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I'm sketching a story about a rogue Earth (that is, Earth got flung out of the solar system) and how humanity could survive. One of the main problems is food. Hydroponic farms with grow lights are one way to generate food in a post-sun world, but these use a lot of resources.

So I was considering if it would be possible to tap a natural source for food. I found an article from PNAS about the carbon productivity from hydrothermal vents, and one in particular (Crab Spa) may reach up to 9,300 kilograms of carbon per square meter per year (9.3 kgm2yr-1).

I tried to find similar data for forests - best I could find so far is a short page from NASA measuring primary productivity from space. I see that the most productive forests have a net productivity of carbon fixation in the range of 6.5 grams of carbon per square meter per day, which is about 2.37 kgm2yr-1.

With my limited understanding of biology I am interpreting this as to mean that an hydrothermal vent can produces approximately four times more biomass per area than a patch of rain forest on the same timespan. I wonder if a post-apocalyptic society could harvest the vents for food in a sustainable form, then? Like sending a ROV to catch shrimp or something like that.

If this is possible, is there a way to measure how many people could live off a square meter of hydrothermal vent?

P.s.: this is really not the only food source people will have. There will be underground farms with grow lights, in this question I'm wondering if it would be possible to harvest from hydrothermal vents so as to reduce the pressure on those farms.

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    $\begingroup$ I should point out that hydroponic farms wouldn't solve a lack of sunlight, as hydroponics is just a way to grow plants without soil. You'd need an artificial light source, like grow lights (en.wikipedia.org/wiki/Grow_light). $\endgroup$
    – Pitto
    Dec 7, 2020 at 21:24
  • $\begingroup$ @Pitto you're right - I'll edit the question. $\endgroup$ Dec 7, 2020 at 21:28
  • $\begingroup$ I'll be interested to see the answers to this question, it's a lot more complex than it seems. As a rouge planet, the ability to keep the entirety of the oceans unfrozen will be impossible. That means the hydrothermal vents are warming pockets of liquid entrapped in ice. That liquid will lack all kinds of usually necessary things, and I suspect both the oxygen and the carbon cycles will be very compromised (especially since the vents are venting, among other things, sulfur). It's more believable that everything would die and the areas become sterile... but... (*continued*) $\endgroup$
    – JBH
    Dec 7, 2020 at 21:52
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    $\begingroup$ note hydrpther,mal vents take up very small areas, so while they may be more productive pr sq meter but there are far less square meters. $\endgroup$
    – John
    Dec 7, 2020 at 22:02
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    $\begingroup$ Do we have data concerning how much of the Earth's core is contributing to surface warming? Very little. But soil and rock are not good conductors of heat and the temperature increases by roughly 25-30 degrees C per km you go down and that's away from active plate boundaries. Extensive amounts of water would probably continue to exist for a great deal of time. $\endgroup$
    – Slarty
    Dec 7, 2020 at 23:07

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Yes, but it will mostly not be worth it.

The energy source that hydrothermal vents supply is in the form of chemical compounds such as hydrogen sulfide, that is then consumed by anaerobic microbes. These are utterly inedible by us, can eventually support creatures (such as the mentioned shrimp) that can serve as food source. However this several-layer stepdown of predation is not an efficient way to grow food. The vent may support 9.3 kg per meter per year of growth, but the harvest of shrimp from this will be a magnitude or two lower, in the same way that sunlight supports a lot of grass growth but the mass of beefburgers per square meter of grassland is distressingly low.

For your Rogue Earth scenario, I would be much more interested in the warm water that comes from the vent. This will keep a large region of the water around it at elevated temperatures.

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If you could prevent the vent itself from freezing, the heat of the earth would not run out for many, many, many lifetimes over. This is because the earth is heated by radioactive decay and immense pressure.

You could possibly survive a few years on lichens.

TL;DR

Not for long. No hydroponics. UNLESS you could generate electricity. Then you may have a slim chance.

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