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The planet in question is Earth-like in size and composition and orbits a Sun-like star. Its atmosphere is less than 5% Oxygen and plants (lichens, some grass and river vegetation) have started colonizing parts of its surface.

How would bodies decompose in this environment?

The bodies are either human or animal and at the time of death contain as much bacteria and wear roughly the same kind of clothes as they would have on Earth.

I'm curious to know if they would rot, dry or stay somewhat "preserved", during a time period of at least one month.

A few types of terrains interest me particularly:

  • Rocky plains with no vegetation, strong winds, plenty of sunlight and regular rains (1-3 times a week).

  • Bottom of a canyon, next to a river, protected from winds and receiving barely any sunlight.

  • Dry cave, no rain, wind, or sunlight.


EDIT :

There is no fauna on the surface - only in oceans and rivers.

The time period should be at least one month and can be as long as needed for the process (rotting, drying, or other) to be well-advanced. I'm not particularly interested on what would happen to the bodies after centuries or millennia.

The mentioned terrains are in a temperate climate, with temperatures varying between 15°C and 35°C.

If someone can give a general answer including other climates and types of terrains, it would be appreciated.


Other questions related to the same setting (if you want more details, but they shouldn't be needed to understand/answer this one):

Space wizards city: Is it sustainable?

How should the Magic market be regulated?

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    $\begingroup$ Your question is unanswerable because decomposition depends on so many more factors than the ones you mentioned. Humidity, temperature, flora in presence of the body, etc. I can say one thing though: one month is nowhere near enough to get the process to a somewhat "final" state. Egyptian mummies took 70 days(!) to dry out and then the desiccation process had lots of help from the embalmers by placing it in natron. en.wikipedia.org/wiki/Mummy#.22Most_perfect.22_method $\endgroup$ – MichaelK Jun 18 '16 at 11:28
  • $\begingroup$ @MichaelKarnerfors Ok, I'll add more information. About fauna, what should I add to "same bacteria inside the bodies as on Earth" and the details of grass/lychen/algae? $\endgroup$ – Babika Babaka Jun 18 '16 at 11:45
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    $\begingroup$ Isn't it more a case of "What conditions are needed to get the outcome I want for the story"? :) Please describe what you want here: to know what realistically would happen, given that some conditions of this planet are very fixed? Or to know what conditions are needed to get the bodies into a certain state? If neither the conditions of the planet are fixed, not the state of the body you wish for people to find it in... then you are free to make up whatever you want. $\endgroup$ – MichaelK Jun 18 '16 at 11:48
  • $\begingroup$ @MichaelKarnerfors During the story, a bunch of dead bodies (human and animal) are found in the "lifeless" parts of the planet. I'm mostly interested in making it realistic, that's why I'd like to know if bodies would still rot if left on the surface of a planet with no fauna and low oxygen levels. $\endgroup$ – Babika Babaka Jun 18 '16 at 12:22
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    $\begingroup$ @MichaelKjörling It is... which is why I asked the questioner: what is it that you need for your story? Answering questions is not only about thinking about the relevant factors for the question but the relevant factors for the questioner as well. The questioner is asking in order to find a solution to something. That something can affect the answer in a big way. :) $\endgroup$ – MichaelK Jun 18 '16 at 12:55
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tl;dr: The corpses would still decay, but probably much slower.

From the Wikipedia article about decomposition:

Decomposition begins at the moment of death, caused by two factors: autolysis, the breaking down of tissues by the body's own internal chemicals and enzymes, and putrefaction, the breakdown of tissues by bacteria. These processes release gases, such as cadaverine and putrescine, that are the chief source of the unmistakably putrid odor of decaying animal tissue.

Prime decomposers are bacteria or fungi, though larger scavengers also play an important role in decomposition if the body is accessible to insects, mites and other animals.

Clearly autolysis would happen also on that planet. So the question is which, if any, of the necessary bacteria and fungi are likely available (from your assumptions, animals aren't).

Wikipedia goes more on detail on the different stages:

Five general stages are used to describe the process of decomposition in vertebrate animals: fresh, bloat, active and advanced decay, and dry/remains.

For the fresh stage, especially the following paragraph is interesting for your question:

The small amount of oxygen remaining in the body is quickly depleted by cellular metabolism and aerobic microbes naturally present in respiratory and gastrointestinal tracts, creating an ideal environment for the proliferation of anaerobic organisms. These multiply, consuming the body's carbohydrates, lipids, and proteins, to produce a variety of substances including propionic acid, lactic acid, methane, hydrogen sulfide and ammonia. The process of microbial proliferation within a body is referred to as putrefaction and leads to the second stage of decomposition, known as bloat.

With your low-oxygen environment (which probably was once a no-oxygen environment) I'd expect especially the anaerobic bacteria to thrive, therefore I'd expect the body to at least go to the phase of bloat.

The description of the bloat phase in the Wikipedia article should be relevant except for the last paragraph, which refers to insects/maggots.

The active decay phase is described as follows:

Active decay is characterized by the per of greatest mass loss. This loss occurs as a result of both the voracious feeding of maggots and the purging of decomposition fluids into the surrounding environment.[11] The purged fluids accumulate around the body and create a cadaver decomposition island (CDI). Liquefaction of tissues and disintegration become apparent during this time and strong odors persist.[6] The end of active decay is signaled by the migration of maggots away from the body to pupate.

Now the maggots would not be there in your environment, therefore I'd expect the active decay phase to be much less active. However note that the purging of decomposition fluids should happen also in your environment.

So in summary, I'd say you'd certainly go into the bloat phase, and you'd probably get a decomposition phase, but not as fast as on earth.

For your cave scenario, also the following paragraph seems relevant:

A body buried in a sufficiently dry environment may be well preserved for decades. This was observed in the case for murdered civil rights activist Medgar Evers, who was found to be almost perfectly preserved over 30 years after his death, permitting an accurate autopsy when the case of his murder was re-opened in the 1990s.

I guess the burying part is only for preventing access by animals, which means the same should be true for the dry cave scenario.

This page also contains relevant information:

It is also important to note that the internal organs of the deceased will begin to decay in a particular order; beginning with the intestines, which as well as holding bacteria also hold various levels of acidic fluid which – when unable to circulate – begin to eat through their surrounding tissues. As the intestinal organs decay so too do the liver, kidneys, lungs and brain. The contents of the stomach may also slow down the rate of decay if there is undigested food in and around that area.

Clearly those intestine bacteria would be present also in humans on your planet, as without them the humans couldn't live to begin with.

Also on this page there's a hint that lack of oxygen slows down decomposition:

If a body is left submerged in water the rate of decomposition will typically be much slower due to the low temperatures and levels of oxygen, unless the corpse is able to float to the surface where insect colonization can occur.

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Giving a general answer is difficult, so you are actually free to make up a lot of this stuff yourself.

The Wikipedia page on Decomposition provides lots of information. What makes your planet a special case if that fauna, insects and animals are absent. This means that the decomposition will be driven mostly by oxidation and chemical processes, and whatever microbes is present in the corpses when they die.

In your case you need to leave out all factors that animals, insects and plant do for a corpse on Earth. Depending on how much rain the corpses are subjected to, this will affect things.

But I would say that the unfortunate souls that find the dead ones will be treated to a fairly icky sight. Anaerobic decomposition (i.e. without much oxygen present) will probably dominate the decay. This means that they will be gassy, bloated, and stink badly.

If they are in environmental suits it will not seem bad at first... other than a very rotting look on their faces. But any attempt at autopsy will likely result in a stomach-churning experience.

In fact... Mythbusters' experiment of leaving a corpse (of a pig) in a car is probably a very good analogy.

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