I'm trying to decide whether it would be possible for super-intelligent cephalopods to use underwater lava vents to refine metals. Would make a fun SF premise, but I take your point.

> From a technological point of view, the main distinctive feature of humans has not been the use of tools, which is relatively widespread among animals, but the control of fire.

> The control of fire is what has enabled humans to […]

… on Earth with an iron-nickel core and an oxygen rich atmosphere, with easy access to vasts of low energy density organic material (dead trees) and higher density energy source (coal). Either of the two can be literally picked up from the surface, which was even more important for ancient civilisations.

But mastery of combustion is just one successful path, not a universal prerequisite. What matters is access to controllable high energy densities and redox chemistry that can extract, shape and join structural and conductive materials. On many plausible worlds those needs could be met without fire. Fir instance:

  1. Native metals and cold working – worlds rich in native copper, silver or gold from hydrothermal deposition or reducing atmospheres allow metal use with no smelting. Cold hammering, annealing on warm geothermal surfaces, and pressure-sintering can produce wire, sheet and simple tools. Meteoric iron is another route to early ironwork by cold forging.

  2. Electrochemical extraction at ambient temperatures – acidic or chloride brines can leach Cu²⁺, Ag⁺, Zn²⁺ and similar ions that can be plated onto seed cathodes. Electricity could come from: a) galvanic piles built from naturally dissimilar minerals in a brine; b) tidal, wind or river generators driven by simple turbines; c) lightning harvesting into capacitors, then steady discharge into plating cells. This is essentially solvent-extraction and electrowinning without a firebox.

  3. Solar furnaces without flames – on oxygen-less or thin-oxygen worlds with intense sun, arrays of polished stone, mica sheets or vitrified sand mirrors can reach smelting temperatures. Early optics need not be metallic – glazed ceramics and transparent minerals suffice – so a civilisation could jump straight to photothermal metallurgy.

  4. Non-combustive chemical heat – highly exothermic mixtures – thermite-class reactions and metal sulphide or halide reductions – release smelting-grade heat once initiated. On halogen-rich worlds, fluorides or chlorides could be reduced by hydrogen or metals to yield both heat and purified product. This is chemistry as furnace.

  5. Under-ice or ocean worlds – combustion may be impossible, yet hydrothermal chimneys deposit native metals and sulphides. Technology could develop around: a) ceramic and glassworking using geothermal heat; b) galvanic circuits using sulphide–metal couples in seawater for plating; c) arc heating from captured lightning or magnetospheric induction to melt and weld underwater.

  6. Biological ore upgrading and metal precipitation – an interesting idea to entertain as microbial consortia already leach copper and gold on Earth at ambient temperatures. Projecting further, an alien biosphere could be domesticated to: a) acidify heaps and liberate ions from ore; b) reduce and precipitate metals onto templates for near-net-shape parts; c) grow conductive biomaterials that substitute for early copper wiring. Biometallurgy can start well below 100 °C and scale industrially.

We should also not entirely dismiss a possibility of material alternatives that postpone, or even replace, metallurgy – advanced ceramics, glasses, cements, laminated woods and fibre composites can carry a civilisation far – structural engineering, containers, even turbines and high-temperature reactors. Conductive paths can begin with graphite, sulphides and native copper; semiconducting minerals such as galena enable primitive electronics. Metallurgy may arrive later or remain niche.

None of the above is outside the constructs of the laws of physics and chemistry, and, most assuredly, the suggested alternatives are not crack pot theories or hard code science fiction – provided the local environment has favourable conditions that meet one or multiple criteria. Even more so if an alien civilisation had an earlier head start – modern humans have only been around for 200 thousand years circa (we won't include the earlier hominid forms), and if another civilisation could have started advancing «just» 1 billion years earlier, they would have had a luxury of progressing steadily even if at a slower pace.

To sum it up, none of the above requires fire for a hypothetical extraterristrial civilisation to advance. Fire was the proverbial low-hanging fruit and the path of the least resistance, so the early humans enthusiastically adopted it given that the terrestrial environment favoured and «encouraged» the use of fire, so to speak.