I myself have always been intrigued about life not based around that mainstream element, Carbon. We all know about silicon, and maybe a few of us ammonia, but are other elements capable of being the base for life? And what kinds of planets could sustain these different organisms? What kinds of ecosystems would develop?
Post by The_Wayward_Admiral on Dec 7, 2015 22:08:01 GMT
Interestingly, there is always methane. I realize that the thread topic is about elemental basis, but you mentioned ammonia, so I'm jumping to solvent. You probably know (or maybe not) that many people are excited about Titan's methane oceans, because a recent computer simulation demonstrated a possible membrane construction based on methane-derived molecules. Methane could act as a neat organic solvent to replace water in cold places, but life wouldn't be able to be sustained from sunlight there, so hydrothermal energy would likely be the most prevalent.
Post by The_Wayward_Admiral on Dec 8, 2015 0:14:17 GMT
Yeah, I've never been a huge fan of silicon for that purpose. It's very heavy, and it only bonds "like" carbon under certain conditions. to say nothing of the fact that it's not as common in planetary discs. It is interesting that it would be slower, is there any more information on that? It's a very intriguing line of thought.
Just so you know, it has been confirmed that Thrive will only have carbon-based life forms. But feel free to continue discussing it.
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Aw, don't be sad, it isn't due to any sort of carbon elitism, the problem is simply that carbon-based, fatty bags of brine full of nucleic acids and proteins is the only form of life we know, and we would not be able to portray any form of life not based on those with any form of realism. Methane-solute life is also out for that reason, we simply don't know enough about how it would work to be able to even propose a system that we could run in Thrive.
Here's a non-exhaustive list of things that we'd have to consider: - Physical properties of primary solvent would dictate the temperature/pressure ranges at which such life could occur - Those would in turn dictate reaction rates, reaction methods, and all the particulars of molecular behaviour - Those in turn would most likely lead to very very different systems for controlling reaction rates. - What kind of energy balances would be involved in the metabolism of this kind of life? - What are the primary reaction intermediates (for example, ATP, Ac-CoA, amino acids) which form the skeleton of the biosynthetic pathways in this kind of life? - How the heck do we even begin extending this stuff into multicellular gameplay?
Fun times. If anyone seriously wants to take a crack at speculating all these answers for something, have at it. You'd earn my deep respect if you manage even a halfway complete job.
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Back on the topic of non-carbon based life, I remember reading somewhere that ammonia based life would require an extremely cold planet in order for anything remotely complex to form. This would mean that any ammonia life would metabolize and evolve at a very slow rate compared to life on Earth. Ammonia is also flammable in oxygen, so would ammonia based life need to evolve on a planet with no oxygen? Instead using a different gas such as nitrogen?
Post by The_Wayward_Admiral on Dec 10, 2015 22:04:10 GMT
Bear in mind that in order to combust, high levels of energy are needed, so Ammonia looses a great deal of flammability at very low temperatures (correct me if I misinterpreted thermodynamics). That being said, Oxygen is very reactive regardless of most situations, so it's kind of nifty that we manage to survive with it (although the same cannot be said for 90% of life a few billion years ago). So Nitrogen would be good, especially since it could be stripped from liquid ammonia like oxygen is from water molecules in our biosphere.
Edit: I should have specified that oxygen/nitrogen is/would be stripped from its liquid for storage molecule synthesis. Inhale as needed for catabolysis.
Dinitrogen is terribly stable, though, so I don't think it could be used in the same way as oxygen is. When oxygen is stripped from water and CO2 to produce energy storage molecules, it's probably better to think of it as oxygen being the energy storage molecule, or rather, that the energy is stored by separating out molecular oxygen, and returned through aerobic respiration.
I know hydrazine is rather unstable, so maybe N-N single bonds (compared to N-H bonds, N-O, N=O, N=N, etc) could be used to carry free energy between reactants. I could see reactions moving electrons between nitrate and amide groups being used a lot, for example.
At such cold temperatures, though, I'm not sure if there would be any way to gain the amount of energy needed to fix nitrogen, so while a lot of reactions could be driven by converting nitrogen species to dinitrogen gas, it would suck if they have to rely on non-biological processes (eg, lightning) to fix nitrogen again. That puts life on a very tight timer, since any life that evolves to make use of the energy provided by producing dinitrogen would simply outcompete and starve anything that gets energy through processes with smaller Gibbs potentials, and then destroy all the available reservoirs of undigested ammonia etc, and then most likely go extinct (maybe not completely) themselves.
But if there's a reasonable chemical pathway to fixing nitrogen on a cold world, then that could be averted. It's probably possible, maybe it simply requires some interesting arrangement of metal ions, which should be more possible in an ammonia-based world since ammonia readily dissolves more metals than water. It might require a source of high-energy photons, or enough lower-energy ones to power antenna complexes like those in oxygenic photosynthesizers.