[charles-salvia]

Based on the developments in exo-planet research along with discoveries like this over the past couple of years, I would conjecture that life is ridiculously common. But by life, I mean microbial life. I would imagine that multi-cellular life is much rarer, and life capable of reaching human-level intelligence and beyond is probably absurdly rare, on the level of something like one species per galaxy. It's all worthless conjecture, of course, but the point is I wouldn't be surprised if microbial life is very, very common.

[nostrademons]

I'm kinda curious if there's any evidence that would support or rule out intelligent life having existed on earth before.

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.

[jerf]

I've thought about this and my conclusion is that we will likely leave behind a very strange pattern of certain natural resources. "Oh, look, here's a vein of copper! It's getting better, and better, and, that's weird, it's gone now and there's a complete break in the strata for some reason." Over time new mountains may form some new deposits, but it may be noticeable in the older mountains (that are today the younger mountains) for a long time.

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.

[ageofwant]

If there were any high-intelligence species before they must have exited in a time predating current coal and oil formation, or were not technologically capable, or found some other way of harvesting energy. The fact that we found massive amounts of planet-killing coal and immediately started exploiting it with abandon means that that did not happen before, ergo no technologically capable species on this planet for at last 300M years back. Now you could argue that 'intelligent species' tend not to shit in their own beds. We talk about Fermi filters for a reason.

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.

[nojvek]

I absolutely believe that any intelligent species that has enough intelligence to become interstellar will heavily invest in camouflage and become a lurker. Only reacting when something threatens its survival. The universe is like a jungle full of scary things, the only wise move is to watch out, be invisible and not make a lot of noise.

[aleksei]

I get your point, but I posit that this is a very human point of view. Once you've cracked the energy needs for interstellar travel, what's the point of raising a war campaign light years away (especially if you need generation ships to attack)? Furthermore, it doesn't seem very intelligent to me that all capable species just hunker down in their own gravity well to die off unnoticed and without having explored the universe. Humans have thus far always endeavoured to go one step beyond; why stop now?

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.

[vidarh]

They wouldn't need generation ships. You "just" need sufficient tech to put engines on a suitable astroid and accelerate it to a decent fraction of c; it only needs enough logic to fine tune the path. An invasion force is horribly inefficient vs. just slamming a lot of mass at someone at high enough speed.

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.

[pchristensen]

If this is interesting to you, read The Dark Forest: https://www.goodreads.com/book/show/23168817-the-dark-forest...

[nojvek]

Thanks for the recommendation

[colkassad]

This is an interesting theory. Perhaps you could expand on it and form a new social science called "Cosmic Sociology".

[dmichulke]

Aren't Twitter, FB and selfies a sign of the opposite happening at the micro level?

[vidarh]

Despite the occasional swatting, for the most part the consequence of being spotted on social networks is not to have the local lunatic show up to shoot you in the face.

That's a rather significant difference to the proposed idea.

[builditand]

He was talking about intelligent species.

[sundvor]

Good thing we're keeping so quiet then... :P /s

[bonzini]

1000000 years ago, homo erectus was bashing rocks. You cannot really know what Bonobo chimps are going to evolve into so far in the future.

[nostrademons]

Curious if anyone's ever observed something similar to this? It'd be super easy to detect if you're looking for it, but most miners aren't thinking "Hmm, I wonder if a previous intelligent species existed on earth millions of years before us."

[azernik]

Mining companies generally hire very smart geologists who care a lot about the processes that shape resource deposits, in order to predict where new deposits will be found. If there were any pattern that didn't fit with natural processes people would notice

[TheSpiceIsLife]

Surely if a previous society extracted megatons of ore from the ground there would be something left of that civilisation. At least a wheel track or a scrape mark, not to mention maybe a spanner.

[ioddly]

Pretty sure evidence of Roman metallurgy can be detected in the ice record.

http://science.sciencemag.org/content/265/5180/1841

[pavel_lishin]

I started thinking that another species after us would find it odd that there are so few hydrocarbon deposits - but would they look for something that's not there?

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.

[aaronblohowiak]

The fungus (white rot) that breaks down an important binder in woody plants (lignin) had not yet evolved when the plants that make up our coal and gas deposits died. because white rot now exists, we aren't making new coal or oil at anywhere near the same rate.

https://www.scientificamerican.com/article/mushroom-evolutio...

[SmellTheGlove]

If we cause a mass extinction, including that of ourselves, wouldn't we be creating a lot of hydrocarbon deposits eventually?

(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?)

[pavel_lishin]

My understanding is that most of them came from plant life, and a lot of that from the ocean - so I don't think the animal biomass would really add that much.

[V-2]

That's assuming intelligent life always builds an industrial civilization...

[Ralfp]

How else could they cope with growing needs for goods or, say, entertaiment as their civilization develops?

Or would you then argue that intelligent life could develop sort of moratorium on further development in line with their value system?

[cmdrfred]

Or they fail to thrive like humans have. Early humans were few in number and might have nearly died out a few times. We just got lucky.

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.

[zebrafish]

I don't think you're allowed to pose the dolphin question. If we assume that dolphins and humans have a common ancestor and that the dolphin branch ever had a need for using tools to sustain their species, over time enough random permutations of specific genes would have selected those dolphins which had appendages capable of aiding in the use of tools. As it turns out, they did not need to have hand like appendages to survive and thus apes have hands and ocean mammals do not.

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.

[JumpCrisscross]

> All our buildings would've...been crushed by plate tectonics

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.

[1] https://en.m.wikipedia.org/wiki/Continental_crust

[2] https://en.m.wikipedia.org/wiki/Oceanic_crust

[technotony]

Well geologists think our impact can already be measured enough to leave a trace and are calling the era of man the 'Anthropocene'. Climate change and mass extinction are two of these features, but there will also be radiation from nuclear tests, plastic waste and impact of domestication on animal fossils. https://www.theguardian.com/environment/2016/aug/29/declare-...

[ddinh]

What about space artifacts? Out in the vacuum stuff corrodes/degrades much slower - would satellites still be around or would they have had their orbits degraded and burned up in the atmosphere? Also, how detectable would the stuff we've left behind on Moon (the mirror, perhaps? Only thing that can probably destroy evidence of our presence on the moon would be asteroid impacts) be to a civilization that doesn't know it's there?

[nostrademons]

Most satellite orbits should decay and burn up in the atmosphere long before a few million years has passed. Most of the near-earth orbits become unstable within decades, and the ones that don't are subject to gravitational perturbations from the moon and other planets.

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.

[c517402]

There are corner reflector arrays on the moon that might make someone curious, if millions of years of moon dust doesn't effect them or they aren't destroyed by an asteroid impact.

[scythe]

Mines seem like a possibility. Hmm, this kind of rock is usually associated with these minerals, but not when these weird streaks appear.

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.

[caf]

Presumably we could look for ¹²⁹I in deep Antarctic ice cores?

[Swizec]

> I'm kinda curious if there's any evidence that would support or rule out intelligent life having existed on earth before.

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/...

[hyperpallium]

I thought corvids a strong candidate, but if they've been around for 25 million years without getting human-level intelligence, they mightn't ever get it, like the dinosaurs.

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).

[Swizec]

Well, birds are dinosaurs. Avian theropods to be precise.

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.

[hyperpallium]

Spiders also produce more pound per pound intelligence. They are solitary. What if they became social? Brain-body ratio is provocative, but not the whole story.

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.

[Swizec]

> 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.

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.

[Pyxl101]

Here's a crazy idea:

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?

[rojobuffalo]

We're sharing the planet with several intelligent species at this moment. Maybe a worthwhile distinction would be intelligence sufficient to dominant an entire planetary ecology; or sufficient to intentionally become multi-planetary.

[Swizec]

Dominate the planet is tricky too. Corvids for instance are almost as widespread as humans. They don't do greenland and the southern parts of south america.

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.

[rojobuffalo]

Good point about corvids. Ants are another example I was thinking about. They actually do engineer ecology on the scale of individual mounds by feeding and growing fungi that they eat. They are spread all over the Earth, and I think they have us beat in terms of biomass. Maybe there could be another definition for a weaker form of intelligence that covers those cases.

[SAI_Peregrinus]

Ants are especially interesting. Each individual is very simple, you could probably create an accurate ant model with a (very big) finite state machine. Yet entire colonies are extremely complex. I suspect that it's analogous to human brain cells vs the entire brain. Each cell isn't intelligent alone, but the whole is.

[eric_h]

> That said, humans also don't quality for multi-planetary.

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.

[ars]

> It's hard to say which species was first to become intelligent, but I'm pretty sure humans weren't the first.

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.

[Swizec]

How do you know it's a completely different category? We used to think all animals are incapable of intelligence and everything they do is "instinct". Now we know they can think, organize, have complex social structures, even imagine and form plans. Many show evidence of being self aware.

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.

[TheSpiceIsLife]

We used to think all animals are incapable of intelligence and everything they do is "instinct".

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].

1. https://en.wikipedia.org/wiki/Myth_of_the_flat_Earth

[adrianN]

Animals not being intelligent is also very convenient if the bible teaches that they're made for our use. There are fewer ethical problems if they're soulless automatons without consciousness or intelligent.

[losvedir]

Heh, I originally started this comment "oh come on!" as I thought you were being needlessly obtuse.

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!

[Baeocystin]

Human tribes in the rainforest have levels of social sophistication, technology, and manipulation of their local environment that outstrips any other animal. It's not close.

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.

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

[milquetoastaf]

>And yet, somehow Humans are in a completely different category than all other life.

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.

[ams6110]

Biology notwithstanding, no other species has deliberately transformed its environment and improved it longevity and standard of living like humans have. Not even slightly.

[milquetoastaf]

Animals transform their environments all the time, deliberately (I don't get why people act as if animals don't do deliberate things?). What of the great honey fungus in the Blue Mountains of Oregon, a living organism whose size is measured in miles - it deliberately transformed its environment in a way we, the species Aristotle put at the top, can barely even comprehend.

The difference is in degree, not of kind.

[hyperpallium]

You can argue for their intelligence, but they can't argue for yours.

[milquetoastaf]

Is argumentation and rhetoric the basis of intelligence?

[JetSetWilly]

We share 50% of our DNA with a banana. That doesn't mean that a banana has all these incredible human characteristics. Stats about "percentage of DNA shared" are meaningless. A very small change in DNA can produce very large changes in the organism - ones fundamental to its nature.

[milquetoastaf]

It's the fact that we share the DNA with such diverse amounts of life that matters. You argue that humankind is fundamentally different and exceptional than all other life is to reinforce the hierarchy set forth by Aristotle and offers an outdated pyramidal view of the biosphere. The more we share, the more in common we seem to have. You can't tell me it's meaningless, that's just completely ignoring decades of scientific research.

[scythe]

My answer to this is simple: we have Turing machines. Somehow, our communications are Turing-complete, whereas other species's aren't.

(I make no assumption as to why we have Turing machines, but note that implementing one usually requires some work)

[milquetoastaf]

Your answer is as simple as it is unsatisfactory and arbitrary. Humans have turing machines, sure. But we have yet to truly translate an animal language (though we do know they exist) so your point is rather moot.

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.

[zeroer]

Recursive grammar.

[milquetoastaf]

Being able to live six years without food. Humans can't even come close to that, yet a tiny tick can outlast the so-called smartest species on earth.

See, species tit-for-tat is easy. What's your point?

[danmaz74]

See sorites paradox.

[Houshalter]

I've read an interesting theory about this before but I can't remember the source. If there was intelligent life on Antarctica, it would be impossible for us to detect it today. Antarctica was warmer once and could have supported much more life.

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>

[Flow]

Have you seen the subbreddit for "Antarctic Anomalies"? https://www.reddit.com/r/AntarcticAnomalies/

I find stories and myths around Antarctica fascinating. It's one of the last places on Earth humans haven't turned every rock.

[BurningFrog]

That, and the bottom of the ocean!

[winfred]

Here you go: http://www.coolantarctica.com/Antarctica%20fact%20file/scien...

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.

[api]

I read a great rundown once on /r/space about how Antarctica actually is in many ways less hospitable than Mars, at least in winter. I find that rather amazing.

[awirth]

Perhaps you're thinking of this thread? https://www.reddit.com/r/space/comments/2xvdow/why_worry_abo...

[rsync]

"(I'd probably prefer equatorial Mars over Antarctica)"

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.

[bonzini]

At least if you get to Antartica you don't need a pressurized suit and an airlock to go outside. It's difficult to imagine a less hospitable world than one without an atmosphere and a magnetic field (well, not talking about Venus-level inhospitable).

[Houshalter]

Also the biggest barrier to colonization is transportation. It's much easier to get to Antarctica than it is to Mars. Lots of humans have been to Antarctica. It's unlikely anyone will ever set foot on Mars for the foreseeable future.

[krylon]

H.P. Lovecraft's "At the Mountains of Madness" comes to mind... ;-)

[herbstein]

Isaac Arthur has a very interesting video that touches on that specific topic, but with a space exploration angle.

https://www.youtube.com/watch?v=k7fLNvpl0c8

[nikolasavic]

I love his channel! I'm surprised it isn't more popular, it has top notch content and regularly scheduled releases.

[Ataraxy]

My favorite youtube channel out in the wild! His videos are such a treat every week.

[leonroy]

That was incredibly good. Some of the ethical and practical implications raised in that video by humans actually achieving interstellar travel were pretty eye opening.

[BurningFrog]

One thing we can observe is that parts of the planet have been completely isolated from each other for many millions of years, until very recently when human travel has brought "invasive species" to places where they've never been.

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.

[kortex]

There are a lot of things which would likely not break down oven millions of years, provided they were largely protected from the element. A lot of glasses, ceramics. Tungsten carbide (pretty much any super hard machine tool, as long as it wasn't subducted). The isotopic distribution of nuclear waste would be a big clue.

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.

[sharun]

Stone degrades faster than bone?

Stone tools have been found that are 2-3 million years old - https://en.wikipedia.org/wiki/Stone_tool

[spydum]

always wondered how exactly this process works.. you can date the stone itself, but how do you date the shaping of the stone?

[stevenwoo]

The assumption is the surrounding sediment can suffice for a good enough approximation. http://www.nytimes.com/2011/09/13/science/13qna.html

[colordrops]

If we can find tons of fossils of animals and plants, I'm absolutely sure there would be fossils left behind of cars, houses, etc

[GlennS]

Largest stone monuments gone after 10,000 years? Are you sure?

The pyramids are already approaching 5,000 years old. Do they show any signs of disappearing?

[mihaifm]

If you only take erosion into account, they are likely to last millions of years. If someone takes them apart piece by piece...that's a different story.

[JuliusKaiser]

No, because they are maintained for tourist and historical value.

[usefulcat]

But said maintenance is relatively recent (~100 years?) compared to their age.

[adrianN]

I'd guess that the Egyptians maintained them. If I'm not mistaken they where in pretty good shape during Roman times.

[logfromblammo]

Human activity weathers stone monuments faster than desert winds. If I recall correctly, the original sheathing stones and capstones of the pyramids were gradually stolen. The Sphinx was used for target practice.

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.

[824ueirwfjd]

actually they do... also human intervention ensures they'll be around longer most likely

[Cyph0n]

How do we know that 65 million years is long enough for a species with a human-like intelligence to evolve? What if our evolution was merely a biological fluke that took much less time than usual?

[pacman128]

A common misconception about evolution is that follows a linear progression to higher forms. There is no ladder it's ascending, it's a spreading tree ( http://evolution.berkeley.edu/evolibrary/article/evo_07). It's a system that is exploring a fitness landscape with many local maxima for reproductive success. We have no prove that developing a species with self-aware intelligence is inevitable.

[Baeocystin]

I think this is a particularly salient point.

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.

[swombat]

My understanding from Astrophysics class back at uni was that sun-like stars spent 5-10b years on the main sequence, so I thought we may well have another 5b years of quality sunshine to enjoy. Or not.

[Baeocystin]

You're right, in terms of the sun's ultimate lifespan. Unfortunately for us, the Goldilocks Zone is very sensitive. To achieve full solar sterilization of the Earth only requires ~10% greater output from the sun, for example. And that will happen long before the sun leaves the main sequence.

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.

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

[kahoon]

Certainly possible. Dinosaurs were around longer than mammals and their intelligence did not reach human-level. Makes sense if we consider that evolution is a blind process which does not "aim" for creating higher intelligence, and may only happen by chance if it suits the given environment better than other traits.

[zeroer]

I'm still waiting for intelligent life.

[nerfhammer]

Some of the skeletons will be wearing gold jewelry.

[throwaway91111]

It would still be visible in the fossil record, IMHO. Stone can still form around structures that long faded away, and there is zero evidence of any tool before our recent relatives (apes).

EDIT: fossil record -> geological record.

[S4M]

How about the things we would have left in extreme environments: Internet cables at the bottom of the sea, rubbish (or dead people with clothes) high in the mountains, or remnants of polar expeditions in the South pole?

[scythe]

Antarctica will eventually leave the South Pole if I understand it correctly.

[flubert]

I wonder about satellites. How far above the earth's surface would a satellite have to be to keep atmospheric drag low enough to keep an artificial satellite in orbit for a long long time. And how big would it need to be for it to be naked eye visible at that distance. And what could be done to make it unlikely to be mistaken for a natural phenomena? Have clusters of satellites in geometric patterns? 65 Million years is a long time. That sounds like a more interesting project than the "Long Now" effort.

[crooked-v]

For something to last a really long time, you'd want to have it at one of the Lagrangian points. Have it be big and reflective - say, a tremendous expanse of reflective cloth behind a relatively small probe - and anybody with a telescope and patience will eventually spot it as a weird "star". Something shiny at a Lagrangian point will suggest something weird (compared to the non-shinyness of objects collected at the Lagrangian points of other planets), making it an obvious target for investigation by space probes.

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_...

[alphydan]

Not any Lagrangian point will do. L1, L2, L3 are unstable so a small perturbation will send your satellite away. Only L4, L5 will do under certain conditions for the mass of the satellite [0]

[0] https://map.gsfc.nasa.gov/ContentMedia/lagrange.pdf

[Baeocystin]

Anything in geosync is there* until the sun boils the oceans.

(*it will rather quickly wander from its original position, but it isn't leaving orbit or crashing down.)

[SmellTheGlove]

You might be able to find some of our shit still in orbit. Also, I'm not sure of the timescale for things to decay on the moon, but would something from Apollo be left up there? Depending on how far into the future, what if something bigger eventually got built?

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?

[kobeya]

Fossilized bone survives 65Myr, but granite buildings and metal tools do not leave even the slightest fingerprints? I'll call BS.

[pchristensen]

If this comment is interesting to you, you may enjoy the book The World Without Us. https://www.goodreads.com/book/show/248787.The_World_Without...

[PhasmaFelis]

I think strip mines wouldn't be too difficult to detect. Some of them are comparable in size to the ancient craters we've discovered. Maybe canals--I don't think there'd be much left, but maybe enough to notice an unnaturally straight depression running for hundreds of miles. I wonder if aqueducts and transport tunnels could survive the ages, in hard rock in a geologically inactive area; but I suppose the entrances would probably be buried in any case.

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. :)

[njwi332]

Don't forget radioactive waste/byproducts. That will be around for a long time, and thinking about how future humans might interact with it is an interesting problem.

I wrote a little about it http://stochastication.com/2016/06/13/inverse-archaeology/

[thaumasiotes]

> You'll find occasional fossilized skeletons, but all that would tell future species is that a bipedal mammal with a large brain once existed.

Scrimshaw seems like it would be pretty good evidence of intelligence.

[Retric]

On earth the jump from single celled life to multi celled life was very rapid relative to how long planets can probably support life on average.

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.

[guelo]

That is bad conjecture. We have no evidence of life anywhere besides earth, microbial or otherwise. Exoplanet research and this new data has found planets that could conceivably host life, but that's it.

[Symmetry]

Well, we do have evidence of past life on Mars - just not conclusive evidence. See

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.

[Grue3]

Why would life be ridiculously common? It cannot appear by itself, that would be "spontaneous generation" [1], a long rejected theory. The Earth is extremely suitable for life. It could've easily supported independently evolved life-forms. Yet every living thing we know has a common ancestor, including extinct organisms. Just based on that fact, the odds are firmly stacked against other life anywhere near us. The fact that we can observe life on Earth is just a consequence of Anthropic principle [2] and says nothing about the probability of life emerging on other planets.

[1] https://en.wikipedia.org/wiki/Spontaneous_generation [2] https://en.wikipedia.org/wiki/Anthropic_principle

[rnet85]

Spontaneous generation was never a valid scientific theory. For a more accurate one look at https://en.wikipedia.org/wiki/Abiogenesis Also, the probablity of generation of organic compounds which are precursors to life is pretty high given right environment, https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment

[fauria]

I don't think it's a worthless conjecture.

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

[nnq]

What intuition makes you believe that once you have microbial live + some kind of stability (low levels of ionizing radiation + a decent level of chemical stability, so not too hot), evolution to advanced multicellular organisms is not pretty much the default?

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.

[Symmetry]

The problem is that basic microbes only resperate over their surfaces so they have big square/cubed law limits on how large they can be and, by extension, on how complex their genomes can be. You need a hopeful monster that can run its metabolism throughout the cell to develop large genomes of the type that can support differentiated cells in multi-cellular creatures.

[nnq]

> You need a hopeful monster that can run its metabolism throughout the cell to develop large genomes of the type that can support differentiated cells in multi-cellular creatures

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)

[Symmetry]

I'm not talking about the difference between unicellular and multicellular life. I'm talking about the difference between small cells that resperate over their cell walls (prokaryotes and archaea) and cells that resperatory organelles (eukaryotes). Both algae and hydra are already over this barrier and I agree that once you're a eukaryote or the alien equivalent there's an easy path from there to complex multi-cellular interactions.

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.

[cJ0th]

On a related note, there has been an interesting episode of BBC's CrowdScience. They reported that robots which go to Mars (to find out about microbial life) have to go through an extreme cleaning process to make sure that they contaminate Mars as little as possible with microbial life from our planet .

http://www.bbc.co.uk/programmes/p04nmxzl

[ars]

> Based on the developments in exo-planet research along with discoveries like this over the past couple of years, I would conjecture that life is ridiculously common.

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.

[andrewflnr]

(Life on enceladus -> Life is common) does not entail (No life on enceladus -> Life is rare) by any length of proof, much less one short enough to let you call it a "corollary" with a straight face. This would be so even if "Life is common" and "Life is rare" were perfect logical complements, rather than being endpoints on a wide spectrum.

[moomin]

I'd guess that microbial life would evolve into cellular life almost anywhere there was enough heat.

[blacksmith_tb]

Multicellular? Most organisms on earth are unicellular[1] even now. My impression is that multicellular organisms evolved because the 'easy' evolutionary niches were already occupied by single-celled species, and it took new tricks to compete for new niches.

1:https://www.quora.com/What-is-the-biomass-of-bacteria-What-i...

[theparanoid]

It's not known exactly how multicellular life came to be. It's happened only once in the history of the earth. Nuclear dna is from Archaea and Mitochondrial dna is from bateria. Lynn Margulis was the first to propose and substantiate symbiogenesis for this.

[Symmetry]

You need more than heat for life to evolve. You also need a source of useful energy. Probably a long-lasting chemical gradient like you see in undersea vents but there are a number of possibilities. Life has evolved on Earth to use other sources of energy too, most commonly sunlight, but the machinery to use those is much more complex.

[otempomores]

I think addhoc multicellular life could be very comon too

[komali2]

I dunno man, the galaxy alone is pretty darn big.