Hydrothermal Vents as alternative to Fire?

[firefossil]

I've heard it argued that fire is essential to sapient life, as cooked food allows for a smaller stomach to process the same amount of calories and thus allow for a larger brain due to the effect such has on the energy budget. Similarly its argued as essential for civilization as fire enables you to smelt things and develop better tools. This would obviously be a huge damper for aquatic sapient life as fire doesn't work underwater. So my question is, could you cook food or smelt metals with a hydrothermal vent? This is assuming that you are limited only to what tools a hypothetical sapient aquatic lifeform could develop underwater without fire or whatnot.

 

[SSgtC]

Well, there's a few problems with this. The first being that most hydrothermal vents are in very deep water in the ocean. So for any species to benefit from it they need to be adapted to life at extreme pressures and in total darkness.

The second problem, is that hydrothermal vents aren't consistent. In the Pacific ocean, vents tend to slowly cool down after one to two years. So you're hypothetical species also needs to be nomadic to find fresh hot spots every year or two.

And finally is temperature. Water, especially in the amounts we're talking about, is the greatest coolant on earth. Meaning the instant the vent begins venting, it's discharge immediately begins to cool. As of ten years ago, the hottest scientists have ever observed the water around a vent to be is 407° Celcius/746° Farenheit. (Correction, they have since observed vents to briefly reach 464°C/867°F). And even then, this water was in a supercritical state trapped between a liquid and gas form. While that's certainly hot enough to cook with, it's nowhere near hot enough to smelt ore into bronze, iron or steel. The only metals it could melt are tin and lead. Everything else simply has too high a melting point. Most are double or more the highest temperature ever recorded at a vent.

 

[firefossil]

Well, there's a few problems with this. The first being that most hydrothermal vents are in very deep water in the ocean. So for any species to benefit from it they need to be adapted to life at extreme pressures and in total darkness.

The second problem, is that hydrothermal vents aren't consistent. In the Pacific ocean, vents tend to slowly cool down after one to two years. So you're hypothetical species also needs to be nomadic to find fresh hot spots every year or two.

And finally is temperature. Water, especially in the amounts we're talking about, is the greatest coolant on earth. Meaning the instant the vent begins venting, it's discharge immediately begins to cool. As of ten years ago, the hottest scientists have ever observed the water around a vent to be is 407° Celcius/746° Farenheit. (Correction, they have since observed vents to briefly reach 464°C/867°F). And even then, this water was in a supercritical state trapped between a liquid and gas form. While that's certainly hot enough to cook with, it's nowhere near hot enough to smelt ore into bronze, iron or steel. The only metals it could melt are tin and lead. Everything else simply has too high a melting point. Most are double or more the highest temperature ever recorded at a vent.

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1: Part of my asking this question is for the possibility of life in underground oceans like Europa or Enceladus, which come to think of it would have even higher pressures given the indicated depths. Or does the lower gravity cancel that out somewhat?

2: Wait if they're that shortlived how do creatures like giant tube worms survive?

3: Would it be possible to build a device that could concentrate the heat until it reaches smelting levels?

 

[SSgtC]

1: Part of my asking this question is for the possibility of life in underground oceans like Europa or Enceladus, which come to think of it would have even higher pressures given the indicated depths. Or does the lower gravity cancel that out somewhat?

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If I understood the science correctly, not a given, then yes, the higher pressures should allow for higher temperatures. Though salinity also plays role. So that would have to be taken into consideration as well. The lower specific gravity could offset the highest pressure (lower gravity=lower boiling point) but you'd have to have some solid numbers to work with to calculate whether the two factors are offsetting or whether one has a greater effect than the other.

2: Wait if they're that shortlived how do creatures like giant tube worms survive?

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Because they don't die in one or two years. They just start to cool. The life around them likely can survive at lower temperatures as the vent cools.

3: Would it be possible to build a device that could concentrate the heat until it reaches smelting levels?

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That I don't know. I tend to believe all things are possible, but my gut instinct is no. For example, to melt cast iron, you need a temperature of 2200°F. Nearly 3 times hotter than the highest temperature ever recorded at a vent. And 4-5 times hotter than the average temperatures. Wrought iron is even hotter at 2700°F. Most metals require temperatures in excess of 1200°F to melt. With most of those requiring temps in excess of 1700°. Zinc (787°), tin (450°) and lead (621°) are about the only ones you can melt at such low temps. And only tin can be melted reliably at a vent. The other two are going to be rare to find vents hot enough

 

[Navarro_Refugee]

There's also issues of impurities and pressure to consider when talking about smelting metal. Smelting in salt water isn't going to do anything good for the quality of your metal and the increased pressure at the bottom of the ocean is going to drive up the melting point, which is going to make the task of melting it with the limited heat of the hydro-thermal vents that much harder.

 

[Tasrill]

There are plenty of ways to process food that don't require fire. Even good old fashioned 'beat it with a rock till it is soft' is going to let you spend less energy digesting the food. The next step up the ladder from that would be chemically treating the food or fermenting it which also can happen underwater. Heat is easy mode for making things easier to eat but it isn't the only way that was used by our own hunter gatherer ancestors.

 

[Akhera]

Another thing to take into account is that smelting isn't just about temperature. There's also a chemical reaction that has to occur. In case of iron ore it has to react with carbon monoxide, which on dry land furnaces conveniently comes from burning the coal that you're heating it with.

 

[Heliostorm]

1: Part of my asking this question is for the possibility of life in underground oceans like Europa or Enceladus, which come to think of it would have even higher pressures given the indicated depths. Or does the lower gravity cancel that out somewhat?

2: Wait if they're that shortlived how do creatures like giant tube worms survive?

3: Would it be possible to build a device that could concentrate the heat until it reaches smelting levels?

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The juvenile stage of tube worms is mobile and follows currents to reach new thermal vents. The average lifespan of a hydrothermal vent is somewhere between years and decades.


"Concentrating heat" is the wrong way to think about it. "Concentrating heat" means moving heat up a gradient, which requires work. This means building an engine, one fueled by the thermal gradient of the vent itself. There is no reason why one cannot build say, an electric furnace powered by the hydrothermal vent to achieve temperatures capable of smelting metals. The caveat here is, obviously, such technology requires one to already have smelted metals. It is impossible to build such advanced machinery without metal.

But really, this is only the beginning of the problems of hydrothermal-vent civilizations. There just isn't enough energy available from vents to sustain a large enough biosphere capable of sustaining a civilized species. Energy and nutrition are incredibly hard to get at the bottom of the ocean and species have to be adapted for efficient usages of both, and large brains are not along that evolutionary path. There is an enormous selection pressure against developing the intellect necessary to even comprehend the concept of cooking food.

Just to put the numbers out there, the Earth receives 173,000 TW from the sun. The total energy from all Earth's geological activity only amounts to 43 TW. So you're attempting to evolve a human brain on something like 1/4000th of the energy budget. Even if life could use that energy with 100% efficiency (when really it's more like 0.1%), it'd still be less than the amount of energy used by the solar biosphere.

 

[Tasrill]

The juvenile stage of tube worms is mobile and follows currents to reach new thermal vents. The average lifespan of a hydrothermal vent is somewhere between years and decades.


"Concentrating heat" is the wrong way to think about it. "Concentrating heat" means moving heat up a gradient, which requires work. This means building an engine, one fueled by the thermal gradient of the vent itself. There is no reason why one cannot build say, an electric furnace powered by the hydrothermal vent to achieve temperatures capable of smelting metals. The caveat here is, obviously, such technology requires one to already have smelted metals. It is impossible to build such advanced machinery without metal.

But really, this is only the beginning of the problems of hydrothermal-vent civilizations. There just isn't enough energy available from vents to sustain a large enough biosphere capable of sustaining a civilized species. Energy and nutrition are incredibly hard to get at the bottom of the ocean and species have to be adapted for efficient usages of both, and large brains are not along that evolutionary path. There is an enormous selection pressure against developing the intellect necessary to even comprehend the concept of cooking food.

Just to put the numbers out there, the Earth receives 173,000 TW from the sun. The total energy from all Earth's geological activity only amounts to 43 TW. So you're attempting to evolve a human brain on something like 1/4000th of the energy budget. Even if life could use that energy with 100% efficiency (when really it's more like 0.1%), it'd still be less than the amount of energy used by the solar biosphere.

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The problem here is that as far as I can tell you aren't counting the chemical energy that is unlocked through geological activity and therefore are massively underestimating the amount of energy around. Here is a chart of total biomass that goes into before the oxygenation event.



Photosynthesis is generally thought of to have first evolved 3.4 ish billion years ago so it isn't a perfect chart but for earth it is looking more in the 150x better than the 4000x better. As a person who can't photosynthesis from a long line of creatures that can't the bigger issue is how does one evolve mobile, multicellular life without some kind of turbo juice like oxygen.

 

[Heliostorm]

The problem here is that as far as I can tell you aren't counting the chemical energy that is unlocked through geological activity and therefore are massively underestimating the amount of energy around. Here is a chart of total biomass that goes into before the oxygenation event.



Photosynthesis is generally thought of to have first evolved 3.4 ish billion years ago so it isn't a perfect chart but for earth it is looking more in the 150x better than the 4000x better. As a person who can't photosynthesis from a long line of creatures that can't the bigger issue is how does one evolve mobile, multicellular life without some kind of turbo juice like oxygen.

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The 99.9% of energy the Earth gets from the sun that isn't directly absorbed by life is nevertheless absolutely essential for the biosphere. Weather, climate, ocean currents, a livable ambient temperature, these are all driven by solar energy and all are as equally important for creating a complex biosphere as the energy absorbed by photosynthesis. You need all that extra "free" energy just to keep the planet from freezing over.

 

[Tasrill]

The 99.9% of energy the Earth gets from the sun that isn't directly absorbed by life is nevertheless absolutely essential for the biosphere. Weather, climate, ocean currents, a livable ambient temperature, these are all driven by solar energy and all are as equally important for creating a complex biosphere as the energy absorbed by photosynthesis. You need all that extra "free" energy just to keep the planet from freezing over.

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Freezing over isn't a problem as long as you can have a reasonably sized layer of none frozen water. Earth has gone through multiple snowball earth events where all to nearly all was frozen. Underground oceans are in the end still oceans and livable is a very broad range.

 

[Heliostorm]

Freezing over isn't a problem as long as you can have a reasonably sized layer of none frozen water. Earth has gone through multiple snowball earth events where all to nearly all was frozen. Underground oceans are in the end still oceans and livable is a very broad range.

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That changes nothing. You invariably need to inject large amounts of heat into the oceans or else they will eventually freeze all the way down to the bottom. Layers of ice can help this to an extent by insulation but it doesn't change the inevitable fact that any system will need to expend a large portion of its energy to maintain a survivable environment for life. Earth's biomass pre-photosynthesis would not have been nearly as high without solar energy.

 

[Tasrill]

That changes nothing. You invariably need to inject large amounts of heat into the oceans or else they will eventually freeze all the way down to the bottom. Layers of ice can help this to an extent by insulation but it doesn't change the inevitable fact that any system will need to expend a large portion of its energy to maintain a survivable environment for life. Earth's biomass pre-photosynthesis would not have been nearly as high without solar energy.

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Yes and heat energy and chemical energy are not the same thing and they are not interchangeable. That is the point I was making not that having more living space doesn't relate to more biomass. Specifically I was pointing out that you are ignoring a large and important source of energy which makes your calculations incorrect.

 

[Heliostorm]

Yes and heat energy and chemical energy are not the same thing and they are not interchangeable. That is the point I was making not that having more living space doesn't relate to more biomass. Specifically I was pointing out that you are ignoring a large and important source of energy which makes your calculations incorrect.

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If you want to present evidence that there is comparatively more chemical energy available at the bottom of the oceans than in the rest of the world, be my guest. But nothing you've mentioned actually supports that position.

 

[firefossil]

That changes nothing. You invariably need to inject large amounts of heat into the oceans or else they will eventually freeze all the way down to the bottom. Layers of ice can help this to an extent by insulation but it doesn't change the inevitable fact that any system will need to expend a large portion of its energy to maintain a survivable environment for life. Earth's biomass pre-photosynthesis would not have been nearly as high without solar energy.

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Various moons around gas giants have maintained liquid water oceans despite getting zero sunlight. My assumption is that much of that is due to surface ice acting as an insulator. They also get heat from tidal forces, which doesn't let you cook things but does keep the ocean an ocean rather than an iceball:

The scientists then ran experiments in the lab to determine how such silica particles came to be. With the particles' particular makeup and size distribution, they could only have formed under very specific circumstances, the study authors found, determining that the silica particles must have formed in water that had less than 4% salinity and that was slightly alkaline (with a pH of about 8.5 to 10.5) and at temperatures of at least 90 degrees Celsius (roughly 190 degrees Fahrenheit).

The heat was likely being generated in part by tidal forces as Saturn's gravity kneads its icy moon. (The tidal forces are also probably what open the cracks in its surface that vent the water vapor into space.)

Somewhere inside the icy body, there was hydrothermal activity – salty warm water interacting with rocks. It's the kind of environment that, on Earth, is very friendly to life.

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As the above article notes, silicon dioxide particles believed to have originated from Enceladus would require temperatures close to boiling to have formed, which implies the liquid ocean probably has hydrothermals in additional to tidal forces. Overall though I'd agree that the various underground oceans can't support sapient or quite possibly even just complex life, due to the limited energy and resources available. That said I do wonder... what if you had a moon like Io that's getting practically pulled apart by larger moons and the gas giant it orbits, but has a composition more akin to iceballs like Europa?

Compositional mapping and Io's high density suggest that Io contains little to no water, though small pockets of water ice or hydrated minerals have been tentatively identified, most notably on the northwest flank of the mountain Gish Bar Mons.[83]​ Io has the least amount of water of any known body in the Solar System.[84]​ This lack of water is likely due to Jupiter being hot enough early in the evolution of the Solar System to drive off volatile materials like water in the vicinity of Io, but not hot enough to do so farther out.[85]​

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This seems to imply that the factors that give Io so much tidal heating also probably denied it access to water (and other key ingredients for life like nitrogen and carbon dioxide) however it also indicates that the loss was because of Jupiter being hot not tidal forces so it isn't necessarily a dealbreaker.

So if could you end up with a tidally churned volcanic underground ocean world would that be able to support more advanced life? I mean you talk about sunlight giving more energy, but outside of climate/weather/temperature (which isn't applicable to underground oceans anyways) I'm pretty sure that life is only using a small fraction of the sunlight that hits anyways.

 

[Heliostorm]

Various moons around gas giants have maintained liquid water oceans despite getting zero sunlight. My assumption is that much of that is due to surface ice acting as an insulator. They also get heat from tidal forces, which doesn't let you cook things but does keep the ocean an ocean rather than an iceball:

As the above article notes, silicon dioxide particles believed to have originated from Enceladus would require temperatures close to boiling to have formed, which implies the liquid ocean probably has hydrothermals in additional to tidal forces. Overall though I'd agree that the various underground oceans can't support sapient or quite possibly even just complex life, due to the limited energy and resources available. That said I do wonder... what if you had a moon like Io that's getting practically pulled apart by larger moons and the gas giant it orbits, but has a composition more akin to iceballs like Europa?

This seems to imply that the factors that give Io so much tidal heating also probably denied it access to water (and other key ingredients for life like nitrogen and carbon dioxide) however it also indicates that the loss was because of Jupiter being hot not tidal forces so it isn't necessarily a dealbreaker.

So if could you end up with a tidally churned volcanic underground ocean world would that be able to support more advanced life? I mean you talk about sunlight giving more energy, but outside of climate/weather/temperature (which isn't applicable to underground oceans anyways) I'm pretty sure that life is only using a small fraction of the sunlight that hits anyways.

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*shrug* Maybe, maybe not. It's kind of like the question on whether or not silicon life is possible--we can come up with a long list of reasons why it would be harder than carbon-based life, but in the end we can't say for sure. Maybe there's a goldilocks zone between not enough activity making it too cold and not enough nutrients and energy, and too much activity making it too hot and too toxic for any kind of primitive life. Or maybe there isn't.


It's not impossible to imagine that hydrothermal vents on other worlds could be hot enough to melt metal either, although at that point it wouldn't be anything like the vents we know and I'm hard-pressed to imagine how primitive aliens could survive close enough to smelt anything.

 

[firefossil]

*shrug* Maybe, maybe not. It's kind of like the question on whether or not silicon life is possible--we can come up with a long list of reasons why it would be harder than carbon-based life, but in the end we can't say for sure. Maybe there's a goldilocks zone between not enough activity making it too cold and not enough nutrients and energy, and too much activity making it too hot and too toxic for any kind of primitive life. Or maybe there isn't.

It's not impossible to imagine that hydrothermal vents on other worlds could be hot enough to melt metal either, although at that point it wouldn't be anything like the vents we know and I'm hard-pressed to imagine how primitive aliens could survive close enough to smelt anything.

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TBH in some ways extreme tidal activity would seem like a good thing. Hydrothermal vents are believed by some to be where life evolved on Earth in the first place due to the dynamic conditions (water and melted minerals mixed in a heat environment) present there, and even on Earth we've seen extremophiles survive boiling temperatures or toxic mineral laden waters, presumably life there would be more heat and mineral tolerant than most.

Hmm from what I understand there are photosynthetic pigments that can draw power from red or even outright infrared thermal heat, and it wouldn't surprise me if something further into the infrared is possible but just had no reason to develop. Ergo you might end up with a sort of reversed biosphere in which bacteria and kelp power themselves via the red light and thermal heat coming from the glowing hot ocean floor.

As for smelting, yeah the issue is you need need not only the high temperature needed to melt, but also for nearby temperatures to be tolerable enough that space octopus with a pointy rock or whatever can dangle the ore without burning up.

 

[Heliostorm]

TBH in some ways extreme tidal activity would seem like a good thing. Hydrothermal vents are believed by some to be where life evolved on Earth in the first place due to the dynamic conditions (water and melted minerals mixed in a heat environment) present there, and even on Earth we've seen extremophiles survive boiling temperatures or toxic mineral laden waters, presumably life there would be more heat and mineral tolerant than most.

Hmm from what I understand there are photosynthetic pigments that can draw power from red or even outright infrared thermal heat, and it wouldn't surprise me if something further into the infrared is possible but just had no reason to develop. Ergo you might end up with a sort of reversed biosphere in which bacteria and kelp power themselves via the red light and thermal heat coming from the glowing hot ocean floor.

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Infrared transmits very poorly through water, so that's unlikely. There exist no thermosynthetic organisms in nature that we know of, so this seems even less likely.


Water is most transparent to blue light, which is of course, why it looks blue.

 

[firefossil]

Infrared transmits very poorly through water, so that's unlikely. There exist no thermosynthetic organisms in nature that we know of, so this seems even less likely.


Water is most transparent to blue light, which is of course, why it looks blue.

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Well the current confirmed record is this:

The newfound pigment, dubbed chlorophyll f, absorbs light most efficiently at a wavelength around 706 nanometers, just beyond the red end of the visible spectrum, researchers report online August 19 in Science. This unique absorbance appears to occur thanks to a chemical decoration known as a formyl group on the chlorophyll's carbon number two. That chemical tweak probably allows the algaelike organism that makes chlorophyll f to conduct photosynthesis while living beneath other photosynthesizers that capture all the other usable light.

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Which would make the algae in question be thermosynthetic, albeit only by the barest technicality. Getting further is hard. Plants use visible light because ultraviolet is too intense and damages them but infrared isn't intense enough, there are tricks to bypass but not practical for life to develop most likely.

That said your chart is unclear to me, I'm not sure how to read the absorption. What kind of rate of loss are we talking about at the edge of red/infrared?

 

[Heliostorm]

Well the current confirmed record is this:

Which would make the algae in question be thermosynthetic, albeit only by the barest technicality. Getting further is hard. Plants use visible light because ultraviolet is too intense and damages them but infrared isn't intense enough, there are tricks to bypass but not practical for life to develop most likely.

That said your chart is unclear to me, I'm not sure how to read the absorption. What kind of rate of loss are we talking about at the edge of red/infrared?

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That's still photosynthesis. Infrared light isn't really heat in the physics sense.

The axis on the left is the attentuation coefficient, it's basically out of how many photons will 1 photon make it through 1 m of material.

Lava/magma's emission peaks around the near-mid-IR range so the red-near absorption would be terribly inefficient.