Most efficient ways to conquer earth

[RocketSquid]

2 hours ago, kerbiloid said:

One tick of geological clock. It just still hasn't got extinct.

If it was still alive abillion years later, that should mean abscence of progress.

What are evolutionary perspectives of this bacteria?

It’s very likely that it will outlive all other life on earth, and a similar bacteria could easily serve as the food source for an ecosystem.

[kerbiloid]

1 minute ago, RocketSquid said:

It’s very likely that it will outlive all other life on earth

Why such conclusion? Are there a lot of other survivors in the deep underground?

[RocketSquid]

3 minutes ago, kerbiloid said:

Why such conclusion? Are there a lot of other survivors in the deep underground?

We don’t know. It’s very rare for humans to go that deep. However, its environment is incredibly stable.

[kerbiloid]

1 minute ago, RocketSquid said:

We don’t know. It’s very rare for humans to go that deep. However, its environment is incredibly stable. 

Then they come back...

Spoiler

 

[JERONIMO]

bomb em' kill em' get em'

Edited June 6, 2019 by JERONIMO

[Guest]

5 hours ago, kerbiloid said:

What are evolutionary perspectives of this bacteria?

For this particular one? It's pretty well optimized for where it lives, it doesn't need to evolve. It can't expand into other environments because other life is already there. If it was alone on Earth, it could kick-start a whole biosphere after less than a billion years. This is actually a fairly advanced organism. 

BTW, this is one reason why you don't need "plants" to have fungi (I missed your earlier wall of text and I don't feel like going back to it now). They can feed on remains (or living colonies, which is annoying if you're trying to grow anything that isn't fungus) of bacteria and archea. Plants are actually quite finicky, for primitive biospheres you get mostly algae and lichens... which are a combination of algae and fungi. 

Edited June 6, 2019 by Guest

[kerbiloid]

6 hours ago, Dragon01 said:

For this particular one? It's pretty well optimized for where it lives

We may congratulate her _{(even when its optimization degree is declared arbitrary, maybe it's getting extinct)}, but...

6 hours ago, Dragon01 said:

it doesn't need to evolve

... but we are speaking about evolution, not about the bacteria comfort.

(Though, I can't see why such conclusion.
Nobody needs to evolve, everybody is doing this forcedly).

And as we can see (in Russian wiki) it divides once per 28 hours (not 20 minutes like a nice, well brought-up bacteria.), so anyway its evolution is a hundred times slower.

Also such slow replication should make her adaptation abilities poor if when the conditions change, but this doesn't matter, as it anyway won't become something bigger.

7 hours ago, Dragon01 said:

If it was alone on Earth, it could kick-start a whole biosphere after less than a billion years.

And as its generations get replaced 100 times slower, 10 bln years of its evolution is like just 100 mln of a normal bacteria evolution.

7 hours ago, Dragon01 said:

This is actually a fairly advanced organism. 

This is a puny outsider which tries to survive.
Any other bacteria will eat them on breakfast if meet. Any depletion of the local hot water will kill it. Any depletion of local radioactive isotopes will kill it. A short-living big star will burn them as well.

7 hours ago, Dragon01 said:

this is one reason why you don't need "plants" to have fungi (I missed your earlier wall of text and I don't feel like going back to it now). They can feed on remains (or living colonies, which is annoying if you're trying to grow anything that isn't fungus) of bacteria and archea.

If this bacteria reproduces once per 28 h, the fungi don't have too much food to eat, and should reproduce much slower than this bacteria.
Probably that's why we can see no fungi aside of it.

7 hours ago, Dragon01 said:

Plants are actually quite finicky, for primitive biospheres you get mostly algae and lichens... which are a combination of algae and fungi. 

Algae are plants, are you aware?

Plants are mostly the organisms utilizing the solar energy, it's much better source of it than radioactive decay.

[RocketSquid]

5 minutes ago, kerbiloid said:

We may congratulate her _{(even when its optimization degree is declared arbitrary, maybe it's getting extinct)}, but...

... but we are speaking about evolution, not about the bacteria comfort.

(Though, I can't see why such conclusion.
Nobody needs to evolve, everybody is doing this forcedly).

And as we can see (in Russian wiki) it divides once per 28 hours (not 20 minutes like a nice, well brought-up bacteria.), so anyway its evolution is a hundred times slower.

Also such slow replication should make her adaptation abilities poor if when the conditions change, but this doesn't matter, as it anyway won't become something bigger.

And as its generations get replaced 100 times slower, 10 bln years of its evolution is like just 100 mln of a normal bacteria evolution.

This is a puny outsider which tries to survive.
Any other bacteria will eat them on breakfast if meet. Any depletion of the local hot water will kill it. Any depletion of local radioactive isotopes will kill it. A short-living big star will burn them as well.

If this bacteria reproduces once per 28 h, the fungi don't have too much food to eat, and should reproduce much slower than this bacteria.
Probably that's why we can see no fungi aside of it.

Algae are plants, are you aware?

Plants are mostly the organisms utilizing the solar energy, it's much better source of it than radioactive decay.

Any other bacteria will eat them for breakfast, but a) that's how ecosystems work and b) it's in an environment highly hostile to other bacteria. And it can in fact survive depletion of local hot water, by encysting and waiting for there to be more. Depletion of local radioactive isotopes will reduce available energy but not remove it altogether. 

Whether or not algae are plants is up for debate depending on how narrow you choose to make the category of plant. However, cyanobacteria are commonly called blue-green algae even though they aren't technically algae, and most certainly aren't plants. These were most likely what Dragon01 was referring to. Lichens can hold true algae, cyanobacteria, or both. While cyanobacteria are somewhat less efficient at photosynthesis and need more water, they partially make up for this with their ability to fix nitrogen. Lichens can also survive in the vacuum of space with no reduction in reproductive ability, so it's safe to say they're quite hardy.

And lastly, I'm not sure you get the point of bringing up the radiation as a source. It's not to suggest that it would be the basis of an ecosystem when sunlight is available. It's to suggest that an ecosystem can exist without sunlight, at least not sunlight in the conventional sense. 

[kerbiloid]

1 minute ago, RocketSquid said:

Any other bacteria will eat them for breakfast, but a) that's how ecosystems work and b) it's in an environment highly hostile to other bacteria.

So, we may conclude that this environment is not life-friendly. Otherwise they already would be eaten.
This in turn limits the perspective of its further evolution.

3 minutes ago, RocketSquid said:

And it can in fact survive depletion of local hot water, by encysting and waiting for there to be more.

For a million years? Geological processes are slow.

Why we can see only one such bacteria? Why not a whole bunch of their species? They had 4 billion years to adapt.
I have a bad feeling that all previous attempts have finished very soon. Why this one shouldn't?

4 minutes ago, RocketSquid said:

However, cyanobacteria are commonly called blue-green algae even though they aren't technically algae, and most certainly aren't plants. These were most likely what Dragon01 was referring to. Lichens can hold true algae, cyanobacteria, or both. 

We may give to cyanobacteria any passport we want (they even will not be aware), but OK - replace the "plant" with "photosynthetic organism", does it change something?

8 minutes ago, RocketSquid said:

Lichens can also survive in the vacuum of space with no reduction in reproductive ability, so it's safe to say they're quite hardy.

Lichens can just die slowly in vacuum, they can't live there.

9 minutes ago, RocketSquid said:

It's to suggest that an ecosystem can exist without sunlight, at least not sunlight in the conventional sense. 

Of course it can. The original Earth life was doing this even without radiation.

But without the sunlight it will stay just microbes.

[Guest]

5 hours ago, kerbiloid said:

Why we can see only one such bacteria? Why not a whole bunch of their species? They had 4 billion years to adapt.
I have a bad feeling that all previous attempts have finished very soon. Why this one shouldn't?

We can see only one because we don't dig that deep very often. The interior of the Earth, and the bottom of its oceans, is less well explored than outer space. Digging is much harder than looking up. Those bacteria were found in the deepest mine on Earth. There is a number of other mines of similar depth, they might be something interesting in them, as well.

Quote

Lichens can just die slowly in vacuum, they can't live there.

They die slowly in atmosphere, too. So do you. A lichen could probably live longer in vacuum than you can on Earth. But it doesn't matter, since we're not talking specifically about living in a vacuum. They can also live (and thrive!) in very polluted areas, in cities and the like. Lichens in general are incredibly hardy.

Quote

For a million years? Geological processes are slow.

We have no way to run an experiment like that, but I don't see why not. Dried, encysted forms are very sturdy. 

Quote

So, we may conclude that this environment is not life-friendly. Otherwise they already would be eaten.
This in turn limits the perspective of its further evolution.

Of course its not life-friendly. But that does not limit its perspectives in any way. Other life does. As it is, this bacteria has nowhere to expand.

Quote

We may congratulate her _{(even when its optimization degree is declared arbitrary, maybe it's getting extinct)}, but...

You don't seem to know how evolution works. Mathematically, evolution is a random walk where only the steps that preserve or increase the "fitness" parameter lead to further steps. Once the fitness function reaches a maximum, evolution can't take you further. If it's a local maximum (that is, not super-well adapted, but there's no immediate way to improve), you can sometimes "jump" out of it by a lucky, large mutation, but when it's a global (not in "for the entire Earth" sense, but for the entire function in a given environment) maximum, it can't happen. 

For this bacteria, given the amount of energy and physical space available, this is really the best form. Consider that it is a bacterium, while other organisms living in similar environments are archea. That alone gives it a huge advantage. If it had access to another environment that it could colonize, it would eventually do so - but it can't, because there are other things in place already. If there weren't, its descendants would take their place in a few million years. 28 hour cycle is actually reasonably fast, and if given access to more energy, one of the first things to evolve would be faster division. You're getting far too hung up on things taking longer than we're used to.

Edited June 7, 2019 by Guest

[kerbiloid]

13 minutes ago, Dragon01 said:

We can see only one because we don't dig that deep very often. The interior of the Earth, and the bottom of its oceans, is less well explored than outer space. Digging is much harder than looking up. Those bacteria were found in the deepest mine on Earth. There is a number of other mines of similar depth, they might be something interesting in them, as well.

If there was something significant, it would be already found in the miners' lungs.

Science operates with facts. Currently they are: just one such species is found, it's young, it reproduces very slowly, it came from much better place above, it lives in conditions which almost exclude its further evolution into something valuable.

25 minutes ago, Dragon01 said:

They die slowly in atmosphere, too.

Lichens live in atmosphere, it's normal for them. In vacuum they don't produce anything without the air.

29 minutes ago, Dragon01 said:

A lichen could probably live longer in vacuum than you can on Earth.

Just a demagogy. Lichens don't grow, don't replace their generations in vacuum.
A specimen of a lichen can survive in vacuum for a while, but a lichen species can proceed its existance there.

32 minutes ago, Dragon01 said:

They can also live (and thrive!) in very polluted areas, in cities and the like.

One's trash is another one's treasure. Pollution is absolutely not the thing here, it's just alternative form of resources.

34 minutes ago, Dragon01 said:

We have no way to run an experiment like that, but I don't see why not.

We can see the only experiment lasting much less than a billion years (because these mines and mountains are much younger).

35 minutes ago, Dragon01 said:

Dried, encysted forms are very sturdy. 

Dried, encysted forms do not evolve. Good luck for them in their surviving for 10 billion years, but they are nothing as a complex form of life we discuss.

36 minutes ago, Dragon01 said:

Of course its not life-friendly. But that does not limit its perspectives in any way

Currently in obviously does, as we can observe the only example. If you find more, this will make a revolution in biology, I guess.

38 minutes ago, Dragon01 said:

You don't seem to know how evolution works. Mathematically, evolution is a random walk where only the steps that preserve or increase the "fitness" parameter lead to further steps. Once the fitness function reaches a maximum, evolution can't take you further. If it's a local maximum (that is, not super-well adapted, but there's no immediate way to improve), you can sometimes "jump" out of it by a lucky, large mutation, but when it's a global (not in "for the entire Earth" sense, but for the entire function in a given environment) maximum, it can't happen. 

That's how "genetic algorithms" work. There is no single fitness function in rreal nature, and the sampling size is always limited.

40 minutes ago, Dragon01 said:

For this bacteria, given the amount of energy and physical space available, this is really the best form.

With 28 hours between generations it won't even notice being eaten.

41 minutes ago, Dragon01 said:

Consider that it is a bacterium, while other organisms living in similar environments are archea.

Btw, it became a bacteria not there, it's just imprisoned. So, in fact in those conditions it would stay an archea.
Where/when/how did the eucaryotes appear?

43 minutes ago, Dragon01 said:

 If it had access to another environment that it could colonize, it would eventually do so

Just starting the evolution from almost starting point. Why need this? We already have other bacteria already having done that.
 

[RocketSquid]

11 hours ago, kerbiloid said:

So, we may conclude that this environment is not life-friendly. Otherwise they already would be eaten.
This in turn limits the perspective of its further evolution.

For a million years? Geological processes are slow.

Why we can see only one such bacteria? Why not a whole bunch of their species? They had 4 billion years to adapt.
I have a bad feeling that all previous attempts have finished very soon. Why this one shouldn't?

We may give to cyanobacteria any passport we want (they even will not be aware), but OK - replace the "plant" with "photosynthetic organism", does it change something?

Lichens can just die slowly in vacuum, they can't live there.

Of course it can. The original Earth life was doing this even without radiation.

But without the sunlight it will stay just microbes.

We don’t just see one bacteria. We see one species of bacteria, composed of a large number of individuals. 

Lichen don’t die slowly in a vacuum, that would be accompanied by a loss of fitness on revival. They don’t die. They wait.

There’s no reason to think lack of sunlight limits it to microbes. We see a variety of multicellular organisms existing at hydrothermal vents in the deep sea.

[kerbiloid]

17 minutes ago, RocketSquid said:

We don’t just see one bacteria. We see one species of bacteria, composed of a large number of individuals. 

Everyone with its name, its fate, its character...

Obviously I mean the whole species, not an individual bacterial person.

20 minutes ago, RocketSquid said:

Lichen don’t die slowly in a vacuum, that would be accompanied by a loss of fitness on revival. They don’t die. They wait.

They wait for gas and water. If they get nothing - they die. Their time in vacuum lasts only while they have enough internal resources to spend, or while the vacuum slowly destroys their molecules.

22 minutes ago, RocketSquid said:

We see a variety of multicellular organisms existing at hydrothermal vents in the deep sea. 

Parasiting on the detrite falling from the ocean surface.

[Terwin]

44 minutes ago, kerbiloid said:

Parasiting on the detrite falling from the ocean surface.

Nope, their base calorie source is a type of bacteria(sulfur eating I think), and everything else feeds on those.

 

https://en.wikipedia.org/wiki/Hydrothermal_vent#Biological_communities

Edited June 7, 2019 by Terwin
adding wiki link

[Guest]

On 6/7/2019 at 5:48 PM, kerbiloid said:

They wait for gas and water. If they get nothing - they die. Their time in vacuum lasts only while they have enough internal resources to spend, or while the vacuum slowly destroys their molecules.

Wrong. They do not spend their internal resources while in vacuum (or indeed, if the weather is too dry. Water is the key here, not air. If you somehow hydrated them in orbit they could have trouble). Hence my comment, they could survive however long it took for them to end up in a place where they could grow. Vacuum does nothing to destroy their cells. Oh, and they are also really resistant to radiation. In fact, they are good panspermia candidates, the only part of this hypothesis that has not yet been proven possible is their ability to survive reentry. And that is mostly because nobody has come up with an experiment to test it that wouldn't involve lifting a huge rock with lichens in it into orbit and dropping it back down, which is difficult to get funding for.

On 6/7/2019 at 1:03 PM, kerbiloid said:

That's how "genetic algorithms" work. There is no single fitness function in rreal nature, and the sampling size is always limited.

For a given, isolated environment, a single fitness function is a very good approximation. It gets complicated when you introduce competing species and exchange with other ecosystems, but at its core, evolution is an implementation of a kind of genetic algorithm (where do you think they got their name?). 

On 6/7/2019 at 1:03 PM, kerbiloid said:

Just starting the evolution from almost starting point. Why need this? We already have other bacteria already having done that.

Not "almost from the starting point". Bacteria like this one are, in fact, quite far up the evolutionary ladder. If you put it on another planet where there's no other life and the conditions are suitable for it to live, it would only take it a few million years to colonize it, evolving ways to take advantage of available energy and carbon sources. Now, we don't know how such a system would develop further, but it's almost certain it would develop. This is why sterilization of spacecraft is so important, BTW. 

I believe everything else has been sufficiently addressed by others. And besides, we're talking about life on Earth. The original point was, in case you don't remember, that life evolving on other planets, in different conditions, would definitely not produce forms resembling the ones we know from Earth, except maybe in a very superficial way. With such variety on just one planet, and evolution being mostly based on random mutations and/or random recombination, it's a bit silly to expect that any life we find outside Earth to look familiar. Extraterrestrial life, no matter what form it takes, is going to be utterly bizarre.

Edited June 8, 2019 by Guest

[kerbiloid]

6 hours ago, Dragon01 said:

Wrong. They do not spend their internal resources while in vacuum (or indeed, if the weather is too dry. Water is the key here, not air.

Surprise! There is no water in vacuum, too.
In vacuum they have only... er... vacuum.

6 hours ago, Dragon01 said:

If you somehow hydrated them in orbit they could have trouble).

Wow... We are now seriously discussing a spontaneous generation of a magically hydrated orbital life in vacuum in a close proximity of an unstable source of red light with varying luminosity... Well, well..

Or is it about the life evolution on the Moon?

6 hours ago, Dragon01 said:

Hence my comment, they could survive however long it took for them to end up in a place where they could grow.

1. Any facts?
2. How at all is it related to the life evolution, leave alone the occupation of Earth?

7 hours ago, Dragon01 said:

Vacuum does nothing to destroy their cells.

Vacuum does everything to destroy their cells at least because of the pressure difference, the evaporation, and the cooling by evaporation.

7 hours ago, Dragon01 said:

For a given, isolated environment, a single fitness function is a very good approximation.

This may be a surprise again, but in real life the species survivability is being tested in numerous ways simultaneously.
So, yes, they have a fitness function: does their population grow, or not. So, what?

7 hours ago, Dragon01 said:

genetic algorithm (where do you think they got their name?)

They got their name from a mathematician who believed that what he had invented is not just the good old method of Monte-Carlo with bells and whistles.

It's a pity he was not a Warcraft player, otherwise instead of the "genetic algorithms" we would have "warcraft algorithms" with functions named after orcs, elves, and goblins.
At least, it would be much funnier, though still Monte-Carlo.

7 hours ago, Dragon01 said:

Bacteria like this one are, in fact, quite far up the evolutionary ladder.

1. Why are they farther up the evolutionary ladder than any other bacteria?
2. They can't use the most common sources of energy and chemistry on the Earth: the sunlight and the oxygen. They need quite rare set of resources and live only in the deepest mines.
A mine or a cave depth doesn't exceed 1.5 km in the Earth gravity, and there is quite few of such deep mines and caves.
So, they are just an exhaust of evolution, not its advance.

7 hours ago, Dragon01 said:

If you put it on another planet where there's no other life and the conditions are suitable for it to live, it would only take it a few million years to colonize it, evolving ways to take advantage of available energy and carbon sources.

1. Or get extinct in after a millenia.
2. Nobody puts it on another planet. It should appear there itself. Interesting, how, if here on the Earth it has evolved from usual bacteria from the ocean. And it can't consume the visible light, so is by definition a poor colonizer. Like an Australian coala eating only eucalypt leaves trying to colonize Canadian forests.
3. Also it's very interesing to see how can it evolve into something more multicellular than bacteria, to be not just a film of slime on a stone.

7 hours ago, Dragon01 said:

The original point was, in case you don't remember, that life evolving on other planets, in different conditions, would definitely not produce forms resembling the ones we know from Earth, except maybe in a very superficial way.

If these "different condinitons" can produce any complex life at all.

7 hours ago, Dragon01 said:

With such variety on just one planet, and evolution being mostly based on random mutations and/or random recombination, it's a bit silly to expect that any life we find outside Earth to look familiar. Extraterrestrial life, no matter what form it takes, is going to be utterly bizarre.

With such variety on just one planet we can see that only one evolutionary tree, in most cases exactly matching the most common resources and conditions: water, oxygen, 600 nm light.
And as we can see, nothing bigger than yellow dwarf can have its own complex life, and everything smaller than a yellow dwarf can provide the life with dramatically more poor resources and conditions.
So, we can surely reserve "1%" of probability for a "random local freak show", and presume that "99%" of chances arre that a complex life can evolve only in conditions similar to the Earth.

[brookerogers]

Create a virus that will wipe out all the human life except you.

[kerbiloid]

13 minutes ago, brookerogers said:

Create a virus that will wipe out all the human life except you.

Too easy.

[Spacescifi]

4 minutes ago, kerbiloid said:

Too easy.

 

In practice? Requires patience. How can you create a virus without a working knowledge of human anatomy?

Aliens won't know this from the beginning. It may take years of study, and even then the human immune system tends toward becoming immune, which us one reason why diseases have not wiped us out totally already.

[kerbiloid]

6 minutes ago, Spacescifi said:

How can you create a virus without a working knowledge of human anatomy?

https://en.wikipedia.org/wiki/Plague_Inc.

[Guest]

On 6/9/2019 at 6:36 AM, kerbiloid said:

Surprise! There is no water in vacuum, too.
In vacuum they have only... er... vacuum.

Wow... We are now seriously discussing a spontaneous generation of a magically hydrated orbital life in vacuum in a close proximity of an unstable source of red light with varying luminosity... Well, well..

Or is it about the life evolution on the Moon?

You're missing the point. I was explaining the mechanism by which they survive. They survive by being dehydrated. Which makes them immune to almost everything. If you want more "facts" than that (I assume you mean "sources". All that I said is based on actual research results), go look in your local university. Here's one article that comes to mind: de Vera JP, Horneck G, Rettberg P, Ott S (2004). "The potential of the lichen symbiosis to cope with the extreme conditions of outer space II: germination capacity of lichen ascospores in response to simulated space conditions". Advances in Space Research. 33 (8): 1236–43.

I wouldn't expect this thing to be open access, though. If you know someone from MLU, then you maybe be able to get him/her to try to find someone or someplace where this paper could be accessed. MLU works with Roscosmos, so someone in there should have "Advances" on subscription.

Quote

Vacuum does everything to destroy their cells at least because of the pressure difference, the evaporation, and the cooling by evaporation.

Evaporation of what? Pressure of what? Because if you think "water", then you don't know what "dehydrated" means.

Quote

 "99%" of chances arre that a complex life can evolve only in conditions similar to the Earth.

OK, let's go with that, since you obviously have neither sufficient imagination nor actual knowledge of biology to come up with options for a radically different environment (even for something as simple as a red dwarf). Let's have life on a planet similar to Earth. Let's say it evolved, at some point, to produce oxygen as a side effect of their photosynthesizing (which is not certain to happen, but let's go with that), giving the planet an oxidizing atmosphere. The galaxy is big enough for at least one of your "Parallel Earth" worlds to be out there somewhere. Now, what makes you think that the solutions that life out there comes up with are going to be in any way similar to what life on Earth evolved? 

Even if you made an exact copy of Earth, life would probably turn out very different, because of how evolution works (which I explained, but I don't know if you understood). Every single little change from that gives you further deviation from what we see here. Indeed, Earth itself suffered several mass extinctions, and you may see just how much variation was there between pre- and post-extinction biosphere. Then consider that mass extinctions typically leave a few quite advanced organisms and don't "restart evolution" from bacteria.

Edited June 10, 2019 by Guest

[kerbiloid]

4 minutes ago, Dragon01 said:

They survive by being dehydrated. Which makes them immune to almost everything

So, sterile while they are immune.

5 minutes ago, Dragon01 said:

If you want more "facts" than that (I assume you mean "sources"

I mean, more than one such species, or numerous places with them. Wiki is enough good for me.
Otherwise they are an interesting artifact, nothing more.

7 minutes ago, Dragon01 said:

Evaporation of what? Pressure of what? Because if you think "water", then you don't know what "dehydrated" means.

While they are dehydrated, they can't reproduce, and thus evolve. They also can't repair cell damages.

9 minutes ago, Dragon01 said:

you obviously have neither sufficient imagination nor actual knowledge of biology to come up with options for a radically different environment (even for something as simple as a red dwarf).

That's true. I can't imagine a complex life evolved near a red dwarf. That's why I mention this "1%" chance as a "miracle".

11 minutes ago, Dragon01 said:

Let's say it evolved, at some point, to produce oxygen as a side effect of their photosynthesizing (which is not certain to happen, but let's go with that), giving the planet an oxidizing atmosphere.

What, in turn, should take several times more time than on Earth, due to the lower rate of photosynthesis.

13 minutes ago, Dragon01 said:

 The galaxy is big enough for at least one of your "Parallel Earth" worlds to be out there somewhere.

And almost everywhere the galaxy suffers from deadly radiation events either always, or often.
While the outer rim lacks elements heavier than hydrogen.
So, not so big is that galaxy, its habitable part.

16 minutes ago, Dragon01 said:

Now, what makes you think that the solutions that life out there comes up with are going to be in any way similar to what life on Earth evolved? 

For me, it's enough hard to invent a different way for species like worms, molluscs, and even arthropodes. Even fishes.
They are just a pipe with in/out ends. Of course, their inner organs may vary, but unlikely a lot.

More complex creatures of course may look different.

Spoiler

 

20 minutes ago, Dragon01 said:

Even if you made an exact copy of Earth, life would probably turn out very different, because of how evolution works (which I explained, but I don't know if you understood).

Poor, poor exotic species.
We had a lot of them even here, on the Earth. But look around. Just dull and pragmatiсally designed species survive: dogs/cats, cattle/horses, pigs, Their skeletons, being zoomed, look so similar, no exotic parts at all.

So, I have nothing against six-legged pigs with elephant ears, but unlikely it can be a speaking jelly pyramid with five eyes or a thinking Sargasso Sea.

[tater]

Start a tech company, then control what everyone is allowed to see and hear?

[Terwin]

52 minutes ago, kerbiloid said:

Poor, poor exotic species.
We had a lot of them even here, on the Earth. But look around. Just dull and pragmatiсally designed species survive: dogs/cats, cattle/horses, pigs, Their skeletons, being zoomed, look so similar, no exotic parts at all.

So, I have nothing against six-legged pigs with elephant ears, but unlikely it can be a speaking jelly pyramid with five eyes or a thinking Sargasso Sea.

Why are you so fixated on mammals?  They are just one small branch of life here on earth.

Many lizards can 'switch gears' between a slow and efficient waddling walk and a fast energy-intensive sprinting run by rotating their legs to either be beside them(waddle) or under them(sprint).

A fish skeleton looks nothing like a horse skeleton, even dolphins and whales have markedly different skeletons and they are still mammals.

Sharks don't even have rigid skeletons, using primarily cartilage instead.

Squid have 6 limbs, and octopus have 8, and neither has an internal skeleton.  Have you ever seen videos of a mimic octopus?  https://en.wikipedia.org/wiki/Mimic_octopus  those things can seem decidedly out of this world.

Centipedes have anywhere from 30 to 350 legs, and millipedes have more than twice that number.

Even incredibly common and successful insects like ants have 6 legs.

Not to mention jelly-fish, coral(including barnacles), flying fish, bats, flying squirrels, starfish, brittlestars, Birds, arachnids, and some truly wonky-looking stuff from the deep ocean.

All of those seem quite successful and are still around

Octopus are often considered among the most intelligent species on earth, and they look nothing like humans(and yes, they can leave the water for minutes at a time, so it would not be out of the question for them to eventually learn to smelt ores and other 'surface only' technologies, they are already known for opening screw-on lids and sneaking on to fishing boats to eat crabs).

 

[Spacescifi]

36 minutes ago, Terwin said:

Why are you so fixated on mammals?  They are just one small branch of life here on earth.

Many lizards can 'switch gears' between a slow and efficient waddling walk and a fast energy-intensive sprinting run by rotating their legs to either be beside them(waddle) or under them(sprint).

A fish skeleton looks nothing like a horse skeleton, even dolphins and whales have markedly different skeletons and they are still mammals.

Sharks don't even have rigid skeletons, using primarily cartilage instead.

Squid have 6 limbs, and octopus have 8, and neither has an internal skeleton.  Have you ever seen videos of a mimic octopus?  https://en.wikipedia.org/wiki/Mimic_octopus  those things can seem decidedly out of this world.

Centipedes have anywhere from 30 to 350 legs, and millipedes have more than twice that number.

Even incredibly common and successful insects like ants have 6 legs.

Not to mention jelly-fish, coral(including barnacles), flying fish, bats, flying squirrels, starfish, brittlestars, Birds, arachnids, and some truly wonky-looking stuff from the deep ocean.

All of those seem quite successful and are still around

Octopus are often considered among the most intelligent species on earth, and they look nothing like humans(and yes, they can leave the water for minutes at a time, so it would not be out of the question for them to eventually learn to smelt ores and other 'surface only' technologies, they are already known for opening screw-on lids and sneaking on to fishing boats to eat crabs).

 

 

I think kerboloid is pointing out that the real creatures we do have have the most efficient body design for the life style they lead.

One need not get bogged down in theories to make a design seem logical.

Just give a reason that makes the design optimal or necessary. Even if it would not be optimal on Earth, it should be optimal for an alien world designed for alien life.

Just as Earth is optimized for our kinds of life.

So the fictional aliens have six arms?  Well perhaps mostly all the vegetables and plants they eat only grows on trees and their fruits do not fall to the ground. Rather they rot where they grow until picked by a bird, animal, or sapient climbing alien.

Suddenly six arms seems reasonable.