I have a post-apocalyptic world where some intelligent animals become the new major world-controlling species. In particular, some new/evolved species of Cuttlefish and Octopi are beginning to fill the world-dominating niche we humans currently enjoy. We know (real-world) cephalopods are really smart, and can even open jars while stuck on the inside: this story is just assuming those creatures gain more intelligence and humans are more-or-less removed from the picture.

These cephalopods can't do everything on their own, though, and becoming the dominant species/society requires some tool use. I just can't seem to justify getting my super-smart cephalopods out of the stone age. Iron rusts and corrodes in the ocean. Bronze requires alloying, which generally requires fires. Also, the ocean has a tendency to corrode/dissolve metals.

How will I get my octopi/cuttlefish beyond stone-age technology? More specifically, what metals can these cephalopods develop and use in the ocean?

You may assume:

  • real-world values for everything except for the cephalopod intelligence
  • these smart cephalopods are about as intelligent as humans.
  • You can safely assume an octopus can use their tentacles for the same purposes we use our hands.
  • Plastics, from humans, are still around but not being made. Computers, electric grids, and other remnants of human civilization are out-of-reach (and sight) or decayed beyond usefulness.
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    $\begingroup$ Related - How would an aquatic civilisation forge tools?. $\endgroup$ – Samuel Dec 1 '15 at 0:44
  • $\begingroup$ Octopodes (sorry ;)) $\endgroup$ – fgysin reinstate Monica Dec 2 '15 at 9:42
  • $\begingroup$ Also, there are ways of getting fire (or at least temperatures hot enough to forge bronze) under water, namely volcanic vents. They would be difficult to utilize, but nothing worth having is easy. ;) $\endgroup$ – Draco18s no longer trusts SE Dec 2 '15 at 17:19
  • $\begingroup$ If Cephalopods evolve into more intelligent creatures with human level intelligence, is there any reason they couldn't also adapt to life outside of water? Haven't you ever heard of the Pacific Northwest Tree Octopus? $\endgroup$ – GrandmasterB Dec 3 '15 at 5:59
  • $\begingroup$ @GrandmasterB No, in fact, I've never heard of it. $\endgroup$ – PipperChip Dec 3 '15 at 6:16

You seem to be assuming that they would follow the same technology path as humans. But what if that's not the case? Necessity is the mother of invention, and your cephalopods really need useful non-metallic materials.

Humans went with metals because they're relatively easy to obtain and work. An underwater civilization might look at other options early in on because of those difficulties you mention. Maybe they'll play around with ceramics, learning how to make useful, water-resistant materials thousands of years earlier on the tech path than we did. Maybe they'll learn how to mess with carbon allotropes, using graphene cabling and synthesized diamond.

Another alternative would be biological sources. Humans do this a bit, but what a civilization that stumbled on it early on might find uses and efficiencies far beyond what we've accomplished.

In either case metals will still be used where they're useful, but it will be rare, and they'll probably use their other technologies to jump-start their tech curve so they can create better/more useful alloys.

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    $\begingroup$ And what about shaping things as they grow? Coral would be a good prospect. Some of the stony corals are pretty tough. $\endgroup$ – Francine DeGrood Taylor Dec 1 '15 at 19:54

I would tend to agree with Dan's answer, biological answers might be the most useful for them. Silicon and Carbon are very useful for many things, and they will have plenty of silicon available. Maybe using biologic secretions to bind the sand together, there are already some that do that. Homes would likely be very biological, as in living coral, shaped and tended.

One last thing, gold is mostly immune from salt water, it also happens to be very conductive so there are many things this might lead to.

I think chemistry would be a huge area of interest to any sea born intelligence, much earlier than humans, since they live in a chemical rich soup, and all kinds of animals add their chemicals to the mix all the time. Chemistry would be the main path to survival, not bronze age tools.

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  • $\begingroup$ One of the challenges of being a chemist in an underwater setting would be how to work with the chemicals without ingesting them or otherwise coming into contact with them. Even if a substance is mostly not water soluble, salt water is fairly caustic and might leech off the surface of the chemical. How would they keep their substances isolated from their living environment? Even if they built containers, those containers would have to remain sealed most of the time. How would they safely exchange liquid or semi-solid elements between containers? $\endgroup$ – Francine DeGrood Taylor Dec 1 '15 at 19:59
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    $\begingroup$ @FrancineDeGroodTaylor like all good alchemists, trial and error, self poisoning and missing appendages. $\endgroup$ – bowlturner Dec 1 '15 at 20:06
  • $\begingroup$ @bowlturner...lol. Without the advantage of gravity, however. Except in the case of heavy chemical components. It would be a little like having to work with only heavier-than-air gasses. Not impossible, but more complicated. $\endgroup$ – Francine DeGrood Taylor Dec 1 '15 at 21:50

I agree with the other two answers. They would develop technology on a different path, and much of that would be conjecture. Perhaps it would make it easier to avoid explaining their technological path at all (we know fairly little of human history, and cephalopods would have had trouble preserving any writings underwater for great lengths of time).

However, heat sources seem to be fairly important in much of our technology. Here are some ideas for heat sources:

  • My best guess for heat would be that they discover underwater oil reserves, which they then burn at the surface of the ocean in order to create ceramics and such.
  • Geothermal vents underwater
  • Deep sea volcanic areas

Heat aside, some possible manufacturing methods: - Epoxy-like glues that harden even underwater - Building above-water vessels, tunnels, reverse "docks" and so forth, to allow access to land-based technology techniques. - Putting air back in water, and filtering water, would be easier for them than for us to put air below water. Land travel would probably have come into play far earlier in their civilization, though limited by glass-making techniques. - Taming and training animals to do dangerous above-ground work, to reasonable extents.

You might also make an allowance that cephalopods evolved the ability to sustain themselves above water for long enough periods to do simple tasks, like start a fire, collect a bit of firewood, etc.

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  • $\begingroup$ I love the idea of a cephalopod "reverse-submarine," with an oxygenator on top to keep the water breathable. Deserts would be especially dangerous to explore, as you'd need surface water to refill the water tank periodically. $\endgroup$ – user243 Dec 2 '15 at 12:47
  • $\begingroup$ @user243 refilling the water tank: maybe, but perhaps you could filter the water adequately to extend the journey before unfilterable junk becomes toxic. Also, I imagine they could invent the rough equivalent of a bathroom to keep water cleaner. $\endgroup$ – Kimball Robinson Jul 7 at 17:41

Intelligent Cephalopods will figure out how to make dry rooms under water before too long, solving many of the problems holding them back.

Initially the rooms might be caves where the air is brought in manually (tentacually?), but the next step will be artificial structures just below the surface with transparent plastic sheet roofs and sea weed to produce oxygen bubbles.

I would imagine the Octopi would drape themselves in kelp to keep their skin moist and oxygenated and use one tentacle to hold a plastic bag over their gill openings, allowing them to stay in the dry room for up to an hour or so. The same strategy would allow them limited exploration of the land.

Plastic bags and sheets would be highly valuable and finding more of them a major driver to explore the land further.

On land, they would eventually encounter handy deposits of gold, titanium and other long lasting metals left behind by humanity. While it's unlikely they would do more than hammer them into shape, it would still allow for new tools.

As said in the other answers, they are much more likely to develop biotechnology than metallurgy, using bred sea creatures for food, construction, transport, war and more.

  • Who needs a steel sword when you can ride a War Shark into battle?
  • Who needs iron farm tools or wheels set in iron bands when "farming" is as simple as putting up nets when the tide goes out?

The primary uses for fire were warmth, light in the darkness and to make tough food more digestible. The Cephalopods don't need it for any of that. They are comfortable at seawater temperatures, can see very well or even make their own light and eat sushi all day every day.

Until the industrial revolution, iron was mostly useful for those purposes: enabling farming and warfare. At that point, steel's resistance to heat and pressure enabled humans to develop steam and combustion engines.

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Since the idea that the Cephalopods will develop some sort of biotechnological infrastructure (based on precipitating calcium and salts out of the water, much the way shells are made), I will try to suggest how they might become inheritors of the land as well.

Since Cephalopods will be working in the shallows to gather food, lurk in kelp and seaweed beds etc., it isn't a big stretch to imagine that they will eventually evolve to become amphibious and able to operate on land. Since they prefer water to land, they will have incentives to dig canals, lagoons and other artificial structures in order to live comfortably farther inland, away from the ocean yet still close to the water. For this they will need to start using tools.

At first, grabbing a suitable stick to scrape away at the mud will do, and eventually they will discover that rocks can also be used to chip away at hard obstructions, or smack open a tasty morsel that is otherwise too tough for their beak to open. From there, they can easily replicate the achievements of our own Neolithic Ancestors, at least up to the point they discover fire.

Since they are amphibious, how they will deal with fire is an interesting question. Fire is going to be far more dangerous to them than it is to us, and in their semi aquatic environments, building and maintaining fire may be difficult to impossible. Without fire, however, they will be unable to move to metallurgy or the various technologies that metals make possible (including energy, electricity and so on). It is hard to see how they can move past the neolithic without mastering the technology of fire first, so at this point they might either stall and remain in the stone age forever, or make some sort of conceptual leap and master fire. (A bigger stretch would be to have another bout of evolution making the Cephalopods fully land dwelling creatures with leathery skin like reptiles and the ability to either hatch eggs or carry their young to term).

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