Alien Atmospheres and Life For Scifi

[mikegarrison]

15 hours ago, kerbiloid said:

It's on the same turret with all main sensors, to reduce the signal time.

Yeah, probably. It makes sense that vision receptors need to be close to the brain in order to get the signal processing done as quickly as possible. But the whole thing doesn't really need to get stuck out on a neck. Lots of Earth species basically have no neck.

[Piscator]

Well, being able to reposition your sensory organs quickly and energy-efficiently has its advantages, especially for a species which relies on vision heavily but also has a rather narrow field of view.

[kerbiloid]

40 minutes ago, mikegarrison said:

Lots of Earth species basically have no neck.

The monkeys have to cowardly crawl on branches and extend the sensitive turret between the leaves to see, if there is something to steal or somebody to get afraid of.

The headneck is a monkey periscope.

The brave cats operate same way.

[KSK]

My personal appendix nearly killed me (as in, I narrowly missed having it burst inside me) and I haven’t suffered for it ‘s absence since. 

I know - the plural of anecdote isn’t data - but it does seem to be an organ with significant downsides that we can happily live without.

I liked the rest of your post though and would add that your comment about metabolic pathways could also apply to the genetic code

Would alien genetic material be stored on a double-stranded polymer? Quite possibly -  they’re relatively stable, convenient to read out and their macrostructure can be largely uncoupled from their microstructure*

Would an alien genetic code be based on four monomers arranged in groups of three? Possibly - because that allows a reasonable number of coding units plus redundancy.

Would an alien genetic code be based on DNA with the same codons encoding the same amino acids? Much less likely in my opinion. 
 

* DNA - double stranded, doesn’t much matter what the primary structure (nucleotide sequence) is - the secondary structure will be a double helix. RNA - single stranded, secondary structure very dependent on primary structure.

[JoeSchmuckatelli]

19 minutes ago, KSK said:

Would an alien genetic code be based on DNA with the same codons encoding the same amino acids?

If I were a betting man, I would say yes. Merely because of the efficiency, flexibility and redundancy. Like water, life tends to take the path of least resistance and then fill in all the nooks and crannies 

DNA is a fundamentally simple system that can create complex things - why do it any other way? 

Edited October 28, 2021 by JoeSchmuckatelli

[kerbiloid]

After having a look at the terrestrial DNA nucleobases, I would doubt very much that the alien ones differ from those four very much.

Of course, it's technically possible, but it looks like these four are the simplest and most primitive nucleojunk at all,  so most probably they will be the first candidates for a wannabe-life.

[KSK]

4 hours ago, kerbiloid said:

After having a look at the terrestrial DNA nucleobases, I would doubt very much that the alien ones differ from those four very much.

Of course, it's technically possible, but it looks like these four are the simplest and most primitive nucleojunk at all,  so most probably they will be the first candidates for a wannabe-life.

Yeah, that's the big question. It's quite possible to make DNA analogues using non-natural nucleobases but whether those nucleobases would arise spontaneously...? I don't know. Maybe it's DNA or bust because that's just how  prebiotic chemistry works.

The genetic code though, I'm struggling to see as anything but arbitrary. Why does TTT code for phenylalanine but CTT code for leucine?  Was it chemically inevitable for an enzyme to evolve that couples leucine to that specific tRNA? Or was that just how things happened to turn out on Earth, and somewhere out there is a planet with DNA/RNA based life, in which TTT codes for leucine and not CTT?

For that matter, why do codons have three bases? Again, one answer is that it allows for 64 unique  sequences (assuming you always read them in the same direction), which is a good balance between coding for enough amino acids to make a diverse set of proteins, whilst allowing for enough redundancy that mutations don't automatically muck things up.  

On Earth, that's worked pretty well.  But maybe on a planet which suffers from higher radiation exposure, (or other environmental factors that lead to a higher mutation rate),  life is based on DNA again but with 4 bases per codon, to allow for much more redundancy to guard against that higher mutation rate.

This is all pure speculation of course and the kind of thing that reasonable people could reasonably disagree about. For that matter, it may never be scientific speculation (in the falsifiable Popper sense), so is it something we should even be discussing on a science and spaceflight forum?  

Edited October 28, 2021 by KSK

[Piscator]

The storage of genetic information is actually an area in which I would see a lot of room for diversity.

You would likely need some kind of polymer made of pretty much the same chemical elements as DNA (as those are the most available und useful for this purpose) but after that, all bets are off in my opinion. After all, even earth life commonly uses two types of  macromolecule with slightly different backbones and bases (DNA and RNA) and apparently it's not so rare to find bases other than the five regular ones in nature. (It seems even artificial ones have been successfully created and introduced into gene sequences.)  If you consider that there are about 30 variations of the genetic code as well, it seems highly unlikely that life of extraterrestrial origin would use a system that would closely resemble ours. There seems to be too much room for variation.

[JoeSchmuckatelli]

Wouldn't we be immune to alien life supporting planet's viruses if not DNA based? 

(also - if they're not DNA based... Wouldn't they be immune from us eating them?) 

OTOH the common cold on Antares IV could be a flesh eating bone jellying disease in humans 

Edited October 29, 2021 by JoeSchmuckatelli

[kerbiloid]

30 minutes ago, JoeSchmuckatelli said:

Wouldn't we be immune to alien life supporting planet's viruses if not DNA based? 

We should not try try eating or smoking them, because regardless of genes, they can accumulate their excretes which they accumulate all life long like the seafood and the desert crawling snacks do.

30 minutes ago, JoeSchmuckatelli said:

Wouldn't they be immune from us eating them?

Nothing personal, but can't understand... Are you at the human side or just interesting?

30 minutes ago, JoeSchmuckatelli said:

OTOH the common cold on Antares IV could be a flesh eating bone jellying disease in humans 

It is.

That's just why the first phase of a proper terraforming is called "Deionization exposure".

The second phase is "Rapid field paleontology."

Edited October 29, 2021 by kerbiloid

[tomf]

25 minutes ago, JoeSchmuckatelli said:

Wouldn't we be immune to alien life supporting planet's viruses if not DNA based? 

(also - if they're not DNA based... Wouldn't they be immune from us eating them?) 

OTOH the common cold on Antares IV could be a flesh eating bone jellying disease in humans 

Human Viruses are beautifully engineered things for entering human cells. Most viruses only infect a very small range of creatures and jumping species is pretty rare despite the fact all vertebrates are pretty much indistinguishable biochemically speaking.

So the idea that an alien virus equivalent would be able to in any way thrive inside us is laughable. 

Alien bacteria might be able to do a little better but still would be massively outcompeted by the bacteria that have evolved to use us as hosts.

Also the idea that alien life would use DNA seems very myopic, most life on earth doesn't use DNA.

[JoeSchmuckatelli]

2 hours ago, tomf said:

Also the idea that alien life would use DNA seems very myopic, most life on earth doesn't use DNA

Ummmm....

Please list examples of living organisms that have no DNA, especially anything cellular and able to reproduce. 

Thanks 

2 hours ago, kerbiloid said:

you at the human side or just interesting

Oh - sorry to confuse.  No, I don't want to eat any foreign sentient - but any space-cow or other non-sentient should be fair game. 

Antares IV isn't going to be any fun if the only thing we can eat are pigs and chickens imported from Earth.  I want to be able to hunt the fabled bugblatter beast and share its steaks with my friends... 

Don't you? 

[sevenperforce]

On 10/26/2021 at 4:43 AM, Codraroll said:

Hey, an oxygen/methane atmosphere might work decently enough until a spark is ignited. From that point on, the planet might not be entirely conducive to life for very long, though.

You’re killing me.

Not unlike an oxygen-methane atmosphere. 

[sevenperforce]

But, in all seriousness, life is going to evolve based on what is available to it on a given planet. What is available to it will depend on the abiotic chemistry of the planet. The abiotic chemistry of any planet will depend on the constituent elements in the protostellular nebula from which the planet coalesced.

Since the constituent elements in most protostellar nebulae will be fairly consistent across star systems and across galaxies, our own solar system is as good a place as any to look for available abiotic chemistry.

So you’re stuck with carbon, silicon, oxygen, hydrogen, calcium, sodium, iron, and nitrogen. Everything else is a rounding error.

[mikegarrison]

6 minutes ago, sevenperforce said:

So you’re stuck with carbon, silicon, oxygen, hydrogen, calcium, sodium, iron, and nitrogen. Everything else is a rounding error.

A lot of "rounding errors" are necessary for human life.

[JoeSchmuckatelli]

I'm not so sure.  Life seems to code for Luck.  Every hunter knows this. 

I think it's probably inevitable that any place that supports life long enough ends up with an efficient, intelligent species walking about. 

Reason being - if you are smart, you can tip the scales of luck just enough to matter... And given time, that matters a lot. 

[kerbiloid]

6 hours ago, JoeSchmuckatelli said:

9 hours ago, kerbiloid said:

you at the human side or just interesting

Oh - sorry to confuse.  No, I don't want to eat any foreign sentient - but any space-cow or other non-sentient should be fair game. 

I meant the opposite as you asked if the humans are edible for aliens after the discussion if the aliens are edible for humans, lol.

6 hours ago, JoeSchmuckatelli said:

Antares IV isn't going to be any fun if the only thing we can eat are pigs and chickens imported from Earth.  I want to be able to hunt the fabled bugblatter beast and share its steaks with my friends... 

Have you tried consuming roaches and mealworm, who are much closer to us? Why the extraterrestrial cattle could be more appetite? Have a look at the HalfLife creatures.
Terrestrial berries and mushrooms are full of surprises.

Do Australians eat koalas and platypuses? They are mammals (both koalas and Australians). 
Even a koala is closer to an Australian than a bullsquid from Xen. But they herd sheep.

The edibility means the possibility of metabolic interaction, and the toxicity means the same. 

So, the extraterrestrial life would be as edible as an unknown caterpillar sitting on unknown mushroom in a pool of unknown slime.
There are chances that they are edible, but better use them to make compost and grow normal human food, or sterilize the planet with gamma before usage.

The Australia is an example of why unlikely you would want to eat the fabled bugblatters, and what a terraforming should be.

5 hours ago, mikegarrison said:

A lot of "rounding errors" are necessary for human life.

Just because it is here and required in minor amounts. Otherwise other minor components would be used in metabolism.

4 hours ago, JoeSchmuckatelli said:

I think it's probably inevitable that any place that supports life long enough ends up with an efficient, intelligent species walking about. 

If it has enough time to evolve.

The Earth life is ~3 500 My old, and something complex is just 300 My. The modern top of species (which has replaced the older ones, more primitive and less effective) ~5 My.

It's about 50 My to problems with heat balance (due to the Sun evolution), about 500 My till life extermination due to overheating, ocean evaporation (so, greenhouse effect and water salinity), and oxygen excess (when the iron oxide of the upper core and mantle decays into iron and oxygen), about 1 500 My till geological death of the Earth and its magnetosphere, about 6 000 till the maximum Sun radius.

So, the Earth life progress bar is somewhere at 90..95% mark, its complex life occupies just its last 10% (from 85% mark), the modern life is just 0.1% of the whole life history of the Earth.

If the life appeared 300 mln years later, unlikely it had enough time to ever evolve into something more complex than jellyfishes.

And that's also a sentence to death for any kind of life in cooler conditions, as chemical reactions are much slower at lower temperatures.
So, nothing but colored protobacterial films on the stones of ice could be found on Titans and Plutos or near the stars other than yellow dwarves like this one.

Edited October 30, 2021 by kerbiloid

[mikegarrison]

5 hours ago, JoeSchmuckatelli said:

I think it's probably inevitable that any place that supports life long enough ends up with an efficient, intelligent species walking about. 

That's very human-centric.

Our ecological niche is cognition. So of course we think that cognition is the end-state of evolution. However, there are plenty of species just on this planet alone that have lasted a lot longer than humans without going into that cognitive niche, and it seems likely that when humans are gone there will probably be plenty of non-cognitive species still around.

[kerbiloid]

15 minutes ago, mikegarrison said:

Our ecological niche is cognition. So of course we think that cognition is the end-state of evolution. However, there are plenty of species just on this planet alone that have lasted a lot longer than humans without going into that cognitive niche, and it seems likely that when humans are gone there will probably be plenty of non-cognitive species still around.

The cognition allows to quickly adapt the surrounding medium to the body rather than vice versa, so there is no need in changing body every time when a climate changes, and it gives the ability to inhabit various (almost all possible) climatic zones.
Also it gives the ability to predict the deadly events and to avoid them before it happens.

The alternative is a zerg rush of short-living primitive species, to let the evolution adapt their bodies until some local cataclysme put them into a dead end when then they can't evolve enough fast.

Also the cognition gives the ability to manipulate with energy, collect and release a lot of energy at once (by fire, by water wheels, by plugging a pack other animals in one carriage), and concentrate the released energy in a small exact location (by using sharp or hot tools).

The cognition allows to quickly exchange with expirience, including the expirience of the people who had gone long away, so to avoid endless repeatable experiments.

So, as we can see, all major species evolve into the high complexity direction (and thus, better cognition), and the humans have 8 billions of 70 kg heavy species living in average fo r 70 years.

Almost no other kind has the same.

[KSK]

7 hours ago, sevenperforce said:

But, in all seriousness, life is going to evolve based on what is available to it on a given planet. What is available to it will depend on the abiotic chemistry of the planet. The abiotic chemistry of any planet will depend on the constituent elements in the protostellular nebula from which the planet coalesced.

Since the constituent elements in most protostellar nebulae will be fairly consistent across star systems and across galaxies, our own solar system is as good a place as any to look for available abiotic chemistry.

So you’re stuck with carbon, silicon, oxygen, hydrogen, calcium, sodium, iron, and nitrogen. Everything else is a rounding error.

Phosphorus too? That turned out to be pretty important for life here.

It’s also a nice illustration of your point that life will evolve using what’s available given that phosphate groups are key to metabolism (ATP), holding genetic material together, cell signalling (second messengers plus protein phosphorylation in general), skeletal structure (calcium phosphate), and wear resistant surfaces for teeth (apatite).

For that matter, the first three make your point even more loudly: adenosine monophosphate being a component of DNA, adenosine triphosphate being the ATP mentioned above and cyclic adenosine monophosphate being a key second messenger in signal transduction. Plus cyclic guanosine monophosphate of course, another repurposed DNA component used for a second messenger.

I love biochemistry. It’s full of these kinds of repurposed bits and pieces. 

Edited October 30, 2021 by KSK

[tomf]

9 hours ago, JoeSchmuckatelli said:

Ummmm....

Please list examples of living organisms that have no DNA, especially anything cellular and able to reproduce. 

I may have been taking a loose definition of life and I can't find the source I thought I had read that says that DNA organisms are outnumbered significantly by RNA viruses

[JoeSchmuckatelli]

8 hours ago, mikegarrison said:

That's very human-centric

Not particularly... I wrote that life codes for luck

Smarts allows the critter to tip the scales - in other words to be more efficient than other competing critters and thus survive and thrive

8 hours ago, kerbiloid said:

The cognition allows to quickly adapt the surrounding medium to the body rather than vice versa

 Yup 

Edited October 30, 2021 by JoeSchmuckatelli

[JoeSchmuckatelli]

6 hours ago, tomf said:

... I thought I had read that says that DNA organisms are outnumbered significantly by RNA viruses

That may be true - but if you recall, RNA works with DNA.  They're kind of a feature of the same system 

8 hours ago, mikegarrison said:

That's very human-centric

 

1 hour ago, JoeSchmuckatelli said:

I wrote that life codes for luck

There is a possibility that my view is 'modern-centric' as I'm certain that life codes for luck currently.  However, for a very long time life seemed to code for size, and some almost impossibly large creatures stomped around the planet with exceptional success. 

I presume that life also coded for luck during the period - but it may have been less important than sheer size during the age of dinosaurs... And then, abruptly, those that were lucky survived the unexpected catastrophe to bring in the modern age 

[mikegarrison]

2 hours ago, JoeSchmuckatelli said:

Smarts allows the critter to tip the scales - in other words to be more efficient than other competing critters and thus survive and thrive

No, you are still doing it.

Humans are very impressed with the power of the cognitive niche. Why? Because it is our niche. We think it's the best. We can barely imagine it as not being the ultimate in evolution. After all, it led to us! We thrive because of it!

But is it necessary in order to thrive? Alligators are not very impressed with cognition. They have been around a lot longer than us, and may well be around a lot longer than us. They have never nuked themselves. They have never filled their own drinking water with toxic waste. They don't kill themselves by drinking and driving.

Sure, alligators could never have gotten themselves to the moon or climbed Mount Everest or spread themselves from the North Pole to the South Pole, but so what?

Do we obsess about the search for extra-terrestrial swamp reptiles? No. But we do obsess about searching for extra-terrestrial intelligence. And why? Because that's our niche. That's our thing. So we think it's the best. So we think life elsewhere *must* develop it in order to really be successful.

It's human-centric thinking.

Edited October 30, 2021 by mikegarrison

[KSK]

As with many things, Douglas Adams nailed it.

“For instance, on the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much—the wheel, New York, wars and so on—whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man—for precisely the same reasons.”