I mean, if humanity goes extinct and it's another 65 million years before another intelligent species evolves, what evidence would they have of our existence? All our buildings would've long since crumbled into dust or been crushed by plate tectonics. Metal will corrode and rust away after a few thousand years. Our largest stone monuments will be gone after 10,000 or so. You'll find occasional fossilized skeletons, but all that would tell future species is that a bipedal mammal with a large brain once existed. Even plastics, the bane of environmentalists, degrade over a couple thousand years.
Probably the only thing we'd see would be a huge mass extinction and an unusually rapid change in the earth's climate. Which we've seen several times in the geologic record already.
If we make it for another few hundred years, not only will there be a mass extinction, but there will also probably be a traceable sudden explosion in a novel form of gene transfer and creation that can't be explained by any other theory. The modern fashionable self-loathing idea that we are a uniquely biodiversity-destroying organism may be merely a consequence of our current point of view; rather than "extinction" this could in fact be an inexplicable explosion in diversity if you could see 1000 years into the future. But of course the mass extinction will still be there. I haven't done an analysis but it may also be the case that the extinction has a very characteristic pattern; again, rather than the fashionable self-loathing model of "humans just destroy everything" it may be noticeable that fauna died out in favor of things that are clearly domesticated even just from their skeletons, and that human predators were preferentially extincted, etc.
Do keep in mind that diversity enables diversity. If biosphere complexity falls enough changes are it will never recover. Earth had live almost immediately after formation. It took more than 2.5B years for something more complex to emerge from the ur uni-cellular broth. Evolution or linear increasing complexity is not guaranteed by any means. What will a chimp bashing rocks in the bush be doing in 1000 000 years? Building quantum computers or bashing rocks. Overwhelming evidence points to bashing rocks.
Besides, I'd rather we risk ending up on the galactic buffet table for the chance of finding life forms we can "compare notes with". We're all going to die and go extinct regardless.
And it only takes one massively paranoid, xenophobic species lobbing big rocks at people to ruin the entire neighbourhood.
I don't think camouflaging necessarily means not leaving your gravity well, but if there's someone lobbing big rocks at potential threats, then the only ones exploring will be the ones powerful enough or good enough at hiding for us to be unlikely to spot them unless they want us to. Everyone else will be dead.
It's one of the more compelling answers to the Fermi paradox to me, while at the same time being profoundly depressing. But it's less depressing than the chance that there might not be any other civilizations.
"And it only takes one massively paranoid, xenophobic species lobbing big rocks at people to ruin the entire neighbourhood."
Ahh, Germany ...
I misplaced a link and the name of an author of a sci-fi novel in which space battles are much more science based than the usual laser-tag shoot off. I'll dig through my bookmarks and hopefully post the name in the reply when I get to my pc..
I think there was also a reddit thread about it sometimes in the past.
That's a rather significant difference to the proposed idea.
Similarly, maybe there's something missing from the Earth that we're just not thinking of because, well, you can't miss something if you never had it.
https://www.scientificamerican.com/article/mushroom-evolutio...
(Not asking critically - serious, I have no idea, do billions of people and whatever else we take down with us replenish what we've pulled out of the ground?)
Or would you then argue that intelligent life could develop sort of moratorium on further development in line with their value system?
I've also wondered how a race without something like a hand ever gets around to making complex tools with multiple moving parts. If Dolphins had twice the brain power that they do now, would they be able to build anything? The intelligence of other races may simply fail to be expressed in any way that is noticeable once they are gone. Hell dinosaurs might of been smarter than us and simply unable to use and create tools.
Given the constraints (earth located in our universe) of the probability space of physical interactions which produce life, I believe that our current state is the only possible state.
Our buildings are on dry land. Dry land is dry because it's predominantly made of continental crust [1]. It's lighter than oceanic crust [2]. When oceanic and continental crusts meet, the oceanic tends to get driven under the continental crust, which floats on top. Keep in mind that we still have fossil shells feom 65 million years ago.
The stuff on the moon will remain there for a very very long time, but until another civilization acquires the technological capability to explore a good amount of the moon's surface, it's doubtful they would stumble across the exact same spot as the Apollo landings.
But radionuclides are the ultimate signals. Palladium-107 is a byproduct of nuclear weapons use that becomes incorporated into palladium-bearing rocks and decays to silver, which can be detected by the presence of Ag-107 in palladium ores lacking other silver isotopes. Remaining Pd-107 can be used to estimate the date at which the palladium was deposited or the ore can be dated by its depth. So we can exclude the use of uranium-based nuclear weapons by previous inhabitants going back about... 60-80 million years since the half-life of Pd-107 is about 6 million years.
In theory we could have tried to detect whether nuclear weapons had been used on Earth in the last 120-150 million years by looking for iodine-129 in the oceans, but we already blew up too many bombs to confound that experiment. Finding iodine-129 some place we don't expect it would be interesting.
How intelligent is intelligent?
Homo Neanderthalensis predated Homo Sapiens by about 100,000 years. They were intelligent enough to build tools and have communities.
Oldest corvid fossils are 25 million years old[1]. They are known to be very intelligent and modern crows can solve 8-step puzzles, build tools, teach their young etc. etc.
I mean, intelligence has evolved independently many times in animals on earth. It's hard to say which species was first to become intelligent, but I'm pretty sure humans weren't the first.
[1] http://www.reed.edu/biology/professors/srenn/pages/teaching/...
General commemt: we can have increasing complexity, without a specific trend towards it, by positing evolution in all directions. We'd get mostly simple life, and fewer instances as complexity increases - which is what we do see. Most life is unicellular; there are more insect species than mammals etc.
I like that paper applying Moore's Law to biocomplexity, showing an exponential increase of the most complex life existing over time.
- It seems complexity increase is inevitable (but there could be barriers, as there seemed to be for dinosaurs).
- intelligence seems to increase with complexity.
Would mammals have expanded to today's diversity if the dinosaurs had survived? Would the ur-mammal instead have remained just one minor species or family, without those niches available?
And what caused the sudden increase in brain size of our own ape-like ancestors? (Surely, some killer application of intelligence, perhaps trade, that gave it incredible survival value, far above the value it already had).
So maybe dinosaurs are still working towards their limit. We know that their brains produce more pound per pound intelligence than mammalian brains. It's like they're more efficient.
But maybe something about that efficiency is Good Enough so they don't progress further.
Although watching my parrot at home is quite something. He's definitely on par with a young human in terms of coercing cooperation and puzzle solving.
Seeing galahs (Australian corvid https://wikipedia.org/wiki/Galah) socialize in trees in monkey troop-like fashion, dextrous in tooth and claw, makes me believe they are on the way. Though maybe raccons are next.
> efficiency is Good Enough
I was thinking that, now I think it may be the niche environment, which we somehow happened to stumble into, giving a more rewarding gradient for intelligence. OTOH, it could have been some neuroanatomy trick, eg faciliating abstraction/hypothesis. IDK. I think it's one of the more fascinating questions of our intelligence, and will be telling.
I don't want to harp on this point, but the birds-are-dinosaurs seems a meaningless semantic classification to me, more about our definitions than reality. Like "Pluto, planet?" I mean, why not call mammals a subgroup of reptiles, since we evolved from them? Anyway, I'm sure this debate has raged hotly across the centuries amoungst taxonomic philosophers, and carefully taking into account all the perspectives, they've collectively come up with... something.
It's a lot more direct than "mammals are a type of reptile".
Particularly because late stage dinosaurs, the theropods, had feathers and generally looked like birds with teeth that can't fly. Some later models could in fact fly.
If you look at this Wikipedia page: https://en.wikipedia.org/wiki/Feathered_dinosaur
You'll see that there is a single step from Velociraptor to Birds.
> The scientific consensus is that birds are a group of theropod dinosaurs that evolved during the Mesozoic Era. A close relationship between birds and dinosaurs was first proposed in the nineteenth century after the discovery of the primitive bird Archaeopteryx in Germany.
It took a lot of steps to go from reptiles to mammals.
What if we picked a domesticated animal such as a pig or dog, and began to breed the species for intelligence? Or any other suitable animal. Only intelligence (and general health), over an extended period.
It's believed that all of the modern dog breeds came about in the last hundred or so years. Modern domesticated dogs are definitely intelligent, especially socially intelligent. They understand words, they look you in the eye to get your attention, they understand their name, they seem to have simple emotions. How fast would they evolve if directed scientifically by humans?
... and at what point would we have to stop, because they're approaching human intelligence, making the program unethical?
The crazy thing about birds, parrots especially, is that they do all that without humans directing it.
I have a bird at home. The biggest difference I've noticed between having a bird and having a dog or a cat is that birds have moods. Dog/cat emotions always seem to directly correspond to what is happening right now.
Bird emotions seem to correspond to whatever has been happening for a while. Like, if you upset the bird in the morning, he acts towards you with resentment 12 hours later when you come home. It's hard to explain, but acting the same way towards my bird definitely produces different results based on his mood.
And he's very adept at getting attention and asking for help. For example, he's used to drinking water from human cups. If he's thirsty and there are no cups around, he's able to communicate that he needs me to go fetch a cup and fill it with water.
When he needs help with getting some food item, he's able to get my attention, then fly away to where he's having trouble, and signal that he needs help. He's even figured out, from observation, how to open some of the drawers in our apartment so that he can get treats.
Currently he's figuring out how to open cage doors. Luckily his main appendage is the beak so while he can open the cage physically, he can't hold the door open while he gets out. So it slams shut (by gravity) when he tries to walk through the opening. Fingers crossed he doesn't figure it out :D
It's really quite fascinating to observe.
Example: A bird may call your attention to a near-empty water dish. You fill it up. The bird uses bathing behavior to splash you with the water, and then mimics human laughter.
Source: a caique with whom I am acquainted.
But birds are also not very sophisticated as comedians. Sometimes their funny prank is indistinguishably similar to a nasty trick. But really, if the bird wanted to be mean, he'd just pretend to be chill, and then bite you in the webbing between your fingers. They do that sometimes, too.
It's one of the weirdest apocalyptic sci-fi novels around, in that it describes the end of the human race by isolation and loneliness and resulting escape into an alien world, while at the same time describing dogs creating a thriving replacement.
But they happen to be less destructive to their environment than humans so maybe that disqualifies them from the "dominate" part?
That said, humans also don't quality for multi-planetary. I like that definition, though.
True, but we've definitely sent probes to other planets, and a few people did manage to walk on the moon, so we're certainly farther to the right on the multi-planetary spectrum than any other species on our planet.
And yet, somehow Humans are in a completely different category than all other life. It's not just a matter a degree ("more" intelligent), it's a completely different category.
So that means your definition of intelligent is flawed because it is unable to capture that distinction. Perhaps you need a new word.
So we're not special enough anymore and we have to come up with a new word? I don't buy it.
It's likely that humans' extraordinary achievements stem from our immense ability to communicate and cooperate. A single human on its own isn't all that smart really.
Many intelligent animals suffer from limited knowledge transfer between generations and low cooperation between individuals. So each is only as smart as itself. Or maybe as itself and a couple of friends.
Whereas every human is able to tap into the intelligence of very many other humans. That's really one of our biggest superpowers.
Whenever I see this written I like to point out that the "we" in this case was only a vocal minority of people throughout history.
Anyone who's ever lived or worked with animals, at the very least mammals and birds, would have observed them being intelligent.
I'm sure this idea that people used to think animals weren't intelligent is a myth in the same way we think people used to believe the Earth is flat is a myth[1].
> Be civil. Don't say things you wouldn't say in a face-to-face conversation. Avoid gratuitous negativity.
Agriculture, written language, metal smelting, universities, space shuttles, nuclear bombs, radio, computers, etc.
It was obvious to me that we're in a whole other category from other species. But then I thought about human tribes in the rain forest that don't have any of those. Are they not as intelligent us? But they are us... Hm, well you've made me think. Thanks!
Look at the recent discoveries in the Amazon basin. Layers of dirt thousands of years old, still filled with the charcoal used to improve soil quality. Species of plants that were clearly selected for over time. The list goes on.
Lol no we are not. We share 98 percent of our DNA with various simians. We share 97 percent of our DNA with mice.
Are we the only species to communicate? No. Are we the only species to communicate symbolically? No. Great Apes use hand gestures.
Are we the only species to recognize themselves? No. Plenty of animals do. In fact, even wasps can perform facial recognition on members of their species.
Are we the only species to use technology? No. Corvids and apes use tools all the time.
Are we the only species to develop culture? No. Simians teach their young various customs, some of which (such as the washing of food by macaques in Japan [http://alfre.dk/monkeys-washing-potatoes/]) are local to the group.
Are we the smartest species? Monkeys have been able to naturally memorize a sequence of numbers after looking at it for fractions of a second. It took dedicated teams of research scientists several practice sessions to even come close to the performance of a so-called "lesser animal".
Humans are exceptional (I honestly would just say lucky), but are we truly in a different category? Highly recommend the book "Are We Smart Enough To Know How Smart Animals Are?" by Frans de Waal.
The difference is in degree, not of kind.
Everything is a difference of degree. At a certain point, a difference of degree becomes a difference of kind. There is a difference of kind between a fungus altering its environment through enzymes it produces from its genetic programming and people inventing steam engines.
Or in more general terms, we have the ability to use our environment as a durable supplemental memory. This is what I would look for in assessing whether another species has the potential for human-like intelligence.
Painted or etched drawings on cave walls came long before writing, and no other existing species on Earth does that except if we teach them.
Non-homo species also do not domesticate fire. Fire means not being afraid of something that you usually have seen only in scary situations, and it can lead to writing tens of thousands of years down the road (papyrus happens to preserve well in a pyramid in the desert, but cooking clay tablets or melting metals works better everywhere else).
I feel pretty safe in saying fire had no direct influence on the development of writing anywhere. Chinese characters first show up carved into bones. (They are well-developed at this point; obviously they originated some other way. But we don't know how.) Cuneiform tablets were originally unbaked; baking for preservation was an innovation that happened long, long after writing was established.
And the difficulty of working with metal means it is totally unsuitable as a writing medium. Although particularly important cuneiform documents (peace treaties) were sometimes cast in metal, only the final draft would be -- as the treaty was "in negotiations", messages back and forth were in clay. A society that can only write on metal is a society that will never develop writing in the first place. There is no reason other than wishing to impart a ceremonial permanence to write in metal.
You mean like how some species of nut-hiding birds can hide over 20,000 nuts in distinct locations comprising several square miles of territory and then recall precisely where they are when necessary?
But imagine if the birds also carved symbols into tree trunks and taught their friends how to interpret the symbols to find hidden caches of nuts, or to share techniques for building more durable nests, etc.
Written language allows us to store, access, and share information beyond our individual memory limits. It is sort of a collective memory as well as an expansion of individual memory. I can write down the locations of 21,000 nuts, and I can hand that book off to you.
(I make no assumption as to why we have Turing machines, but note that implementing one usually requires some work)
My point isn't that humans aren't amazing, it's that we perhaps think too highly of ourselves in relation to our incredible relatives.
There is nothing to translate, basically.
We can get a good grip of the meaning of their sounds though, if we spend some time listening, but there is no deeper meaning hidden that we can not access.
See, species tit-for-tat is easy. What's your point?
It's plausible any life that evolved there would be restricted to that continent. Humans evolved in warm climates and could adapt to cold climates by building shelters and wearing clothing. An animal that evolved in a cold climate would have a much harder time colonizing warm climates.
And since then glaciers have scraped the surface clean and there would be little remains of them.
<ridiculous_conspiracy_theory> I read another, much more crazy, theory, that the government is covering up something in Antarctica. There are so many untapped resources in Antarctica. And after WWII, lots of were exploring it and trying to lay claim to them. Then suddenly everyone left and a treaty was signed banning mining there. To protect the most desolate continent on Earth from... environmental harm? In the 1950's when environmentalism was such a big thing? And there are a suspicious number of military bases down there... And they are guarding what, exactly? What did they find... </ridiculous_conspiracy_theory>
I find stories and myths around Antarctica fascinating. It's one of the last places on Earth humans haven't turned every rock.
Mining wasn't banned until 1991. And as the article outlines, Antarctica is a really, really inhospitable place, to the point that it might be easier to colonize a different planet than to colonize Antarctica (I'd probably prefer equatorial Mars over Antarctica) and even mineral extraction would be very complicated.
Antarctica has the extremely important benefit of having earth gravity, whereas Mars is 1/3 the gravity of Earth.
Your health would rapidly decline on mars - everything from your bones becoming brittle to your muscle mass wasting to your teeth decaying. Your body would just fall apart.
I think this proves that there was no civilization advanced enough to travel between continents for however many millions of years the evolutionary isolation can be proven. I'm guessing it's at least some dozen Megayears.
And anything we've stuck on the moon.
Not to mention, all of the LACK of things. Giant holes from mining operations. All the straight cuts we've made through mountains. The Panama Canal.
Stone tools have been found that are 2-3 million years old - https://en.wikipedia.org/wiki/Stone_tool
The pyramids are already approaching 5,000 years old. Do they show any signs of disappearing?
Water, on the other hand, will tear through your stones much more quickly. In a wet, temperate climate, the weak acid falling from the sky will wear limestone. The moisture invading cracks and freezing will widen those cracks. Lichens will bore tiny holes into the rock, and plant roots will cause fissures to expand. Additionally, moisture that penetrates to metallic structural reinforcement will oxidize and swell that reinforcement to pop bits off of the stone (observable from earlier attempts at restoration at the Parthenon, where the replacement anchor pins weren't coated in lead correctly, and they started to crack the rock blocks--now they use non-corroding titanium pins). Sometimes mortar does not swell or expand at the same rate as whatever it binds, and something will crack, admit water, and generally deteriorate from there.
Water is the enemy of preservation. They pyramids didn't survive just because they are stone, but because they are also dry.
And on a long enough geological timescale, every potential building site will eventually experience every climate, including being entirely immersed in salt water.
This was the first I've heard that assertion, so it sent me down a bit of a rabbit hole.
Turns out it's a common story that Napoleon used the Sphinx for target practice, hence the lost nose. It also turns out that that is most certainly not true. Napoleon, being wholeheartedly in favor of the enlightenment, would never have destroyed antiquities (only plundered them for his own profit -- lets not forget that the Rosetta Stone was discovered during a Napoleonic campaign).
Further, a 15th century Arab historian notes that the nose was missing in his era and "attributes the loss of the nose to iconoclasm by Muhammad Sa'im al-Dahr—a Sufi Muslim from the khanqah of Sa'id al-Su'ada—in AD 1378, upon finding the local peasants making offerings to the Sphinx in the hope of increasing their harvest. Enraged, he destroyed the nose, and was later hanged for vandalism."[0]
0) https://en.wikipedia.org/wiki/Great_Sphinx_of_Giza#Missing_n...
P.S. thanks for sending me down that rabbit hole - I haven't idly done some armchair egyptology since I was a teenager
Earth is already well on the backside of how much longer it will be hospitable to life. First life was ~4 billion years ago. First multicellular life, 1.5. And now here we are, the first intelligence of our kind, clearly closely related to the animals we descended from, but just as clearly different in how our minds work.
That's one example in 4 billion years, and the Earth has between 500 million to 1 billion years left before the ever-increasing brightness of the sun boils the oceans and sterilizes the planet.
It could easily be that life is stunningly common across the universe, but that 80% is at the level of bacteria, and 99.x% is simple animals at best.
To give you an idea of the timescales involved, at the very birth of the solar system, right after the Earth coalesced, solar output was approximately 70% of what it is today.
It's not quite as bad as it sounds- if there is technological, intelligent life on Earth a billion years from now, simple diffraction gratings at the Sun::Earth L1 point could stretch the remaining time for hundreds of millions of years. Not something we can currently achieve, but it is within the realm of possibility. Beyond that is pure speculation.
EDIT: fossil record -> geological record.
There are actually a number of probes at the Sun-Earth and Earth-Moon L2 points already [1], because it's a perfect spot for telescopes and observatories. I don't know if any of them are big enough to easily observe from Earth, though.
[1]: https://en.wikipedia.org/wiki/List_of_objects_at_Lagrangian_...
(*it will rather quickly wander from its original position, but it isn't leaving orbit or crashing down.)
65M years is a long time and I have no idea what, besides radiation and meteorites, would cause something to decay on the moon. Is it possible for something the size and rough composition of a car to survive?
My personal nerd theory along those lines is there there may have been life on Earth before the giant impact that created the moon. All evidence of any sort of life whatsoever would have been buried under hundreds of miles of magma. It's very unlikely, as the Earth was so young at that point that it might not even have had a solid crust yet, but I find it compelling. :)
I wrote a little about it http://stochastication.com/2016/06/13/inverse-archaeology/
Scrimshaw seems like it would be pretty good evidence of intelligence.
The first evidence of multicellularity is from cyanobacteria-like organisms that lived 3–3.5 billion years ago.[5] https://en.m.wikipedia.org/wiki/Multicellular_organism
Now this is a Biofilms ala mats of multi celled organisms so it's hard to draw a clear line based on the fossils. Other contenders are much younger, but even if you use sexual reproduction as the benchmark that's still within the first 3 billion years and earth likely has another 1.75 billion to 3.25 billion years before it gets to hot.
https://en.wikipedia.org/wiki/Allan_Hills_84001
and
https://en.wikipedia.org/wiki/Microbially_induced_sedimentar...
And, of course, that's not evidence that there's still life on Mars.
[1] https://en.wikipedia.org/wiki/Spontaneous_generation [2] https://en.wikipedia.org/wiki/Anthropic_principle
A couple days ago I submitted a link to the Great Filter article on Wikipedia https://news.ycombinator.com/item?id=14095912
It basically proposes a theory where life, being very common in the universe, eventually reaches a point (filter) that prevents it from stepping up in the Kardashov scale: http://28oa9i1t08037ue3m1l0i861.wpengine.netdna-cdn.com/wp-c...
You are simply putting ourselves beyond the Great Filter, although finding life in Enceladus could drastically affect that: http://28oa9i1t08037ue3m1l0i861.wpengine.netdna-cdn.com/wp-c...
More info on this topic: https://news.ycombinator.com/item?id=14113461
I'd be more or less inclined to believe that once you have the first microbes advanced enough to support cell2cell signaling, and some kind of "condensed blueprint information mechanism" (what DNA is on Earth), the rest of the ring would pretty much be unavoidable, though slow.
Human-level intelligence might be rarer, in that you'd probably need a quite few evolutions to plateau + extinction cycles (think cambrian extinction, dinosaurs' extinction and probably a few others), most likely more than we had on Earth (I's assume we kind of got lucky), probably since what you get to something like "monkey level intelligence", most increases in intelligence would be disadvantageous for survival, unless they happen in a species with a tool-usage-friendly body plan + some pack/social tendency + environment change to challenge them to evolve but not to extinct + "construction friendly solid-ish environment" (I imagine dolphins, squids and octopuses, and most monkeys plateaued because they lacked at least one ingredient of the magic combination, and this tends to be the rule...), but this should pretty much happen.
And then you have the fact that our galaxy should have a few billions or tens of billions of Earth like planets based on what we know (probably more "life friendly" planets if you allow that other chemistries than "carbon + liquid water" could support life), it's pretty much unavoidable that there are quite a few human level species in the gallaxy.
The scary bit it that there should be quite a few above that, that probably went past their first singularity/transcendence event and are no longer constrained by biology and individual mortality and probably dumped their biological bodies long ago... scary being the fact that we don't see any sign of their presence.
There are a quite a few creatures sitting at the boundary between unicellular and multicellular like colonial algae (https://en.wikipedia.org/wiki/Volvox) and hydra (https://en.wikipedia.org/wiki/Hydra_(genus) - I call this one "at the boundary" because you cans simply cut a piece of an adult and have the pieces heal intro 2 live adults, so "being multicellular" happened before having proper genomic mechanisms for encoding body plan and body plan related cell differentiation for this organism, for example, information pattern is all emergent based on relative position of cells - there are experiments to prove this, it's not all inference from what I said above). So there's no missing link here, you can have a pretty smooth continuum from unicellular to "proper multicellular" (like body plan with cell types differentiation encoded in genome so it can "boot up" from just one fertilized cell). Also yeasts and unicellular algae have pretty huge genomes with tons of redundancy / duplication / room to spare / room to accommodate multiple cloned copies etc..
Yeah, biologists do like to point out that there are "very clear differences" between the organisms I mentioned above, and that they are clearly separate things, because they do love their beloved classifications of things :) (god forbid one puts an organism on wrong shelf of their library)... but if you look at things more computationally/informationally, there's a lot of flexibility and no clear gaps/boundaries "down at the bottom of the tree of life"... really can't see anything that evolution would have a problem searching through, no big ridges to block gradient descent in this problem space (like there are before proper-unicellular-life-with-genetic code, despite all "RNA world" theories... that's why I'd be more inclined to think that there may be planets with life supporting condition where microbial life has not had the chance to start yet despite the requirements being there... rather than life "getting stuck" at the microbial stage)
So certainly there's no missing link there. Heck, you've even got prokaryotes forming bacterial mats. The clear boundary is, again, between small cells that resperate over their surfaces and more complex cells that can resperate using structures throughout their interiors.
In that case you must not ignore the corollary: If there is no life on those moons, then it must follow that life is ridiculously rare.
And in that case, then it's pretty likely we are indeed alone in the universe.
1:https://www.quora.com/What-is-the-biomass-of-bacteria-What-i...