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In many Sci Fi and Fantasy worlds, the deserts are filled with giant megafauna that swim through dunes of loose sand. The issue with this depiction of course is not just the size of said sand swimmers, but of where the energy needed for such giants come from.

If we look at the real world, deserts do not have a any substantial biomass needed for such organism to survive. And the reason whales grow to such sizes, asides from the buoyancy of the water, is the amount of plankton available.

So my question is:

Whether or not "Sand Plankton" is possible or not?

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    $\begingroup$ It had better be possible! The spice must flow. $\endgroup$
    – Qami
    May 10, 2021 at 19:51
  • $\begingroup$ Agreed. Other wise how am I suppose to pass my math exam? $\endgroup$
    – Seraphim
    May 10, 2021 at 19:57
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    $\begingroup$ Just hire a mentat instead. $\endgroup$
    – DKNguyen
    May 11, 2021 at 20:30
  • $\begingroup$ photosynthetic desert organisms that live is sand already exist look at cryptobiotic crust. the the productivity is abysmal because of the lack of water, you are not supporting megafauna off of it. $\endgroup$
    – John
    May 11, 2021 at 20:36
  • $\begingroup$ But DKNgyen What would a mentat use but spice? Not to mention how the highliners would be piloted. And don't get me started on amat.... $\endgroup$ May 12, 2021 at 1:09

4 Answers 4

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Deserts are seldomly devoid of life - many deserts are inhabited by beings such as ants, badgers, kangaroo rats, lizards, snakes and camels. Each of these beings carries a microflora and a microfauna inside. As those animals defecate in the desert, their droppings spread microbes around.

Many microbes die from the excessive heat by day or excessive cold by night. The nutrient value of those microbes is not completely lost, though. Also many form spores which await for the next animal to come by ik order to fetch a ride in a new host.

And it's these microbes and their remains that the filter feeding sand swimmers consume.

Which is also why those creatures stalk human travellers. They are not after you, they are after your [redacted].

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MAYBE!

Sticking strictly with terrestrial biochemistry, no. Given the extreme diversity of life and the extent to which is has colonized every conceivable Earthly environment, and some that were not conceivable until we were surprised to find life there after all, I think it's safe to say that if sand plankton were possible to evolve starting from the kinds of organisms that exist on Earth, they would have. Since they haven't, that's a strong indicator that they can't.

But there are theoretical alternative biochemistries that might make it plausible.

There are two big challenges to overcome for sand plankton:

  1. Solvent availability.
  2. Energy supply.

Deserts are deserts precisely because they don't get a lot of water input. That constrains how much total biomass they can contain, because all life on Earth requires water. But suppose that weren't a constraint? If your organisms could manufacture their own biosolvent out of more readily available materials, the lack of rain or rivers would no longer constrain plant growth. If you don't want to stray too far from water-based biology, this could be the case for creatures whose biosolvent is not pure water, but a strongly hygroscopic water solution; e.g. a high-percentage hydrogen peroxide solution, which will pull water out of the atmosphere at extremely low vapor pressures, with the recovered water being cracked to produce more hydrogen peroxide, which will then suck more water out of the air, and so on. Or, if the right kinds of minerals are present, they could use a deliquescent salt solution (e.g., water and potassium carbonate). A third option might be formamide as a sole biosolvent, not mixed with water--water is require to produce it, but like hydrogen peroxide it is strongly hygroscopic, so that lack of liquid water in the environment isn't an issue--plants could simply extract water, nitrogen, and CO2 from the air and make their own liquid formamide.

However you want to solve that problem, once it is solved, you can now have deserts with nearly as much biological productivity as any other environment--perhaps a little less since more primary energy input would go towards making biolsolvent that might be provided for free elsewhere, which is energy that could not then go into other biological activities, but still, you could have a desert surface entirely covered with photosynthesizers, capturing plenty of chemical energy to power a complex ecosystem complete with megafauna.

But that gets us stuck on the second issue: you can cover the surface. Sand may be easier to burrow through than clay or soil, but even sand made of pure transparent quartz scatters and diffuses light extremely quickly, such that it is essentially as dark as the bottom of the ocean only a few centimeters, at most, from the surface. Which means that unlike the ocean, you will not get primary production occurring in a deep column below the surface, and there will not be significant amounts of plankton to bother sifting out below the surface. Just like anywhere else on land, it make more sense to just graze at the surface. However, there may be another way to get around this.

Due to the lack of thermal inertia provided by liquid water, sand dunes (and deserts in general) tend to undergo significant thermal cycling between day and night. At sufficient depths, these cycles average out, and you end up with a fairly constant day-round and year-round temperature--but that doesn't occur until you get around 15 feet down. Above that level, sand is reliably heated by the sun every day, and cooled at night, with the gradient becoming larger the closer you are to the surface. There are a number of electrophysical and chemical systems whose equilibrium points are strongly temperature dependent, so one could imagine alien microbes which extract energy directly from thermal cycling, rather requiring direct exposure to light--as they warm up during the day, the equilibrium point of some chemical reaction shifts, and they extract energy from gating the motion of the reactants in that direction, much like we gain energy in ATP synthase from gating the motion of hydrogen ions. And as they cool down again at night, the equilibrium shifts in the other direction, and they can extract energy again moving molecules the other way. This would give you an excuse for some level of primary production plausibly up to 5 or 10 feet under the surface. That then provides an incentive for burrowing creatures to evolve to eat those microbes, which will result in disturbing and rotating the sand, producing vertical migration of plankton which will further enrich the quantity of food available below the surface.

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Sand plankton may be possible as a niche organism (after all, ice-worms are a thing) but they are going to be very limited in number simply because light does not penetrate sand to any great depth. So while they may exist I argue they do not exist in great enough numbers to support mega-fauna. (Even filtering sand to extract plankton may well be an energy-losing effort).

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The Sand of your deserts is actually the dried silica shells of the "Sand Plankton" A long time ago a new organism evolved a silica shell for protection. It is an extremophile for both hot, cold, and dry conditions. Sand Plankton grow in patches in the desert, usually near Oasis, and also grow at the edges of the desert.

On Earth, cellulose based organisms existed for hundeds of thousands of years before an organism evolved that could break down cellulose. Your planet is the same but with a silica shell (Or anything else you want) There are no bacteria which can break through the hard shell. However, there are the megaworms which grab great mouthfuls and grind it with their stone-like teeth. The precious nutrients are released and available for digestion.

The worms are most certainly eating more Plankton a day than are being produced, but fortunately theres whole deserts 300m deep of the stuff. Now, the worms are highly territorial due to their evolution and regularly kill each other. This keeps their population numbers down and prevents overpopulation from consuming all the food.

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