]

No. Chlorine can not exist in its elemental form in any environment. (Let's ignore ephemeral and minute occurences here and there.)

It's a fiercely reactive element and as soon as it's exposed to the nature, it binds with something. That's usually water.

It will react with planetary ices and hydrogen.

Even if such atmosphere was possible, life could not form in it. Life requires a versatility of reaction energies, various states and couplings of molecules. All chlorine can do is to appear and ****up everything like a mad man.

Isn't the same true to a lesser extent with oxygen? I think i chlorine atmosphere could totally happen, though there'd have to be a something of a cycle of plant like things consuming the chlorine compounds in the atmosphere and belching out chlorine gas.

[lajoswinkler]

Isn't the same true to a lesser extent with oxygen? I think i chlorine atmosphere could totally happen, though there'd have to be a something of a cycle of plant like things consuming the chlorine compounds in the atmosphere and belching out chlorine gas.

No. Reactivity of chlorine is much more intensive than of oxygen when it's exposed to planetary rock and ices. It will quickly react with water and it will attack silicates, oxides, metals, just about anything that makes up planets.

Oxygen would linger around probably for thousands of years or even more, before the crust absorbs it.

Chlorine would probably be gone in less than a year, and I'm being generous here.

Any lifeform capable of oxidizing chlorine could not be based on aqueous medium, and that extremely narrows the whole thing down to few ideas. Water is everywhere and if something is going to evolve from simple chemicals, it basically can not avoid it.

[JMBuilder]

Mercury could be a potential habitat for silicon-based life. It is 70% metallic and 30% silicate. It has no gaseous atmosphere. Instead it has a thin exosphere of a variety of elements, including silicon, hydrogen, oxygen, calcium, and many others. This would prevent silicon from forming too many bonds with oxygen.

As for silicon having low versatility, the intense heat and radiation from the sun might excite the electrons enough to enhance its versatility. Covalent bonds might be easier to form in this situation.

The life itself would most likely be photosynthetic, and would rely on nutrients like calcium, sodium, potassium, magnesium, oxygen, hydroxide, iron, and, of course, silicon. It would probably have a silicate or iron-oxide exoskeleton and inner cells of silicon, iron, oxygen, and maybe calcium. Instead of blood, it would have magnetic pathways and gradients for transporting nutrients and waste.

[Chiboko]

We live in what we call the "Goldilocks" zone, a distance just far enough away from a sun to sustain carbon-based life.

On the subject of the goldilocks zone it turns out that, at least for carbon based life like that found on earth, the goldilocks zone shifts depending on how much water is on the planet. It is possible to have something resembling earth like life on a planet closer to its sun than mercury as long as the amount of water on the planet is very low; Such a planet would most likely be tidally locked to its parent star and life would probably inhabit a thin line on the border of the day and night sides of the planet where temperatures are low enough to facilitate the condensation of water. The same principle works in reverse as you get further from a parent star but also requires a thicker atmosphere to trap more heat to stop water freezing.

On another note, as far as earths own habitable zone is concerned we are right on the hot inner edge of it.

(Not a scientist, possibly out of date)

[lajoswinkler]

Mercury could be a potential habitat for silicon-based life. It is 70% metallic and 30% silicate. It has no gaseous atmosphere. Instead it has a thin exosphere of a variety of elements, including silicon, hydrogen, oxygen, calcium, and many others. This would prevent silicon from forming too many bonds with oxygen.

As for silicon having low versatility, the intense heat and radiation from the sun might excite the electrons enough to enhance its versatility. Covalent bonds might be easier to form in this situation.

No.

"Versatility" isn't what you're describing, and the bonds silicon forms are weaker than carbon's, so on fried Mercury surface it would not be possible.

Also, you need a solvent for life. There are no solvents on Mercury surface. Additionally, it's bathed in intense solar wind and hard UV.

There might be something beneath the surface near the poles, but chances are there isn't anything.

The life itself would most likely be photosynthetic, and would rely on nutrients like calcium, sodium, potassium, magnesium, oxygen, hydroxide, iron, and, of course, silicon. It would probably have a silicate or iron-oxide exoskeleton and inner cells of silicon, iron, oxygen, and maybe calcium. Instead of blood, it would have magnetic pathways and gradients for transporting nutrients and waste.

Yeah... that has about the same amount of reality in it as the inner workings of a tooth fairy, so I don't feel there's the need to bust every single detail of it.

[JMBuilder]

Could hydrochloric acid be a solvent?

[lajoswinkler]

Could hydrochloric acid be a solvent?

Hydrochloric acid is an aqueous solution of hydrogen chloride, so, yes. It is a solvent.

At standard conditions of temperature and pressure, you can make it around 40%. At higher pressures and lower temperatures the percentage can go higher.

[JMBuilder]

Oh, wait a second. I just had a thought. Could hydroxide (OH-) act as a solvent?

[Kryten]

Hydroxide can't exist as a pure material, at least under any reasonable planetary conditions. Unless it's already in a solvent, it's going to be part of a solid.