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I'm just starting with the original novel but have an interest in desert planets so bear with me please.

Per Wikipedia:

It seems the sandworms are responsible for Arrakis becoming a desert planet:

The sandtrout [...] was introduced here from some other place. This was a wet planet then. They proliferated beyond the capability of existing ecosystems to deal with them. Sandtrout encysted the available free water, made this a desert planet [...] and they did it to survive. In a planet sufficiently dry, they could move to their sandworm phase.

OK so the sandworms are responsible for the water being under ground.

And then another explanation:

The non-canon Dune Encyclopedia (1984) theorizes that the depletion of the oceans (the primary result of which was desertification) was probably caused by the impact or near miss of a comet or other quasi-planetary body. This event caused the loss of much of the atmosphere of Arrakis, allowing most of the oxygen and water to escape into space. This is thought to have occurred approximately 50 million years before the Imperium's creation. This catastrophic loss of oxygen led to the extinction of nearly all native fauna and then therefore the flora.

OK I get that. But now the sandworms are back:

The Encyclopedia also explains that one of the few forms to survive were tiny worms of the phylum Protochordata. One of these forms was Shaihuludata, a genus of anaerobic burrowing worm that was the basal species from which the giant sandworms (Geonemotodium arraknis or Shaihuludata gigantica) evolved. Rather than sandworm creating desert, it was desert that created sandworm. The mass extinction of all of its predators and competitors for food allowed the animal, in a manner somewhat analogous to the evolution of unique faunal forms on isolated Terran islands, to take the evolutionary path that would not only re-oxygenate the Arrakeen atmosphere, but also create the spice melange with all of its immense consequences for humanity.

OK now instead of killing all life on the planet they re-oxygenated the atmosphere and (seemingly) brought biological life forms back at the same time. Again, how would they have made that happen without water?

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    By my understanding, it was always the sandtrout that resulted in the desertification. The water of Arrakis never went away, it just all got clustered underground in sandtrout cysts (and converted to pre-spice mass), and the sandtrout were not native to Arrakis as the Encyclopedia states. You may want to explore the other questions on this site regarding Dune and sandworms/sandtrout (but beware spoilers!).
    – JAB
    Commented Sep 5, 2017 at 19:30
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    Oxygen is still there. People can breathe on Arrakis just fine with no masks or anything. It's just very dry and possibly hot.
    – void_ptr
    Commented Sep 5, 2017 at 20:05
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    a non-canon resource probably not the most authoritative place to start asking questions from - in other words, since even the first book establishes that Arrakis isn't lacking water, this is a dubious claim the encyclopedia is making
    – NKCampbell
    Commented Sep 5, 2017 at 21:05
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    "God created Arrakis to train the faithful." - The Wisdom of Maud'Dib
    – user15742
    Commented Sep 6, 2017 at 1:03
  • In fact, the worms create oxygen. Leto II describes their body as an enormous factory that exhales oxygen as a by-product. When they move along the sand at full speed, there is a trail of fire behind them as the oxygen gets ignited by friction.
    – Omegacron
    Commented Nov 30, 2017 at 21:20

2 Answers 2

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Sandtrout encysted the available free water, made this a desert planet [...] and they did it to survive. In a planet sufficiently dry, they could move to their sandworm phase.

But how would the sandworms have accomplished that?

Something, something, something evolution. :) Considering that you and I and all mammals including the 100 ton Blue Whale descended from this cute guy 250 million years ago...

enter image description here

We got Blue Whales from that? Giant sand worms from trout? Sure.

As for changing the makeup of an entire planet, here on Earth these tiny cyanobacteria (ie. blue-green algae) were responsible for oxygenating our planet.

enter image description here

So sure, a single species could be responsible for locking all the free water up underground.

Shaihuludata, a genus of anaerobic burrowing worm that was the basal species from which the giant sandworms...

An anaerobic organism is one that does not require oxygen for growth.

in a manner somewhat analogous to the evolution of unique faunal forms on isolated Terran islands, to take the evolutionary path that would not only re-oxygenate the Arrakeen atmosphere, but also create the spice melange with all of its immense consequences for humanity.

Presumably, Shaihuludata gigantica expels oxygen and melange as part of its respiratory process.

Typical aerobic respiration, what you and I do, takes in oxygen and glucose and reacts them to create carbon dioxide and water and heat. The carbon dioxide and water get expelled, and we use the resulting heat for energy.

C6 H12 O6 + 6 O2 → 6 CO2 + 6 H2O + heat

Shaihuludata gigantica takes in... something and expels oxygen and melange. I don't know of any Earthly non-photosynthesizing anaerobic process that expels oxygen, but hey, it's an alien. Some will expel water, which might then be split by some geological or biological process to hydrogen and oxygen.

The problem is the time scale, 50 million years is a bit quick. Our oxygenation took about 2.5 billion years. OTOH a lot of that was spent saturating the oceans and land surface with oxygen. If Arrakis was once oxygenated, these oxygen sinks might already be full and the process would "only" have to fill the atmosphere.

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  • Two questions. If the water is underground now, it's still salty and unfit for human consumption prior to removing the salt? When you say that the land mass was once oxygenated (the oceans are of course gone), you mean that sand and rocks are satiated with oxygen even when it's gone from the atmosphere?
    – H3R3T1K
    Commented Sep 5, 2017 at 20:17
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    @H3R3T1K There's no reason underground water has to be salty, nor does it have to be fit for human consumption to support life (see also: our oceans). Saying more would be spoilers. But water can also be physically trapped in the rock or chemically bonded to the rock like the process of curing that produces concrete. And yes, it could take far more than 50 million years for the oxygen saturated in the geology to out gas naturally.
    – Schwern
    Commented Sep 5, 2017 at 20:23
  • @H3R3T1K You should finish the book, you've already drifted into spoilers knowing that the sand worms produce melange.
    – Schwern
    Commented Sep 5, 2017 at 20:27
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    I don't think sandtrout is actually connected to trout though. It looks like just a popular name given by people clueless about biology, similar to how a “sea cucumber” is nothing like a cucumber, and a “sea cow” is nothing like a cow. This doesn't matter for your answer though.
    – b_jonas
    Commented Sep 5, 2017 at 21:34
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    For the "50 million years is a bit quick", you really do have to take the sinks into account. It has been estimated that with current photosynthesis rate on Earth, it would only take about 6000 years or so to completely replenish all the current oxygen content of the atmosphere. The first time, the final phase once the oxygen sinks (iron ions in oceans, rocks...) were filled took "only" about fifty million years, actually - and that was with primitive cyano-bacteria that still had to compete with anaerobic life, and during a massive glaciation event caused indirectly by all that oxygen.
    – Luaan
    Commented Sep 6, 2017 at 10:37
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Given the non-canonical nature of the Encyclopedia, it is difficult to come up with any explanation beyond what is provided in your quote. The encyclopedia is directly at odds with the published books. That said, I'm willing to provide a (wild) hypothesis.

Things we know, within the non-canonical Encyclopedia's version of events.

  1. Primordial sandworms (aka Shaihuludata) survived the mass-extinction event.
  2. Very little if any other life survived, including all of Shaihuludata's predators and competitors.
  3. During their evolutionary path towards the Sandworm (one particular branch of what would probably be a broad tree), Shaihuludata was somehow involve in or responsible for re-oxygenating the atmosphere.
  4. Protochordata is a very loose category of animals, and is not a proper taxonomic group. There is little we can determine from this classification.
  5. On Earth, the Great Oxydation Event is largely attributed to photo-synthetic Cyanobacteria.

To re-oxygenate the atmosphere, we really need something to photosynthesize. This could be another creature on the planet, which does not compete with the Shaihuludata, though this seems to negate the fact they were involved according to the provided quote.

The worm could have evolved photosynthesis on it's own, but this seems unlikely, as that kind of food/energy change in an existing multi-cellular organism is unheard of.

One option, which seems more likely, is that the Shaihuludata evolved into a symbiotic relationship with some form of bacteria. Similar to how the Giant Tube Worm has evolved symbiosis with chemosynthetic bacteria that also grow around their ocean vents. The symbiosis must be two-way, so that we could in some form state that the Shaihuludata was "responsible" for the re-oxygenation by supporting or even "farming" this unnamed bacteria.

It's possible (even likely) that this theoretical bacteria would be some form of Lithotrope. Using the abundant sunlight and minerals present on Arrakis to provide energy for the Shaihuludata. This interaction could form the basis for a whole colony-ecosystem, leading to the evolution or (more likely) adaptation of other related flora/fauna.

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  • The part about the symbiotic relationship is most interesting. Could you elaborate on what both the worm's and the bacteria's jobs are in this relationship and where the oxygen comes from? What I understood is: Worm eats bacteria and produces oxygen.
    – H3R3T1K
    Commented Sep 5, 2017 at 20:37
  • Theoretically the bacteria could produce energy from minerals (sulfur, or iron are common), sunlight, and carbon dioxide (could be sourced from a volcano) much like purple or green bacteria do on earth. The Worm could have evolved to "farm" these bacteria, by spreading them to regions that could support them, and then eating them for energy. The giant worms can do this internally, since they operate on water. The photosynthetic complement would require our bacteria to be exposed to the sun.
    – ench
    Commented Sep 5, 2017 at 21:02
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    Since these are sandworms we're talking about, they could also spread the bacteria around the top layers of sand. Then pass back through the layers consuming the bacteria with some kind of desert equivalent of baleen. The worms would operate like organic ploughs, constantly bringing new mineral rich sand to the top where the bacteria lives, and in return consuming the bacteria for energy.
    – ench
    Commented Sep 5, 2017 at 21:05
  • I believe that it is stated in canon works (actual canon not Sandercanon) that the sandtrout weren't native to Arrakis to begin with
    – NKCampbell
    Commented Sep 5, 2017 at 21:06
  • Yep, this is discussing the alternative process laid out in the non canon encyclopedia
    – ench
    Commented Sep 5, 2017 at 21:36

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