Fermi Paradox

[PB666]

On August 6, 2016 at 8:57 PM, magnemoe said:

Civilization would be hard to detect, either we are lucky to listen to an random radio signal or spot an laser or we detect something blocking their star or other obvious effect then looking trough an good telescope. 
Life as in an oxygen atmosphere is far simpler to detect however it only tells us that they have an oxygen atmosphere however this question will likely be answered later this century:
How common is planets suited for life and how many of them have life 

An manned starship is way out of our experience, even interstellar probes or colonization in our solar system is far ahead.  interstellar colonization would be hard even for someone far more advanced than us, more so as it looks like its an decent distance between habitable planets, not 4 lightyear in average but more like 20-40. 
Most alien civilizations either don't take the cost who would be significant even for an scale 1 civilization. 

Now if we found an easy stardrive the first question would be where are the aliens? 

Travel is very difficult, but if it can be done, over millions of years it would be done. So lets say the universe was ripe with life 100 million years ago and it takes a million years to branch, from one civilization there are 2^100 civilization, this means there are 10^31 colonized from one single, we would see them.

So either interstellar travel isn't possible, or its really really really hard. Or space faring civilizations were not possible or very very rare 100 million years ago. 

[magnemoe]

13 minutes ago, PB666 said:

Travel is very difficult, but if it can be done, over millions of years it would be done. So lets say the universe was ripe with life 100 million years ago and it takes a million years to branch, from one civilization there are 2^100 civilization, this means there are 10^31 colonized from one single, we would see them.

So either interstellar travel isn't possible, or its really really really hard. Or space faring civilizations were not possible or very very rare 100 million years ago. 

This assumes that someone start with star traveling and don't stop, also that many of their colonies continues to do this over an timespann of million of years.
Currently it looks like it would be expensive even for an scale 1 civilization, one who have access to as much energy earth get from the sun. 
Lot of it depend on the average distance between habitable planets.


 

[PB666]

2 hours ago, magnemoe said:

This assumes that someone start with star traveling and don't stop, also that many of their colonies continues to do this over an timespann of million of years.
Currently it looks like it would be expensive even for an scale 1 civilization, one who have access to as much energy earth get from the sun. 
Lot of it depend on the average distance between habitable planets.


 

Allright lets say interstellar travel is possible. All of human technology occurs within 100,000 years, but a space faring civilization would have a huge jump start. So lets say 10,000 years maximum to get from entry to go somewhere else.

Second Earth could send a ship to Centuari-Proxima but also 10 or so other worlds (say all 10 stars within 10 light years), maximally it would take 10,000 years to get to each. So that means we quintruple number of worlds in say 10,000 years once we reach say 100,000 years from now. So that means doubling time is once every 30,000 years. In 100,000,000 we easily have occupied every single star that can be bridged by say 100 ly travel in the entire galaxy, though I am sure some stars would not be reached because of hazards.

Not only this, but our solar system would have been colonized many time by different routes here from that same single starting system and it would be currently occupied by a number of colony ships floating around in the sun.

So either we are really clueless about sentient life in our system, they are very stealthy, interstellar travel is really really hard or impossible, or we are the first in an evolution that will populate the galaxy. If that is the case we may never see life in other galaxies because the space-time frame only allows us to look backwards in intergalactic time.

Lets talk about risks.

Could we be the first life form in the universe to define the universe (something beyond the scope of the visible universe that contains all energy and matter). Not impossible as one sentient had to have been first, but in comoving space-time, the question becomes meaningless.

Could we be the first life form in the galaxy to reach this level of sentiency. Improbable, but not impossible. The premise is that our galaxy evolved from gas and has been progressing with the evolution of more complex matter (more heavier elements), in the progression there are points were life is impossible, then becomes very rare, then more common place, then tolerant of sentient life, then probable that sentient life will appear. A half-life for first sentient life. During that progression one life has to be the first sentient and we could be that life form. Space-time is also tolerant of multiple first, this is because "age" is a measure of the progression of time and is dependent on speed and proximity to the galactic center where things age less quickly.

So now, we have an 100,000 year interstellar ship, it reaches destination and it collects comets and asteroids, and builds colonies (easily less than 1000 years for each colony) after accumulating a certain number of 1000 colony ships each with its own specialized factories it then begins build the next interstellar travel ship, no need to landing on habitable planets, but habitable planets would be terriformed and colonized at convenience. For example planets around red stars that have finally exited the flare stage might have material from the oort belt brought in to make atmosphere, filtering the elements to add just th right amount of oxygen and hydrogen and nitrogen, then adding the right seeds (like cyanobacterium and other organisms to slowly build up life. Once you have 'bread crumb' colonies between Earth and 'terriform' planet you could transfer complex ecosystem inhabitants by cryogenic storage (egg or spores) that are then implanted into mechanized 'maternobots' that specifically provide the needs for each organism and bring species back to life on the new world. The sentients could build specialized command and control, invention centers etc on these worlds.

[tater]

A perhaps more likely scenario is AI. Any possibly spacefaring (in the interstellar sense) society will come up with AI before interstellar ships (or about the same time). I'd bet we have some form of AI before even a "star shot" was possible to be completed if it were a major focus (which it isn't).

This makes sending probes that much easier, which does bring about the "where are they" paradox. Clearly the answer must be that intelligence up to this point is very rare, or that decent probes are really hard to do, or that such a probe has already zipped through our system, but they are flyby probes already coasting by the time they are here, and we'd never notice them.

 

[magnemoe]

6 hours ago, tater said:

A perhaps more likely scenario is AI. Any possibly spacefaring (in the interstellar sense) society will come up with AI before interstellar ships (or about the same time). I'd bet we have some form of AI before even a "star shot" was possible to be completed if it were a major focus (which it isn't).

This makes sending probes that much easier, which does bring about the "where are they" paradox. Clearly the answer must be that intelligence up to this point is very rare, or that decent probes are really hard to do, or that such a probe has already zipped through our system, but they are flyby probes already coasting by the time they are here, and we'd never notice them.

 

Probes are way easier it will however only do recon in the system, an von neumann probe does not however will be pretty hard to make, probably easier than an colony ship, you can take more risks and don't need an ecosystem. 
Still even von neumann probes will not do much more than move out and report back that they find, yes you would probably want them on standby afterwards, if you want to send an colony ship they could build the infrastructure something who would be very required anyway unless the target planet was very nice. 

Even for an pure AI civilization going interstellar has limited interest, you might want to colonize multiple stars as an safety to preserve your species, the other drives is glory, science and exploring. This will be less interesting as you move out.
Its plenty of resources in an solar system and moving out will not reduce your population or resource problems in any way unless you have very easy FTL.If you have population or resource problems you would be too poor to go interstellar anyway. 

Planets with advanced life is probably pretty rare, say 20-40 light year between, intelligent life looks pretty rare then looking at earth history, yes current mammals and birds are pretty smart so you might get another intelligent species however this might take 50 million years. Now humans are a bit special in another way, we works very well in large groups, in an way we are closer to social insects than other smart mammals here, this is random and not something who could evolve nor had time for it but it would be no civilizations without it, yes we would still spread out over all of earth, been apex predator and even start farming but no states just villages. 
Lots of other filters, an intelligent predator would have far lower population density worse if its no domesticatable animals.
Aliens might get into traps we avoided, not smart enough so you are not able to come up with solutions to problems who hit you, like using coal then you start running out of wood, this problem grows acute then you industrialize, you need new solutions all the time. 
Easy communication and nuclear weapons could very easy give an world government, good chance it would end up as imperial china freezing stuff and it don't help how smart you are. 
More not able to restrict their population, note that in most  industrialized countries humans are below reproduction rate who is another issue. 
Anyway the matrix looks more fun than the outside world. 
 

[Green Baron]

RNA world hypothesis gets a little backup:

http://www.sciencemag.org/news/2016/08/newly-made-rna-strand-bolsters-ideas-about-how-life-earth-began

 

[Diche Bach]

On 6/1/2016 at 7:20 PM, gpisic said:

@PB666 

You can't seriously believe that there is no life out there? Even if it happens that we are the only sentient beings in the Milky Way did you even think about how many more galaxies are out there ? There will probably never be a way to detect any signals from them but that for sure doesn't mean that there is no life out there,

What about the "galactic habitable zone" stuff?

Quote

Subsequent studies saw more fundamental revision of the old concept of the galactic habitable zone as an annulus. In 2008, a study by

Nikos Prantzos revealed that, while the probability of a planet escaping sterilization by supernova was highest at a distance of about 10 kpc from the galactic center, the sheer density of stars in the inner galaxy meant that the highest number of habitable planets could be found there.^[3] The research was corroborated in a 2011 paper by Michael Gowanlock, who calculated the frequency of supernova-surviving planets as a function of their distance from the galactic center, their height above the galactic plane, and their age, ultimately discovering that about 0.3% of stars in the galaxy could today support complex life, or 1.2% if one does not consider the tidal locking of red dwarf planets as precluding the development of complex life

As an evolutionary scientist, I think the fact that life exists AT ALL seems fairly miraculous (although once it gets going it seems that nothing can "stop it" from diversifying into virtually anything and everything the environment allows), and the "Rare Earth Hypothesis" seems cogent enough. The list of possible "random occurrences" that have been proposed as preconditions to make Earth able to support the early evolution of life is long.

Even if there are 700 billion "stars" in the Milky Way, if immediately ~98% of those are eliminated as "candidate evolutionary cradles" because of Galactic Habitable Zone issues, and then the issues of "Rare Earth" factors are accounted for . . . the actual percentage chance that any given celestial object in any given solar system in any given galaxy (much less the Milk Way) might be so close to zero that literally the sparking of the first replicating amino acid strands on Earth was a miracle.

In sum, from my standpoint: we do not know, and the chance that Earth is THE ONLY object with life on it in the universe, seems to be just about as tenable as the chance that there are others out there.

ADDIT: I will be delighted beyond all imagining if science manages to produce more and better tangible evidence of the possibility of the evolution of extraterrestrial life (infinitely more-so if that proof is actually suggestive OF THE EXISTENCE of extraterrestrial life).

I am disappointed, that a mere ~100 year lifespan is simply not enough to know how the story unfolds in the long-term. I figure in 10,000 to 100,000 years we should have a decent sample size and better empirical generalizations on which to rest our models . . . perhaps even a true foundation on which to rest a fledgling "Exobiology" discipline. If at all possible, I do hope to either watch proceedings from the "Afterlife" else to come back to check it all out again, because like @ Aethon I find this stuff to be the most fascinating of all questions.

However, in the mean time, I remain skeptical of the existence of life anywhere except that which we can observe closely, i.e., that on Earth, and make no presumptions one way or the other about its probability of existence elsewhere in our solar system, or in the universe as a whole.

Not suggesting everyone must remain that undecided, but I think that it is a worth considering as the "most gratifying" mindset: Wonder is after all, the state of not knowing more or less, and this is pretty much mutually exclusive with dogma.

Edited August 18, 2016 by Diche Bach
artistic license

[Green Baron]

I see it the same way, once the evolution get's going it can only be successfull in a sense that it brings forward organisms that are fit for the given circumstances ....

... with a limitation: IF there are stable conditions over a long time (4.5 billion years in our case).

In common words: only earth managed to keep the temperature in the necessary boundaries, it offers sinks and valves for greenhouse and icehouse elements, a strong magnetic field as a radiation/particle shield, a moon for stabilisation of the axis, an ocean, plate tectonics for stabilistation of climate over very long periods. Jupiter keeps unwanted guests away. Our sun is a quiet star and earth could compensate for the change in radiation and heat output, there is no interference from other celestial bodies like multi-star-system. The galactic neighborhood was quiet.

Evolution would not have been successfull (and of course still is successfull despite of human interference sorry couldn't resist :-)) on earth had conditions been more "spacey". Extinction events never touched all layers / niches, there were allways enough survivors (species) that evolution could continue with variations in the blueprints.

 

Personal belief: I wouldn't go that far to say "unique in the universe", such apodictic words aren't very "sciencey", or are they :-) ? But similar condtions just around the corner are *very* unlikely.

 

Edit: The search for planets can only measure guesstimate "distance from the sun" and "size", and even these with great uncertainties. Calling a distant planet a "second earth" is of less information value than calling mars or venus a second earth. They are not.

2nd Edit: it's too early to say "first steps to replicating RNA-strands are a total miracle". It's not totally clear how these first steps looked like but i'm sure the problem will be solved one day. And we're not running out of ideas yet and we surely don't need "wonders", science might suffice ;-)

http://www.nature.com/nature/journal/v459/n7244/pdf/nature08013.pdf

http://www.nature.com/nchem/journal/v7/n4/full/nchem.2202.html

http://www.sciencemag.org/news/2015/03/researchers-may-have-solved-origin-life-conundrum

 

Edited August 18, 2016 by Green Baron
fit

[magnemoe]

On 18.8.2016 at 5:02 PM, Diche Bach said:

What about the "galactic habitable zone" stuff?

As an evolutionary scientist, I think the fact that life exists AT ALL seems fairly miraculous (although once it gets going it seems that nothing can "stop it" from diversifying into virtually anything and everything the environment allows), and the "Rare Earth Hypothesis" seems cogent enough. The list of possible "random occurrences" that have been proposed as preconditions to make Earth able to support the early evolution of life is long.

Even if there are 700 billion "stars" in the Milky Way, if immediately ~98% of those are eliminated as "candidate evolutionary cradles" because of Galactic Habitable Zone issues, and then the issues of "Rare Earth" factors are accounted for . . . the actual percentage chance that any given celestial object in any given solar system in any given galaxy (much less the Milk Way) might be so close to zero that literally the sparking of the first replicating amino acid strands on Earth was a miracle.

In sum, from my standpoint: we do not know, and the chance that Earth is THE ONLY object with life on it in the universe, seems to be just about as tenable as the chance that there are others out there.

ADDIT: I will be delighted beyond all imagining if science manages to produce more and better tangible evidence of the possibility of the evolution of extraterrestrial life (infinitely more-so if that proof is actually suggestive OF THE EXISTENCE of extraterrestrial life).

I am disappointed, that a mere ~100 year lifespan is simply not enough to know how the story unfolds in the long-term. I figure in 10,000 to 100,000 years we should have a decent sample size and better empirical generalizations on which to rest our models . . . perhaps even a true foundation on which to rest a fledgling "Exobiology" discipline. If at all possible, I do hope to either watch proceedings from the "Afterlife" else to come back to check it all out again, because like @ Aethon I find this stuff to be the most fascinating of all questions.

However, in the mean time, I remain skeptical of the existence of life anywhere except that which we can observe closely, i.e., that on Earth, and make no presumptions one way or the other about its probability of existence elsewhere in our solar system, or in the universe as a whole.

Not suggesting everyone must remain that undecided, but I think that it is a worth considering as the "most gratifying" mindset: Wonder is after all, the state of not knowing more or less, and this is pretty much mutually exclusive with dogma.

Your timespan is off by two magnitudes for the amount of life. Just by checking the atmosphere on the promising planets found by kepler and follow up missions we would get good data for the chance of photosynthetic life, if common it would also tell who planet types supporting it and who not, if we don't find any we know life is very rare. 

Checking for life on Europa and other ice moons would also be interesting and also something who will probably happen the next 100 years.
Not so useful for answering the chance of life in the universe unless the life is totally unrelated to earth life. 
It might also be that ice moon oceans lack the condition for creation of life even if life could survive there. 

Yes, you can get oxygen from other sources but oxygen will react with the ground and volcano will bring new materials who will bind with oxygen. It took over an billion year from start of photosynthesis to significant oxygen levels on earth. An waterworld where water if splitt into hydrogen and oxygen by sunlight and the hydrogen escapes will give oxygen too but should be possible to filter out. 

An more advanced telescope than webb with an sunshade would be able to take pictures of planets with enough details to show continents, it would also show their colors and if life is common on land. Continental plant growth would be an strong indicator of more advanced life than microbes. 

Don't we will get more data without sending probes to the planet but the telescope data will answer the first two questions. 

[Diche Bach]

On 8/20/2016 at 5:06 AM, magnemoe said:

Your timespan is off by two magnitudes for the amount of life. Just by checking the atmosphere on the promising planets found by kepler and follow up missions we would get good data for the chance of photosynthetic life, if common it would also tell who planet types supporting it and who not, if we don't find any we know life is very rare. 

Checking for life on Europa and other ice moons would also be interesting and also something who will probably happen the next 100 years.
Not so useful for answering the chance of life in the universe unless the life is totally unrelated to earth life. 
It might also be that ice moon oceans lack the condition for creation of life even if life could survive there. 

Yes, you can get oxygen from other sources but oxygen will react with the ground and volcano will bring new materials who will bind with oxygen. It took over an billion year from start of photosynthesis to significant oxygen levels on earth. An waterworld where water if splitt into hydrogen and oxygen by sunlight and the hydrogen escapes will give oxygen too but should be possible to filter out. 

An more advanced telescope than webb with an sunshade would be able to take pictures of planets with enough details to show continents, it would also show their colors and if life is common on land. Continental plant growth would be an strong indicator of more advanced life than microbes. 

Don't we will get more data without sending probes to the planet but the telescope data will answer the first two questions. 

I'm not sure you've read the stuff on "Rare Earth." What do you mean by this part "Your timespan is off by two magnitudes for the amount of life"?

I'm a bit skeptical that a telescope will ever be able to provide compelling evidence of the existence of life on a extrasolar body, but that is just pure skepticism. I realize there are promising avenues for overcoming the glare of the star, and many "signals" that could be looked for. But I have my doubts that any of those signals, or even all of them combined provide a 95% valid indicator of "life."

The other question, about which I am far less knowledgeable (20 years of training in biological anthropology doesn't help so much with understanding black holes! ) and which probably deserves its own thread--but which is in some sense an analog of the "Not-Fermi's Non-Paradox": Are Black holes the "wombs" of daughter universes!?

[Green Baron]

I think i have already outed myself as a "rare earther", but only with respect to earth itself, nobody can say much about other planets. I hope we can answer the question whether microbiotical life could emerge elsewhere when we can bring samples from the other icy/whet/formerly whet bodies of the solar system to earth and/or send a very well equipped expedition out there. But really, i don't see that in the next 25 years, too many questions are still open. Before that happens i rather see that the question of what happened on earth between 0 and 1 o'clock will be answered and maybe the chemistry replicated.

As for telescopes: interferometry , combination of small telescopes to form a larger one. Has been done for longer wavelengths (radio) and the latest telescopes are constructed with that in mind, ALMA and VLA probably the best examples. Thus huge stars have been imaged as discs (beteigeuze) and a protoplanetary disc 450ly away. But a lot of data must be shoveled around. If one could combine telescopes on opposite sides of the earth or between earth and the lagrange-points or even the earths orbit (2 au !) that'll be a fine and sharp view of the vicinity. Dreams of the future but not total fantasy ...

 

Edited August 21, 2016 by Green Baron

[magnemoe]

2 hours ago, Diche Bach said:

I'm not sure you've read the stuff on "Rare Earth." What do you mean by this part "Your timespan is off by two magnitudes for the amount of life"?

I'm a bit skeptical that a telescope will ever be able to provide compelling evidence of the existence of life on a extrasolar body, but that is just pure skepticism. I realize there are promising avenues for overcoming the glare of the star, and many "signals" that could be looked for. But I have my doubts that any of those signals, or even all of them combined provide a 95% valid indicator of "life."

The other question, about which I am far less knowledgeable (20 years of training in biological anthropology doesn't help so much with understanding black holes! ) and which probably deserves its own thread--but which is in some sense an analog of the "Not-Fermi's Non-Paradox": Are Black holes the "wombs" of daughter universes!?

My point is that future telescopes perhaps webb or at least follow up ones will be able to do atmospheric spectroscopy of exoplanets.
As posted above O2 is not an sure sign of life however, the other options would either give traces or not an remotely earth-like atmosphere +2 bar of oxygen would not be stable. Neither would an bone dry planet have life. 
So this will give lots of data, if we look at the 50 most earth like planets and find that they all have atmospheres somwhat between Mars and Venus we know life is rare. 
If not next up in getting images like we have of Pluto from earth of exoplanets, this will show continents and also hint plant growth. on land. 
This is in the 50 to 100 year timeline not 1000-10000 years. 
Note that if we don't find good atmospheres funding of an planetary mapper telescope will take longer, 

 

[magnemoe]

1 hour ago, Green Baron said:

I think i have already outed myself as a "rare earther", but only with respect to earth itself, nobody can say much about other planets. I hope we can answer the question whether microbiotical life could emerge elsewhere when we can bring samples from the other icy/whet/formerly whet bodies of the solar system to earth and/or send a very well equipped expedition out there. But really, i don't see that in the next 25 years, too many questions are still open. Before that happens i rather see that the question of what happened on earth between 0 and 1 o'clock will be answered and maybe the chemistry replicated.

As for telescopes: interferometry , combination of small telescopes to form a larger one. Has been done for longer wavelengths (radio) and the latest telescopes are constructed with that in mind, ALMA and VLA probably the best examples. Thus huge stars have been imaged as discs (beteigeuze) and a protoplanetary disc 450ly away. But a lot of data must be shoveled around. If one could combine telescopes on opposite sides of the earth or between earth and the lagrange-points or even the earths orbit (2 au !) that'll be a fine and sharp view of the vicinity. Dreams of the future but not total fantasy ...

In space its 3rd way, you don't need an uniform circular mirror who cover all unless you are after maximum brightness in the smallest possible package.
Make an telescope with 2-4 arms, not much more mirror areal than web but say 100 meter wide, you now have an 100 meter optical telescope. 
http://www.nextbigfuture.com/2016/08/a-proposed-space-telescope-for-quality.html

Unfolding the arms would also not be much more complex than webb, yes the sunshade will be harder, note that with the cost of webb,developing an larger fairing and doing an test launch of an falcon heavy will not affect the budget much. 
You will probably also want an free flying sunshade for this. 
Purpose is to find continents and plant growth on them, it should give decent indications of at least multicellular life.
An advanced long baseline interferometry telescope or something using sun as an gravitational lens would give more date as you say. 

[KAL 9000]

After reading this thread, I'd like to submit my own opinion:

Habitable planets are probably common-ish. Life is probably rare. Getting the conditions in a warm little pond or hydrothermal vent for a form of self-replicating RNA or something to form is HARD. I would estimate sentient life at probably one planet per galaxy. So, yeah, we'll find some rare amoebas or something, but we're probably the only life that has discovered space travel in the Milky Way.

Of course, this is all thrown off if panspermia happened, which is a question for another thread .

[PB666]

http://www.dailygalaxy.com/my_weblog/2016/08/worlds-astronomers-warn-our-21st-century-technology-is-too-primitive-to-detect-a-hostile-advanced-ci.html

[magnemoe]

3 hours ago, KAL 9000 said:

After reading this thread, I'd like to submit my own opinion:

Habitable planets are probably common-ish. Life is probably rare. Getting the conditions in a warm little pond or hydrothermal vent for a form of self-replicating RNA or something to form is HARD. I would estimate sentient life at probably one planet per galaxy. So, yeah, we'll find some rare amoebas or something, but we're probably the only life that has discovered space travel in the Milky Way.

Of course, this is all thrown off if panspermia happened, which is a question for another thread .

This is something who is impossible to prove or disprove in an lab. We don't know the chance for life starting, we even don't know how it started, we only have some theories. 
Say its an 50%  chance of life starts on an planet in x*100 million years. on earth life started pretty early so x will be between 1 and 3, this might the the standard or if we was very lucky and x is more like 1000, we don't know as if we was not lucky we would not had this discussion, 
An lab work on too short timescale and too low volume to have any chance to discover this.

Again good telescopes will give us decent data here. 

Personally I think life and even advanced live is pretty common, however planets who can support  life is rarer than we hoped. 
Intelligence is rare, technical civilizations are very rare and almost all of them find the matrix more fun. 
 

[KAL 9000]

2 hours ago, magnemoe said:

This is something who is impossible to prove or disprove in an lab. We don't know the chance for life starting, we even don't know how it started, we only have some theories. 
Say its an 50%  chance of life starts on an planet in x*100 million years. on earth life started pretty early so x will be between 1 and 3, this might the the standard or if we was very lucky and x is more like 1000, we don't know as if we was not lucky we would not had this discussion, 
An lab work on too short timescale and too low volume to have any chance to discover this.

Again good telescopes will give us decent data here. 

Personally I think life and even advanced live is pretty common, however planets who can support  life is rarer than we hoped. 
Intelligence is rare, technical civilizations are very rare and almost all of them find the matrix more fun. 
 

All very good points!

[Diche Bach]

Age of Universe: 13.79 billion years old

Age of Milky Way Galaxy: 13.6 billion years old

Age of Sol: 4.6 billion years old

Age of Earth: 4.5 billion years old

Age of Life: earliest undisputed 3.5 billion years old, speculated to have occurred 3.8 to 3.9 billion years ago

Also from link above:

Earliest water on Earth: ~4.4 billion years ago.

Earliest oxygen: 3.5 billion years ago

Earliest atmospheric oxygen: 2.5 billion years ago

Earliest Eukaryotes (critters with membrane-bound organelles, seemingly a precondition for multi-cellular much less "complex" life): 1.6 to 2.1 billion years ago

Cambrian explosion: 0.54 billion years ago

So in sum, despite the Milky Way being nearly as old as the universe itself, our entire solar system was just a cloud of dust until the Milky Way was two-thirds of its current age. One could say "our solar system didn't even form until our galaxy was already 'elderly'" but I think that wouldn't be quite right, as the "death" of the Milky Way as a result of its merging with Andromeda is not in the cards for another 3.75 billion years or so, and even then, it will not "kill" the Milky Way so much as "blend it" it my understanding . . . the end result being en elliptical merger galaxy of the two.

Apparently, this collision of galaxies may have little real impact on the solar system, but by then it will be irrelevant to life on Earth because Sol will have already bloated into a Red Giant and evaporated all the liquid water, thus ending life on Earth . . . I would think that by then, we "humans" will be living inside nanoparticles and have colonized not only anything remotely colonizable in the Milky Way, but quite possibly the Multiverse(s). Once we master the technology to make our physical bodies unnecessary, we might not even need planets, meh!

 . . . but getting back to life as we know it today . . .

So the Universe, and the Milky Way were already "old" in a relative sense, when the Sol system formed.

Water it seems was pretty quick to form on Earth, and that was seemingly the most critical element, supposedly only 100 million years or so after Earth formed . . . life however, took another 400 to 900 million years, and this was life in only the simplest sense: self-organizing and self-replicating organic compounds.

Are their planets with cyanobacteria-like critters out there? Certainly seems like a possibility. There may even be some other hosts to such life right here in our solar system. There are a lot of "rocks" to look under to find the little beasties though, so it might take a long, long, LONG time before we can say with certainty that there either IS or is NOT any life any where else in our solar system. Literally, until virtually every comet, every asteroid, every moon, every planet where some exotic form of primitive life might have clung to existence would need to be looked at closely, very closely, and thoroughly, and there ain't a telescope one can dream of that can replace people or our robots scraping the surface and looking at it under a microscope.

In this sense, the idea that "life might be abundant" or "common" or whatever, sure maybe. But (a) we are never going to detect this particular "fringe" and "clinging to existence" type of life until we (or our robots) actually start scouring the whole place. This is why I say 10,000 to 100,000 years. In that time frame, I reckon we'll have operations going all over the Sol system, and possibly in several adjoining systems as well, and by then billions of tons of rock and ice and gas will have been processed, looked at, and/or analyzed and thus, IF there are any stray microbes living anywhere besides Earth that time frame seems about long enough for our species to extend its "touch" to a significant enough section of our galactic neighborhood that we must might stumble on it. If microbial life turns out to be fairly common, then it might come much earlier. But that seems unlikely at this stage: still no signs of anything on Mars as far as I know and certainly nothing from any of the other bodies we have some scrappings from so far.

And then we have "life" in the sense of what most people think of: at least multi-cellular, if not photosynthetic = produces oxygen and progressively reshapes the right type of planets so that they can eventually host the sorts of life we think of as characterizing Earth (though in truth the bacteria are the real "rulers" of the planet, still to this day . . . ). Bodies that have experienced these types of processes might well stick out like a sore thumb, just detecting oxygen in an exoplanets atmophere would be pretty telling as far as I understand it. But so we find a planet that is "roughly" Earth like in every other respect (inferred gravity, goldilocks zone, etc.) AND we discover it has an appreciable Oxygen content in its atmosphere, then what? Given the closest possible one is what? 50 light years away? Its not like it is going to make a damn bit of difference to humanity, though it is of course fascinating and I encourage them in their studies all the way.

But again, we come back to my 10,000 to 100,000 number . . . by then, MAYBE we will have the propulsion technology to make a journey of 50 light years tenable in something less than the time it has taken humanity to go from Homo erectus to modern humans?

I played around with some numbers several years ago, and (just from memory) best I could figure, closest star system to ours, Alpha Centauri, which is what 2.6 light years? no, 4.37 light years . . . at the best speeds we can currently achieve (leaving aside things that are theoretically possible but have yet to be proven like Orion nuclear pulse stuff . . .) that is like a 45,000 year journey!

Don't get me wrong, I find the whole exoplanet revolution to be absolutely stunning and wondrous. But the fact is, without better propulsion, all the remote analysis evidence in the world is going to remain "below the 95%" threshold and is likely to do so for many thousands of years, i.e., until we have the capacity to put machines and/or people ON those distant bodies and scrape the surface with a probe.

[Green Baron]

7 hours ago, Diche Bach said:

 

Just a few remarks/nitpicking, for completion: the cambrian explosion thing was probably an artifact and has overcome itself since the discovery of the ediacaran. "Explosions" or "Revolutions" in earth history or archeology (example: Vere Gordon Childe's "neolithic revolution") are very often artifacts, revolutions may even have a political taste from those who invent them :-). Anyway, things need their time to develop.

The cloud out of which the solar system formed contained a lot of metals (anything else than H and He), since these are bread in stars and supernovae other stars must have formed before, exploded in supernovae, formed a protoplanetary disc, out of which solar systems evolved and so on. If these stars were larger than the sun than these processes were much faster. But the cloud wasn't just there waiting to condensate, it was other star(s) before.

Andromeda / Milkyway will probably form a huge elliptical galaxy "afterwards", the mixing up is no cataclysmic thing, it's rather like two gases mixing. Others have been through that before :-) But Andromeda will be a fine sight in the far future (if there is someone to watch).

The ocean (different chemistry than today) formed immediately after the crust solidified. Probably evaporated several times because of impacts / volcanism and rained out again. I see the first microbes a little older (not much) than you describe, formed before 4 billion years. The rest is browsing through the archives :-)

But as you say, in order to tell whether microbes formed on other bodies in the solar system it would not suffice to turn a stone and there they are. We'd have to understand how the dynamics of these bodies work to be able to find the places were the beasties might have been / are. Imagine somebody 4.1 billion years ago, landing on earth in a quiet moment, looking for life. Would he(kirk)/she(janeway) have the idea to go to the bottom of the ocean and look around volcanic vents ? It might already be elsewhere as well, but they would probably not find it if they didn't have expectations were to look and what to look for.

Earth is exceptionally complicated, nevertheless finding life(tm) means much more than sending a probe (if we don't step accidentally on it or if it somehow says "We're here !"). It might take 100 or 10.000 years ... since i'm more into the past than the future i can't tell. 10.000 is a long time and we might have beaten each other up struggling for resources, like we did so many times before ... or become victims of evolution because some nasty microbes are fitter ... hehe.

 

Edited August 23, 2016 by Green Baron

[Diche Bach]

I think I know what you mean about that "artifact" concept. Another example, which I believe is reversing now somewhat: for the longest time, the oldest and "best" and richest archaeological record of modern humans was in Europe, not in Africa where the critters were supposed to have "arisen" first. Seems like that is an artifact of a history of archaeology in which more people did more archaeological field work in Europe and North America (and to a lesser extent Asia and South America) than in Africa. This also dovetails with the point I made about "finding the microbes:" Science finds stuff where and when scientists look someplace, and the fact that that stuff is there and "not" in places where scientists have not looked much yet doesn't mean it is only in the place where it is known to be.

Still, would you seriously consider that the "Cambrian explosion" might not actually have been a dramatic event from the standpoint of rapid adaptive radiation? The past is so mysterious, nearly as much so as the future, it boggles the mind that, out of the millions, perhaps even hundreds of millions of "species" (another concept that is arguably "artifactual" to some extent, much as is the concept of "gene," etc.) 99% of them are now extinct and many left no living descendants!?! As least that is one of the few things I let Stephen Jay Gould convince me of in an off-hand way . . .

The ocean forming: most of my geology course work dealt with either Earth history at the grand scale, or surficial earth processes (cave formation) else the Quaternary, so the formal coursework I've had that dealt with this stuff was about 30 minutes of lecture and perhaps 3 pages in one or two text books . . . Not to mention the fact that, after 30 years, there may well have been some "revolutions" in thinking in the Earth sciences . . . surprisingly there seems to have been a major discovery that Earth's past climates were always pure, chaste and pleasing until nasty industrialists starting belching forth carbon in the past few years, which really throws a monkey-wrench into the fundamental points of my whole training, i.e., that Earth's climate has more or less ALWAYS fluctuated, and more erratically at some times (particularly the last 2.5 million years . . . but I digress . . .) . . . isn't it thought that the "water" got brought here by bolides?

As far as the "oldest" microbes, etc.,: again not my area of expertise, and even if it had been, a mere 3 year departure from the latest literature can lead to effectively 95% ignorance, so I satisfice myself with whatever claims manage to become "consensus" on Wiki at this stage.

I view scientific thought sort of like a bell-curve: on the far-left, the cutting edge, are new and "dangerous" ideas which are the stuff of frantic scribblings and late-night cappuccino binges by their respective stewards into human consciousness. This stuff only tends to get passing mention, if any mention at all in sources like Wiki, and oft times the wiki history will reveal an ongoing struggle of the grad students and geek-groupies who are supporters/posers/wanabes of the respective rival conceptual factions . . . If the author of one of these "wild ideas" manages to get tenure and continue to gain traction/reputation/fame/patents over a few years or decades by constructing evidentiary support for the idea (meaning no one else can see how to tear down their sand castle) then it will eventually become "prevailing wisdom" and merge into the center of the bell-curve and wind up as "front page" news on Wiki, and at which point, we might consider it to be "what science thinks."

But then a few years pass, the original source of the idea is found to have made errors, or worse to have made stuff up, and the carcass of their work gets exhumed and dissected with glee. New ideas are formed, nomenclatures adjusted, terminology combobulated, 3-stage models replaced with 5-stage models, and everyone pats the "revisionist" on the back for having "fixed it" and at this stage, the idea that had originally been on the far left of the bell-curve, and lived comfortably in the middle for a good while, has now found the conveyor belt of science doesn't just shut off, and has slide over into the nether land of the "diminishing right-leg" of the curve. What is "correct" in no small degree depends on the time/date, not to mention which clique one seeks to identify with.

ADDIT: and then you get jewels like this one, where some drunken old European fart did some whacked out experiment, noted some weird excrements, it got archived (just because he was "generally a good guy" even though nobody had the least notion of what the hell his latest ranting even meant . . .) and then 200 years later, someone else found it in the "literature" and realized the predecessor had "discovered" something that "hadn't" been discovered yet!

Antonie van Leeuwenhoek liked to play with test tubes . . .

Quote

In his letter of 14 June 1680 to The Royal Society, Antonie van Leeuwenhoek described an experiment he carried out by filling two identical glass tubes about halfway with crushed pepper powder, to which some clean rain water was added. Van Leeuwenhoek sealed one of the glass tubes by using a flame and left the other glass tube open. Several days later, he discovered in the open glass tube ‘a great many very little animalcules, of divers sort having its own particular motion.’ Not expecting to see any life in the sealed glass tube, Van Leeuwenhoek saw to his surprise ‘a kind of living animalcules that were round and bigger than the biggest sort that I have said were in the other water.’ The conditions in the sealed tube had become quite anaerobic owing to consumption of oxygen by aerobic microorganisms.^[4]

In 1913 Martinus Beijerinck repeated Van Leeuwenhoek's experiment and identified Clostridium butyricum as a prominent anaerobic bacterium in the sealed pepper infusion tube liquid. Beijerinck commented:

'We thus come to the remarkable conclusion that, beyond doubt, Van Leeuwenhoek in his experiment with the fully closed tube had cultivated and seen genuine anaerobic bacteria, which would happen again only after 200 years, namely about 1862 by Pasteur. That Leeuwenhoek, one hundred years before the discovery of oxygen and the composition of air, was not aware of the meaning of his observations is understandable. But the fact that in the closed tube he observed an increased gas pressure caused by fermentative bacteria and in addition saw the bacteria, prove in any case that he not only was a good observer, but also was able to design an experiment from which a conclusion could be drawn.' ^[5]

Yeah! Antonie did have a fricking CLUE about oxygen but he sure could design a neat experiment!

 

Edited August 23, 2016 by Diche Bach
cryptic hyperlinkage

[Green Baron]

Since a few years i'm trying to renew my library on earth history, but each time i think "now i order" they announce new editions ... :-)

Humans: africa and europe/asia are different. Even the terminology/chronology is different. Africa hasn't gone through ice-ages. The ice-age in europe is more appealing and better researched on. Many people in the nineteenth century, especially in france and germany, looked for bones from "the tribe of the flat headed" (newspaper article on the find of the neandertal neandertal 1856 ... journalists ! :-)), it was a sport.

After the ice-age the neolithic(*) spread from the origin (the slopes of the mountains in southern turkey, syria, ...) towards the north, probably simply because environmental conditions allowed. Deserts to the south and east weren't that inviting. Surely some tried but weren't as successful as those who went north/west. So the "neolithic package" and subsequently copper, bronze, iron things didn't show up in africa first but were imported from outside. It's not only an artifact in this case, it's simply that there is more stuff to find in europe/asia than africa.

Modern culture / politics plays a role as well: muslims aren't interested in what was before mohammed (sorry guys) and not everyone is allowed to enter the countries and do research. That limits possible finds in arabia / western asia.

I can't say much about the americas, only that humans are assumed to have arrived there during the last glacial maximum. America doesn't play a role in the development of humankind (sorry guys and gals) :-)

Cambrian: well, depends, "pre-cambrian explosion" if you like ? Yes, the blueprints have changed since then. Ediacara-fauna were rather jellylike, soft animals. And yes, we can only see the prosperous models in the records, the hecatombs and majority of short-lived genusses are gone.

Climate: there have been ice-ages and greenhouse-times, even one or maybe two global icings, but on a large scale the earth always found back to these 15°C surface temp. Another one of these things why microbes mayhaps are not the big deal but the evolution over billions of years is.

Let's hope that Apophis or one of his colleagues doesn't change his mind and course to leave a lasting impression ....

 

(*) The relevant part for europe/western asia.

 

Edited August 23, 2016 by Green Baron

[magnemoe]

1 hour ago, Diche Bach said:

I think I know what you mean about that "artifact" concept. Another example, which I believe is reversing now somewhat: for the longest time, the oldest and "best" and richest archaeological record of modern humans was in Europe, not in Africa where the critters were supposed to have "arisen" first. Seems like that is an artifact of a history of archaeology in which more people did more archaeological field work in Europe and North America (and to a lesser extent Asia and South America) than in Africa. This also dovetails with the point I made about "finding the microbes:" Science finds stuff where and when scientists look someplace, and the fact that that stuff is there and "not" in places where scientists have not looked much yet doesn't mean it is only in the place where it is known to be.

Still, would you seriously consider that the "Cambrian explosion" might not actually have been a dramatic event from the standpoint of rapid adaptive radiation? The past is so mysterious, nearly as much so as the future, it boggles the mind that, out of the millions, perhaps even hundreds of millions of "species" (another concept that is arguably "artifactual" to some extent, much as is the concept of "gene," etc.) 99% of them are now extinct and many left no living descendants!?! As least that is one of the few things I let Stephen Jay Gould convince me of in an off-hand way . . .

The ocean forming: most of my geology course work dealt with either Earth history at the grand scale, or surficial earth processes (cave formation) else the Quaternary, so the formal coursework I've had that dealt with this stuff was about 30 minutes of lecture and perhaps 3 pages in one or two text books . . . Not to mention the fact that, after 30 years, there may well have been some "revolutions" in thinking in the Earth sciences . . . surprisingly there seems to have been a major discovery that Earth's past climates were always pure, chaste and pleasing until nasty industrialists starting belching forth carbon in the past few years, which really throws a monkey-wrench into the fundamental points of my whole training, i.e., that Earth's climate has more or less ALWAYS fluctuated, and more erratically at some times (particularly the last 2.5 million years . . . but I digress . . .) . . . isn't it thought that the "water" got brought here by bolides?

As far as the "oldest" microbes, etc.,: again not my area of expertise, and even if it had been, a mere 3 year departure from the latest literature can lead to effectively 95% ignorance, so I satisfice myself with whatever claims manage to become "consensus" on Wiki at this stage.

I view scientific thought sort of like a bell-curve: on the far-left, the cutting edge, are new and "dangerous" ideas which are the stuff of frantic scribblings and late-night cappuccino binges by their respective stewards into human consciousness. This stuff only tends to get passing mention, if any mention at all in sources like Wiki, and oft times the wiki history will reveal an ongoing struggle of the grad students and geek-groupies who are supporters/posers/wanabes of the respective rival conceptual factions . . . If the author of one of these "wild ideas" manages to get tenure and continue to gain traction/reputation/fame/patents over a few years or decades by constructing evidentiary support for the idea (meaning no one else can see how to tear down their sand castle) then it will eventually become "prevailing wisdom" and merge into the center of the bell-curve and wind up as "front page" news on Wiki, and at which point, we might consider it to be "what science thinks."

But then a few years pass, the original source of the idea is found to have made errors, or worse to have made stuff up, and the carcass of their work gets exhumed and dissected with glee. New ideas are formed, nomenclatures adjusted, terminology combobulated, 3-stage models replaced with 5-stage models, and everyone pats the "revisionist" on the back for having "fixed it" and at this stage, the idea that had originally been on the far left of the bell-curve, and lived comfortably in the middle for a good while, has now found the conveyor belt of science doesn't just shut off, and has slide over into the nether land of the "diminishing right-leg" of the curve. What is "correct" in no small degree depends on the time/date, not to mention which clique one seeks to identify with.

ADDIT: and then you get jewels like this one, where some drunken old European fart did some whacked out experiment, noted some weird excrements, it got archived (just because he was "generally a good guy" even though nobody had the least notion of what the hell his latest ranting even meant . . .) and then 200 years later, someone else found it in the "literature" and realized the predecessor had "discovered" something that "hadn't" been discovered yet!

Antonie van Leeuwenhoek liked to play with test tubes . . .

Yeah! Antonie did have a fricking CLUE about oxygen but he sure could design a neat experiment!

Yes archaeology and paleontology stared in Europe so they had an huge head start with discoveries. 
Its still slanted in that most people will dig there they know its something to find. 

As i understand the cambium explosion came after an snowball earth, then the ice melted it was an explosion of life who went in all sort of directions, I guess life had probably diverged a lot at the various hotpots where life survived so much of it is just an increase in biomass and fossils and it was only an revolution then looking back half an billion years. 
Afterward the competition got stronger and most of the experiments died out. 

Climatologists don't want to talk about climate later than 1850, doing so generate a lot of messy data and someone might even try to run the climate models on this data who would be even more of an mess. 

I disagree a bit about the bell curve, it depend a lot of how much is known, in sciences there we are pretty much in the dark or no definitive answers its a lot of shifting trends.
Else they mostly come from new discoveries who give focus, funding and a flood of theories. Later this calms down until something new changes it. 
Soft sciences tend to have more of the trends as its few fixed or definitive answers, its also often political loaded. 

Loved the closed test tube experiment, interesting as the water seal is standard then making beer or vine. i wonder then it was invented. 
 

[Green Baron]

42 minutes ago, magnemoe said:

As i understand the cambium explosion came after an snowball earth, then the ice melted it was an explosion of life who went in all sort of directions,

I love these dicussions but they take sooo much time :-)

The cryogenian glaciation is in discussion. Axial tilt, orbital "complications", these things ..... it might not have been global.

http://www.nature.com/ngeo/journal/v8/n9/full/ngeo2531.html

There was a total glaciation in the palaeoproterozoic. And before someone asks, i don't know how but am thankfull that the earth found out of that because a total glaciation tends to be a very stable state !

All in all glaciation were relatively short periods and are indeed connected to changes in life on the planet. As to Fermi: the air get's ever thinner for advanced extraterrestrial life .... :-)

 

Edited August 23, 2016 by Green Baron

[Diche Bach]

29 minutes ago, magnemoe said:

. . .  SNIP . . .
I disagree a bit about the bell curve, it depend a lot of how much is known, in sciences there we are pretty much in the dark or no definitive answers its a lot of shifting trends.
Else they mostly come from new discoveries who give focus, funding and a flood of theories. Later this calms down until something new changes it. 
Soft sciences tend to have more of the trends as its few fixed or definitive answers, its also often political loaded. 

Loved the closed test tube experiment, interesting as the water seal is standard then making beer or vine. i wonder then it was invented.

True about the social sciences being more squishy, but  . . . from my outsider perspective it looks like physics at least is showing signs of still not quite being "fully developed yet" too (not the Newtonian stuff, which seems "solid" at least in so far as it very nicely explains how stuff works at the "intermediate" scales): examples being A. traditional gravity only accounts for what? 25% of the observed "attraction" between stars and galaxies? thus the black box "we have no idea what this means" concept of "dark matter." B. The accelerating rate of expansion of the universe defies everything else and requires another deus ex machina in the form of "dark energy." C. and then we have that whole "quantum area" where even the most basic "experiments" with an LED and some cardboard with slits cut in it can reveal the true "boundaries" of scientific understanding.

We think we know a lot, but I suspect we know very damn little, and I think it behooves us to comprehend that. Moreover, some of the coolest "discoveries" happened a long time ago, and using the simplest of methods: for example that Greco-Egyptian fellow who inferred the diameter of the Earth to within 10% accuracy by measuring the shadows cast from poles placed and distant latitudes at the same time of day . . . can never remember his fricking name and thus impaired in finding links to discussions of his stuff. Want to say it was like "300 BC" . . .

 

[Green Baron]

1 minute ago, Diche Bach said:

that Greco-Egyptian fellow who inferred the diameter of the Earth

Eratostenes :-)