In a question I saw on here a while back, somebody said that the development of a sapient, technologically progressing species requires fire, and thus such a phenomenon could not occur under water.

However, geothermal vents can become quite hot, and so could it be possible for an underwater species to use that for purposes that would normally require a fire, such as cooking meat and melting metal and such?

If such conditions are not possible on earth, could a situation allow this on other planets? And what would be the effects of the required changes?

Thank you!


5 Answers 5


They key thing determining what you can do with a geothermal vent is how hot it gets. The hottest subsea vents on Earth measure around 410 °C at the surface; you might be able to get a bit hotter though clever plumbing or isolating the water supply.

Now, what can you do with 400-500° water?

  • Cooking. Virtually all cooking takes place at lower temperatures, so there's no problem here. (In fact, Fishing Cone Geyser in Yellowstone was used for cooking fresh-caught fish).
  • Casting metal. Out of the classic metals, tin, zinc, and lead all have melting points below 500°C. The actual process would be a bit tricky, as you need to isolate the metal and the mold from water to prevent overly-quick cooling; if you're using a shallow vent, you also need to worry about steam explosions.

What you can't do:

  • Smelt the metal in the first place. Tin, zinc, and lead all are smelted by heating the appropriate oxide to temperatures in excess of 1000°C in the presence of a reducing agent.
  • 1
    $\begingroup$ you have a bigger problem, water is not an insulator like air, so the water around your forge will be more than hot enough to boil your mermen alive. $\endgroup$
    – John
    Feb 18, 2021 at 14:44
  • 1
    $\begingroup$ @John, for something like metal casting (or cooking fish), you can enclose the raw materials in a suitable water-tight container (eg. clay), and lower it into the vent on a heat-resistant line. $\endgroup$
    – Mark
    Feb 20, 2021 at 1:38

Just to widen the scope a bit, in regards to "the development of a sapient, technologically progressing species requires fire, and thus such a phenomenon could not occur under water.", that statement shows a distinct lack of imagination and critical thought. perhaps not a "technologically progressing species" in the same way WE progress, but just a moments thought can give many alternatives. for example, where we progressed thru fire and metallurgy, the hypothetical aquatics may progress thru biological manipulation and electricity. for example, suppose some genius noticed that the shocks give off by an electric eel analogue are transmitted thru a certain species of seaweed analogue, and had the idea of trapping a electric eel and constructing a barrier of said conductive seaweed, where he could connect the eel to the barrier and induce it to give off a shock to ward away a predator. is this not considered "technologically progressing" ? it could lead to genetic manipulation via breeding both eels and seaweed, and looking for other such things like finding and improving a biological source of stronger materials, perhaps based on calcium, silicon, etc to make weapons and devices from. Our own science is just beginning to explore making materials from, for example, inducing bacteria and other "living" organisms to grow them how we want them.


The biggest problem with the geothermal vents is that they're located deep in the abyssopelagic zones.

While it might be tempting to view the ocean as the monolithic volume that your species can travel freely in any of the six directions, it's not the case, the water there is nearly devoid of oxygen and will kill anyone who's unable to get away quickly, and then there are the pressure issues as well. It's quite literally analogous to trying to climb Mt. Everest with prehistoric tools, with the exception that you're absolutely blind during the whole journey.

Abyssopelagic zone is more or less isolated from the sunny upper layers of the oceans, so apart of the "how to survive down there" problem, your species will have the "how to learn that there is something of use to give us the reason to venture there" problem as well.


Apart from the metals referred to in the original response (lead, tin and zinc - and lead is toxic) there's no metals that could be reduced at the temperatures and in the environment described. However you might (and I do stress might) with the appropriate technical knowledge possibly use or substitute certain polymers and clay/ceramics to make tools etc. Even this though has strict limits on utility re; what you can produce when limited to geothermal springs as your one and only energy source.

An aquatic culture could become adept at selective breeding and aquaculture etc but as long as they are fully aquatic and not semi-aquatic they are pretty much doomed to pre-industrial revolution technology levels. Which does not of course stop them advancing in other areas like mathematics and the arts that are not reliant on ongoing advances in material science.

So while they can 'advance' in some fields as far as technology goes they will have hit a plateau beyond which they cannot advance without leaving the ocean.


This question seems to be doing two things:

  1. asking for confirmation that fire is required
  2. and, based on the assumption that it is, asking if ocean vents could fill that requirement

This answers purpose is to point out that fire, (or high general heat), MAY NOT BE REQUIRED for development of technology in an aquatic environment. AND I am providing a different solution.

First: NO it appears fire is NOT required for technological advancement.

I am recycling another answer to a similar question to explain: this question*.

*(as in I am almost completely quoting the answer I added to that question).

However it provides an alternative to the requirement of needing fire to smelt metals... it would require the race to
- experiment a lot,
- possibly find solvents for metals (heat from vents may help here)
- and likely methods of isolating the desired metals

...I suspect it would be possible for a bioelectric race, to learn advanced forms of electroplating & electroforming.

My limited understanding of electroplating is:

Dissolve a metal Develop a 'mandrel' in the desired shape Utilize an electric current which, in some way, bonds the metal to the mandrel (not exactly sure on the details of how...) All of the above steps seem likely to be possible & even possibly easier, in an aquatic environment.

Electroforming is actually even more interesting, in that it is used to create highly detailed as well as much thicker products.

Electroforming could be used to actually produce things such as knives, swords, etc... out of metal, (not just a coating of metal on something else more easily formed). Additionally electroforming can be VERY accurate in reproducing highly detailed forms/mandrels, even, if I understand correctly, on the nano scale (the scale of the transistors our current computer chips are measured in). This would very much support the idea of making computer circuits in a similar form as our PCBs (Printed Circuit Boards)... to go with your other post on that topic (and what got you thinking about this one).

Hopefully the above is helpful for you when developing your race. I highly recommend reading this answer from Culyx on this very topic.

  • $\begingroup$ Does the heat of the hydrothermal vents contribute to this process? $\endgroup$
    – Mark
    Feb 18, 2021 at 4:22
  • $\begingroup$ @Mark to the best of my limited knowledge it could, (as solvents tend to be more reactive when heated). However that was really not my point and I'll make my pont more clear in this answer. $\endgroup$
    – MER
    Feb 20, 2021 at 1:20
  • $\begingroup$ To those who downvoted, I'm curious, what did you see as inappropriate for the question? I felt it was a valid answer to a good question (or I wouldn't have left it) if you disagree please tell me why. OR Do you believe this is disingenuous because I quoted myself instead of re-typing? Or you don't like it when people promote someone else's answers to a different question? Anyway would be interested to know, whatever the reasons, (maybe there's something obvious I missed??) $\endgroup$
    – MER
    Jun 18, 2021 at 22:32

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .