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An alien species I have been working out recently lives on a high gravity planet. Because of this, they need to be able to gain muscles fast. Of course this is given since birth, but they need other supplements. So I figured that because some rocks have certain minerals in them that help with muscle growth, that they'd be able to eat and digest them

The path of evolution for this would be that they started off drinking mineral rich water on the planet, and as time went on, their stomachs would be better at digesting and using the minerals. So over time, their teeth strengthen somehow (I am working that out) and they are successfully able to chow down on some rocks.

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  • $\begingroup$ You might be interested in the questions Can anything survive by eating rocks and other ground minerals? and especially Could eating rocks provide sufficient calories for survival? $\endgroup$
    – Secespitus
    Apr 20, 2018 at 11:46
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    $\begingroup$ I'd suggest avoiding chewing the rock. there are various animals that eat rocks or similar without chewing $\endgroup$
    – user45032
    Apr 20, 2018 at 11:47
  • $\begingroup$ I don't get the actual question. There are no rules, you can make up whatever you want. You even offer an explanation. What else do you want to know? Specifics about the stomach of those creatures? If this makes sense or if there is a better way? What kind of rocks? You state you are working out the teeth yourself, so I guess it's not about those at least. Please note that humans and so on are able to use tools for millions of years now, you don't need to chew them with special teeth - given what you wrote about how you picture the evolution part, this might be a bit of a hole $\endgroup$
    – Raditz_35
    Apr 20, 2018 at 11:50
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    $\begingroup$ There is one type of rock which humans eat. It's called halite. It contains "certain minerals" which are essential for human life. $\endgroup$
    – AlexP
    Apr 20, 2018 at 11:51
  • $\begingroup$ The term you want to help your research is "lithovore." $\endgroup$
    – SRM
    Apr 20, 2018 at 15:11

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As the other answers have pointed out, rocks as we know them would not be something that anything remotely resembling humans would be able to eat...

Which is why I propose a different solution. This high-gravity planet has a lot of extra force. Perhaps the "rocks" aren't quite the same as they are on earth.

All it would require is organic matter in the rocks, and then there might be some nutritional value in eating those rocks, assuming that their digestive systems are adapted to provide some method of both processing the rocks and extracting the organic material from them.

It's easy enough to come up with hypothetical reasons why organic material is found within the rocks. The easiest one for me to come up with is that evolution led to large amounts of Lithotrophs throughout the planet's surface areas. These Lithotrophs essentially convert some of the rock into organic substances, which can then be used by the alien's body more easily. This would be more easily accomplished if certain elements are particularly common in the soil, etc.

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    $\begingroup$ not to be picky, but answering to "can an organism grow eating rocks?" with a "yes, eating organism growing or rocks" is a bit like telling that eating a steak is like eating salad, since cows eat salad. $\endgroup$
    – L.Dutch ♦
    Apr 20, 2018 at 14:05
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    $\begingroup$ @L.Dutch I'm vegetarian per proxy. Cow eats plants, I eat cow ;) $\endgroup$
    – Mołot
    Apr 20, 2018 at 14:49
  • $\begingroup$ @L.Dutch - my answer isn't "organism growing on rocks", but "organic material in the rock". Note the difference between "organic" and "organism" - "organic" is a chemistry term, and refers to the kinds of chemicals, usually the kinds of chemicals that are the basis for life (meaning it's typically also what is left behind by life). $\endgroup$
    – Glen O
    Apr 20, 2018 at 16:15
  • $\begingroup$ Lithotrophs grow on rocks, feeding on rocks. Is this not what you stated? $\endgroup$
    – L.Dutch ♦
    Apr 20, 2018 at 16:20
  • $\begingroup$ @L.Dutch I gave Lithotrophs as an example, suggesting that they're a lot more common on the alien planet as one plausible explanation for how more organic matter could be found in rocks. I did not suggest that they were simply on the surface and were the only reason for the organic matter. $\endgroup$
    – Glen O
    Apr 20, 2018 at 16:32
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No, not really

Muscles, as we know them, are mostly protein*. Rocks are mostly inorganic matter. Anything that evolves similarly to humans can't process inorganic substances into organic ones on the mass scale. It requires a lot of energy to do so, that's why we "outsource" this to plants, and plants use energy from the sun.

Small amounts of minerals are, indeed, needed, but the way our bodies work, providing too much would not be helpful and may outright kill. No biology even remotely similar to ours could deal with that, sorry.

Now, with truly alien biology this isn't as impossible. Only "race that evolved similarly to humans" is a problem.

* Well, everything in human is mostly water, so I was talking about dry mass. As Raditz_35 says, if you count water, and if ice can technically be classified as mineral... But I don't think that's what you wanted.

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  • $\begingroup$ Muscles are mostly water. So if they chew ice cubes, which might be considered a mineral ... $\endgroup$
    – Raditz_35
    Apr 20, 2018 at 11:58
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    $\begingroup$ @Raditz_35 in biochemistry water is "omitted by default" unless important in given context, as far as I know. But sure, I'll clarify. $\endgroup$
    – Mołot
    Apr 20, 2018 at 12:00
  • $\begingroup$ Okay, so what I mean when I say they evolved similarly is that my artistic ability is very limited and so the only concept art I have of them is basically just humans, except they are tall, and the females have 4 arms. Internally, they are pretty different. I guess this is stuff I should have added to the body of my question, apologies. $\endgroup$
    – Alyssa S.
    Apr 20, 2018 at 12:03
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    $\begingroup$ @AlyssaS. When you give up on human biology, pretty much anything goes, just make sure it makes sense energy-wise. $\endgroup$
    – Mołot
    Apr 20, 2018 at 12:18
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Minerals alone are not enough to make a body grow fast. Sure, they are important, but no body is made of just minerals.

Also consider that their metabolic supply is pretty low: if they are available as rocks it means they are already in (or closest to) the lowest free energy level for that planet. So there is really not much to gain by playing chemistry with them.

In fact plants use minerals to build up organic matter, not to get energy.

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    $\begingroup$ +1, good point about energy $\endgroup$
    – Mołot
    Apr 20, 2018 at 12:22
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You can't really "digest" minerals. Acids don't really do a lot to them, so the only way to really get at them it to either crush them into tiny bits or dissolve them in water if they're salts.

http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/absorb_minerals.html

As displayed in the source above, the body just absorbs tiny bits of minerals in the colon.

As others have pointed out, it would also take a LOT of energy to crush and absorb the minerals. You could approach this by saying that the rocks on the alien planet are impure and are basically made of carbon (or sugar) AND the mineral, which would make digesting easier and they'd actually be able to get energy from it.

You could also take a whole different approach and say that they need salts to create some sort of bio-battery in their muscles. But I'm not sure how viable that is.

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I think there is another issue, apart from nutrition, that makes this scenario implausible. Rocks are too plentiful, so a creature eating them would essentially be grazing. I suspect this alien race would become a kind of alien cow.

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