Let's create an alien biosphere!

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Do you mean the photosynthetic reactions?

Yes.

[Schiaparelliorbust]

Yes.

I had assumed that they were going to all create oxygen, but are there alternatives? I just looked it up and couldn't find any.
Edit: I found this: https://en.wikipedia.org/wiki/Anoxygenic_photosynthesis

[MathAndCode]

I had assumed that they were going to all create oxygen, but are there alternatives? I just looked it up and couldn't find any.
Edit: I found this: https://en.wikipedia.org/wiki/Anoxygenic_photosynthesis

The idea is that they will need to create the reactants in their energy-creating reactions that they cannot readily get from the environment. However, we should consider that the predators will evolve to digest biomolecules for energy, so a predator that evolves photosynthesis may synthesize one or more biomolecules directly instead of making simpler molecules first.

[Schiaparelliorbust]

The idea is that they will need to create the reactants in their energy-creating reactions that they cannot readily get from the environment.

There isn't any oxygen yet. Would they create that?

However, we should consider that the predators will evolve to digest biomolecules for energy, so a predator that evolves photosynthesis may synthesize one or more biomolecules directly instead of making simpler molecules first.

I don't get why the first part causes the second part.

[MathAndCode]

There isn't any oxygen yet. Would they create that?

That depends on what the necessary reaction is.

I don't get why the first part causes the second part.

The organism would want to create substances that it already knows how to use as fuel.

[Schiaparelliorbust]

That depends on what the necessary reaction is.

Is the the respiration (energy creating) reaction we're talking about?

The organism would want to create substances that it already knows how to use as fuel.

So you're saying it would try to create something that it could use for energy directly. Why should this matter?

[MathAndCode]

Is the the respiration (energy creating) reaction we're talking about?

Yes.

So you're saying it would try to create something that it could use for energy directly. Why should this matter?

It would need to be able to use the fuel that it generates. Otherwise, making that fuel would be useless.
Photosynthesis in plants on Earth creates glucose. Glucose wouldn't have been floating around the prebiotic oceans for life to use as fuel once it evolved, but it's used in the cell wall of plants, algae, and other organisms, and some bacteria use it to create biofilms.

[Schiaparelliorbust]

Is the the respiration (energy creating) reaction we're talking about?

Yes.

Ok good. I was confused. I never thought about cyanobacteria actually using the oxygen they created. I thought it was just a useless byproduct at first.

It would need to be able to use the fuel that it generates. Otherwise, making that fuel would be useless.
Photosynthesis in plants on Earth creates glucose. Glucose wouldn't have been floating around the prebiotic oceans for life to use as fuel once it evolved, but it's used in the cell wall of plants, algae, and other organisms, and some bacteria use it to create biofilms.

Let's keep the fuel simple then. There's stuff like acetylene (C2H2) that is simple, but it is highly flammable, so we might not want that in our atmosphere.

[MathAndCode]

Ok good. I was confused. I never thought about cyanobacteria actually using the oxygen they created. I thought it was just a useless byproduct at first.

It was. The substances they had to start with were carbon dioxide and water, and they wanted to generate hydrocarbons (possibly with some oxygen atoms—but definitely with not so high of a proportion of oxygen atoms), so they had to get rid of oxygen. Their starting materials and their end goal determined the reaction, including what the waste products would be.
Also, for the composition of the oceans, I just remembered that there will be some ammonia, hydrogen cyanide, isocyanic acid, and formamide in the water, so there will probably be some early reactions involving nitrogen.

[Schiaparelliorbust]

It was. The substances they had to start with were carbon dioxide and water, and they wanted to generate hydrocarbons (possibly with some oxygen atoms—but definitely with not so high of a proportion of oxygen atoms), so they had to get rid of oxygen. Their starting materials and their end goal determined the reaction, including what the waste products would be.
Also, for the composition of the oceans, I just remembered that there will be some ammonia, hydrogen cyanide, isocyanic acid, and formamide in the water, so there will probably be some early reactions involving nitrogen.

I can't find anything on combustible or flammable alkaloids (nitrogen containing compounds). Do you have any idea how they might use nitrogen?

[MathAndCode]

I can't find anything on combustible or flammable alkaloids (nitrogen containing compounds). Do you have any idea how they might use nitrogen?

While nitrogen can form thermodynamically stable compounds, it tends to not want to bond to other elements as much as other nonmetals, such as oxygen, so there's a good chance that photosynthesizers would turn it into dinitrogen gas.

[Schiaparelliorbust]

While nitrogen can form thermodynamically stable compounds, it tends to not want to bond to other elements as much as other nonmetals, such as oxygen, so there's a good chance that photosynthesizers would turn it into dinitrogen gas.

I was thinking of nitrogen in the fuel compound. I guess that wouldn't work.

[MathAndCode]

I was thinking of nitrogen in the fuel compound. I guess that wouldn't work.

It could work. Ammonium nitrate, nitroglycerine, and trinitrotoluene are explosives, demonstrating that nitrogen-containing compounds can store chemical energy that can be released.

[Schiaparelliorbust]

It could work. Ammonium nitrate, nitroglycerine, and trinitrotoluene are explosives, demonstrating that nitrogen-containing compounds can store chemical energy that can be released.

How did I not think of nitro compounds? But if we do use them we should make sure that they aren't produced in high quantities/used before they escape the microorganism or they might explode. And I doubt that there would be much evolutionary pressure at first to do this unless the heat from hydrothermal vents could detonate them.

[MathAndCode]

How did I not think of nitro compounds? But if we do use them we should make sure that they aren't produced in high quantities/used before they escape the microorganism or they might explode. And I doubt that there would be much evolutionary pressure at first to do this unless the heat from hydrothermal vents could detonate them.

Not all potential nitrogen-containing reactants must be high explosives that the organisms must be careful to store safely. For example, CH₃NO+HNCO→N₂+CO₂+CH₄ is exothermic, and formamide and isocyanic acid will be dissolved in the oceans.

[Schiaparelliorbust]

Not all potential nitrogen-containing reactants must be high explosives that the organisms must be careful to store safely. For example, CH₃NO+HNCO→N₂+CO₂+CH₄ is exothermic, and formamide and isocyanic acid will be dissolved in the oceans.

Ok good. Neither of them are flammable. One thing though is that once there is oxygen in the atmosphere, there won't be nearly enough carbon monoxide to form formamide (CO + NH3 → HCONH2).
Edit: It actually forms from the hydrolysis of hydrogen cyanide, which we already have a lot of.

[MathAndCode]

Ok good. Neither of them are flammable. One thing though is that once there is oxygen in the atmosphere, there won't be nearly enough carbon monoxide to form formamide (CO + NH3 → HCONH2).

Yes, but at that point, organisms will have come to rely on it, so they will manufacture it, and some of it will escape the organisms and go into the ocean.

[Schiaparelliorbust]

Yes, but at that point, organisms will have come to rely on it, so they will manufacture it, and some of it will escape the organisms and go into the ocean.

I made an edit. There's also a whole Wikipedia page on formamide-based prebiotic chemistry.

[MathAndCode]

I made an edit. There's also a whole Wikipedia page on formamide-based prebiotic chemistry.

That Wikipedia article reminded me that hydrogen cyanide could also serve as a source of energy. 2HCN→N₂+C₂H₂ is exothermic, but there's probably something better.

[Schiaparelliorbust]

That Wikipedia article reminded me that hydrogen cyanide could also serve as a source of energy. 2HCN→N₂+C₂H₂ is exothermic, but there's probably something better.

We probably don't want that anyway because acetylene (C₂H₂) is explosive. I also found a NASA article on formamide too: https://astrobiology.nasa.gov/news/why- ... -to-water/.

[MathAndCode]

We probably don't want that anyway because acetylene (C₂H₂) is explosive. I also found a NASA article on formamide too: https://astrobiology.nasa.gov/news/why- ... -to-water/.

I doubt that acetylene would explosive in the absence of oxygen (or another oxidant). However, I found another reaction that is about six times as exothermic per mole of hydrogen cyanide. HCN+NH₃→N₂+CH₄

[Schiaparelliorbust]

I doubt that acetylene would explosive in the absence of oxygen (or another oxidant). However, I found another reaction that is about six times as exothermic per mole of hydrogen cyanide. HCN+NH₃→N₂+CH₄

May I ask how you find how much energy these reactions produce?

[MathAndCode]

May I ask how you find how much energy these reactions produce?

Subtract the sum of the enthalpies of formation of the products (multiplying each by the molar coefficient for that product) from the sum of the enthalpies of formation of the reactants (multiplying each by the molar coefficient for that reactants) in order to get the amount of energy released by the reaction.

[Schiaparelliorbust]

Subtract the sum of the enthalpies of formation of the products (multiplying each by the molar coefficient for that product) from the sum of the enthalpies of formation of the reactants (multiplying each by the molar coefficient for that reactants) in order to get the amount of energy released by the reaction.

Thanks! So the microorganisms use HCN+NH₃→N₂+CH₄ and heat from the hydrothermal vents to get energy. Should they photosynthesize formamide?

[MathAndCode]

Thanks! So the microorganisms use HCN+NH₃→N₂+CH₄ and heat from the hydrothermal vents to get energy. Should they photosynthesize formamide?

Theoretically, yes, but they'll have no reason to unless they use it to get energy.