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One of my fictional planets is a lot like Venus. Tons of volcanoes, extreme air pressure, similar density. The volcanoes are active. There is 1 creature here that depends on minerals and acids. Without acids, these creatures would be toast.

Okay here is what I am proposing for a creature who absolutely need minerals and acids:

The creatures have a cold field around them to protect them from volcanic temperatures. They are very heat resistant on the inside and as soon as lava gets into the mouth, it is supercooled. This supercooled lava is then digested by an extremely strong acid.

Then the minerals are surrounded by weak polyprotic acids. This protects them from the HCl that is in their blood.

HCl is like water for these creatures in that it is absolutely crucial to living. If HCl levels get low on the planet, a lot of these creatures will die from lack of acid.

Is it plausible that these strong acids are like water in that they are necessary for these creatures to live?

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  • $\begingroup$ Protein-based stuff is rather tolerant to acids. What you propose is of course impossible, but not as bad as e.g. blood that contains a large amount of sodium hydroxide. Because that would just turn liquify you, completely. $\endgroup$ – Karl Mar 25 '17 at 22:07
  • $\begingroup$ The human stomach produces hydrochloric acid, so you might want to read up on that. en.wikipedia.org/wiki/Gastric_acid $\endgroup$ – DrBob Mar 26 '17 at 16:19
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First, Venus has not too much HCl, it has a much more sulfuric acid H₂SO₄. But from the viewpoint of the answer, it is the same.

These acids have 2 major effects for us:

  1. they change the biochemical reactions of our proteins. Many biochemical processes work differently in acidic environment. Essencially, they are poisons. For us.
  2. they chemically destruct the proteins.

Thus, they are destructive and also poisonous.

None of them is unavoidable, it is only because the ancient oceans in them our biosphere started, simply wasn't any of them.

But note: the main structure of the proteins are chemically strong things, around like the plastic materials. It is not an inherent disadvantage, a life could evolve in a such acidic environment without any major problem.

Although their biochemical reactions would then require the acidic environment, thus the life in our clean water would be similarly unavoidable for them, as living in NaOH for us.

You don't need some internal protection for them from their acidic blood, their whole body can be simply acidic. With sulfuric acid, and not with HCl.

What is a major problem: They still need water. Without water, there are no complex biochemical reactions. Or, you need some fluid. And the Venus is so dry like the Sahara.

Furthermore, Venus is too hot, with 400°C surface temperature makes the long molecular chains simply impossible.


Note: HCl is a gas, it will be fluid only far below 0° C. What we call hydrochloric acid, is its solution in water.

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One thing about World Building is that it works according to your whims and fantasies. Maybe on another planet, a silicon-based intelligent alien kid would be asking her grandfather "Pa, is it possible that on a planet far far away, there could be life forms based on carbon compounds instead of silicon?"

The point is that you go on and make your creatures the way you want them. You cannot make your creatures 100% practical and flawless. No, even if a team of 100 top scientists sits together and works on such an alien creature for a year, they would definitely come up with a generally working model, but the minute details would still have to be filled in and a lot of little errors and loopholes here and there to be fixed.

So go on and design your creatures the way you want them. In my this answer I could go the negative way and try to find critical flaws in your creature design, but who am I (or anyone else) to criticize? It is your world, you make it as you like it.

Now, coming to life as we know it, I don't think it would be easy to define a creature so different from Earthly life. There are a lot of things which need to be in place, in order to make it work even in the most rudimentary form. For one, a creature depending so heavily on HCl that it would die in its absence sounds like it has evolved in a predominantly alkaline environment. Venus (or any super-volcanic planet) is far, faar from being alkaline at all.

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