This reminds me of one of my favourite pieces of science writing ever: "Bands of Iron", by Adam Lee[0]. I don't think I've ever read something that better conveyed a sense of Deep Time[1] in the context of life on this planet:
> Unlike today, there were no oxygen-breathing animals to expire carbon dioxide and close the cycle, and so it quickly built up in the atmosphere as photosynthetic bacteria spread and thrived. To us, it’s the breath of life, but to these bacteria, it was a deadly toxin.
Luckily for these bacteria, there was iron that could react with this oxygen, keeping the atmosphere liveable for a while. That is, until the iron ran out and oxygen build up in deadly concentrations:
> The consequence was mass death among the planet’s abundant bacterial colonies – an oxygen holocaust that knocked life back down to nearly nothing. Only a few anaerobes survived, in isolated nooks and crannies where the deadly gas did not reach.
> After this catastrophe, the planet would have seen several million years of relative quiet. In this life-poor era, layers of silica minerals were deposited on the ocean floor. But in the meanwhile, erosion continued to free up iron atoms, which slowly scrubbed the atmosphere and oceans of oxygen.
> Eventually, the world was cleansed, and life bounced back, spreading from its refuges to once again cover the planet. Of course, this exuberance contained the seeds of its own downfall – bacteria still spewed out the waste oxygen that they could not abide – and the cycle repeated, not just once but many times. Each time, a layer of iron oxides was deposited, followed by a layer of iron-poor silicates in the aftermath.
It took almost a billion years before aerobic bacteria evolved and broke the cycle. Think about that: for about a third of the entire time life has existed on this planet, it was stuck in this self-destructive loop.
EDIT: What this story also shows is how much of Earth's geology is a result of the presence of life, and I recall reading articles of scientist trying to figure out if that could be used to detect the presence of life. Although I guess that measuring the chemical composition of the rocks on another planet would be even harder to measure than the atmosphere.
Abstract: Chemical disequilibrium in planetary atmospheres has been proposed as a generalized method for detecting life on exoplanets through remote spectroscopy. Among solar system planets with substantial atmospheres, the modern Earth has the largest thermodynamic chemical disequilibrium due to the presence of life. However, how this disequilibrium changed over time and, in particular, the biogenic disequilibria maintained in the anoxic Archean or less oxic Proterozoic eons are unknown. We calculate the atmosphere-ocean disequilibrium in the Precambrian using conservative proxy- and model-based estimates of early atmospheric and oceanic compositions. We omit crustal solids because subsurface composition is not detectable on exoplanets, unlike above-surface volatiles. We find that (i) disequilibrium increased through time in step with the rise of oxygen; (ii) both the Proterozoic and Phanerozoic may have had remotely detectable biogenic disequilibria due to the coexistence of O2, N2, and liquid water; and (iii) the Archean had a biogenic disequilibrium caused by the coexistence of N2, CH4, CO2, and liquid water, which, for an exoplanet twin, may be remotely detectable. On the basis of this disequilibrium, we argue that the simultaneous detection of abundant CH4 and CO2 in a habitable exoplanet’s atmosphere is a potential biosignature. Specifically, we show that methane mixing ratios greater than 10−3 are potentially biogenic, whereas those exceeding 10−2 are likely biogenic due to the difficulty in maintaining large abiotic methane fluxes to support high methane levels in anoxic atmospheres. Biogenicity would be strengthened by the absence of abundant CO, which should not coexist in a biological scenario.
The fermi paradox bothered me quite a bit, like all paradoxes and they should bother everybody. They are a flag that something does not add up and there must be some sort of wrong assumption somewhere.
As most of our combined "knowledge" does not add up correctly just one example is quantum mechanics and relativity - no, they do not add and therefor need higher dimensions to have a model (a emergency hatch).
It is quite funny when you understand that 2 general believed assumptions are the root cause for all the strangeness in our psysical models and very far down the line it explains why we will never receive alien EM signals in the area we a searching in - really makes no sense to scan there.
> It is quite funny when you understand that 2 general believed assumptions are the root cause for all the strangeness in our psysical models
Eh.. no? That's literally the opposite of how it works: it's not two strange assumptions causing all this weirdness, it's two very strange observed phenomena for which these two models give the best predictions, so far.
That is not what I meant. Both are objectively measurable results - of course if you look at critic voices the details in their implementation differ, but in general yes.
But there are different ways of implementing something and which one you choose depends on assumptions. If you use Field Equations for describing relativity you need a certain set of assumptions. If you use a different mechanism to describe relativity, you need another set.
We also have no reason to believe that we'd be able to detect other civilizations, even if there were millions out there. They might well be using other means of communication. Even if they were using the very thing we were looking for, it's still likely we would miss them - even if they were right next door to us. From SETI's FAQ[1]:
> If an extraterrestrial civilization has a SETI project similar to our own, could they detect signals from Earth?
> In general, no. Most earthly transmissions are too weak to be found by equipment similar to ours at the distance of even the nearest star. But there are some important exceptions. High-powered radars and the Arecibo broadcast of 1974 (which lasted for only three minutes) could be detected at distances of tens to hundreds of light-years with a setup similar to our best SETI experiments.
It always seemed odd to me that people call this a paradox.
From the perspective I gathered through understanding a very beautiful unified theory (not my model) - this is exactly my point.
EM waves as we use it are useless for long distance communications. I even doubt that those waves will still be detectable in a different solar system as the general assumptions that our vacuum is a very homogeneous is not true for me (the underlaying dimensions are for me, but not the vaccum as we know it). I have much more effects that cause disturbances of such waves.
Inside a solar system, there are also better techniques that are more stable in propagation then our Hertz EM waves. But unfortunately, we adopted a form of Maxwell Equations that are not suitable to describe the phenomena (the original equations in quaternion math can however). Nicolas Tesla did a lot of research in this area, but it is not very well known/understood. (From the model I'm using 3 forms are derived. As far as I dug into Tesla, he worked with 1 form. The 3rd form is the interesting one but very hard to produce /detect.)
It is a paradox in the sense that most of the educated guesses result in a universe which is very different from the one we observe. The paradox exists between:
1. the admittedly weak evidence for each of the guesses
2. and the evidence that at least one of the guesses must be wrong.
Calling them "educated guesses" is overstating the evidence. We don't have the datapoints to estimate how common life is or isn't in the galaxy by empiricism, and we don't have the scientific knowledge to derive the numbers from first principles. Divorced from reality, that means that the educated guesses are really "we come up with numbers we want and then bullshit an explanation for those numbers."
Another perspective is that, as we've understood better how our EM radiation percolates for space, radioastronomy basically can't find anyone who isn't in our solar system (except maybe if they directly try to talk to us). That means that even our failure to find life via SETI isn't evidence of anything.
>the educated guesses are really "we come up with numbers we want and then bullshit an explanation for those numbers."
tomayto, tomahto. You won't get a strong defense of most of particular values for the drake equation from me. The question that remains is which of our guesses are wrong and why?
>Another perspective is that, as we've understood better how our EM radiation percolates for space, radioastronomy basically can't find anyone who isn't in our solar system (except maybe if they directly try to talk to us).
There are other aspects of the universe that don't agree with common assumptions about how it should appear if it were swarming with technological civilizations with a billion year head start on us. For instance we have yet to detect any stellar/galactic engineering. Then again I'm not particularly convinced by our assumptions about a billion year old technological civilizations.
Fundamentally, there are four main responses to the Fermi paradox:
1. We really are the first.
2. Interstellar communication and travel is effectively impossible.
3. Interstellar communication and travel is possible, but is not executed in a sustained way for various cultural reasons.
4. Alien life exists, but we haven't or can't find it.
All of those explanations are very plausible answers. In fact, the notion that we "ought" to have found alien life by now is itself quite difficult to argue, because it relies on extrapolating estimates from 0 data points (note that we don't know how to become an interstellar species, and it's debatable if we even yet have the technological level to become an interplanetary one).
I'm going to try to put into words something about our methods of hunting for alien life that has always bothered me, and I'm probably going to fail.
What is intelligence in the context of extraterrestrial life? I posit that we have no good model for what intelligence actually is, and that it makes no sense to assume any alien lifeform would share our goals of seeking knowledge, reproduction, preservation, or "living well". These are goals tied up very much with how life on this planet evolved. What if instead of life being on a one-dimensional axis of "intelligence", each isolated biome evolves unique properties for continued existence on its own planet, with very little overlap? What makes our "intelligence" special or even desirable, outside of furthering our own evolutionarily programmed goals? Take those very specific goals away, and intelligence becomes something without a definition.
This leads to a more fundamental question. What is life in the context of extraterrestrial life? How do we define success for an alien lifeform? Its continued existence? ...But in what form? Over what timescale? On what physical scale? How do we even know if any life we may find is alive or dead? I think these are not pointless philosophical questions, but something that should guide our efforts. How would we even recognize life if we found some? Are we even looking for life, or are we merely looking for life similar to Earth? Surely Earth-similar life would be much more rare than just life, but we seem to think "life" will exist on other planets with function similar to Earth, if not form. Why assume this? A lot of Earth's life's functioning is derived from how it evolved and how it's composed.
I think this may be part of the answer to the Fermi Paradox. Perhaps it's a faulty assumption that intelligent life would want things like we do, and perhaps it's a faulty assumption that intelligence is even a real thing, in a context outside of Earth. Perhaps it's also faulty to assume that all life will have evolutionary goals similar to Earth's.
One softball answer to that is that any civilization that doesn't get off of its home planet is likely to go extinct, so there's less chance of it actively modifying the environment in ways we can detect. It's also less likely to need to develop long range, high powered communications that we can detect.
At the moment I think the idea that we're only looking for life that fits some definition of success is specious, we're looking for any life we can find! It happens that a big, spread out civilization that looks like us is more likely to emit something we can see, be it atmospheric, electromagnetic, etc, just by nature of being in more places in space and having a larger footprint.
There are astrobiologists who spend a lot of time thinking about what life may look like, but when it comes to where to put limited resources, we start with what we know to look for (us), and go from there.
You might be interested in the book 'weird life' by David Toomey, which tries to theorize about what some more exotic living things might look like in the galaxy, and expounds on some of these definitional questions.
I'm going to fail in my response too, since it's not my field. :)
Starting from the beginning of the search, there are some gases (like oxygen) which are pretty volatile and react with many things. If volatile gases and compounds are in the atmosphere, two possibilities exist:
1) It's young, and hasn't burned through all the reactions that its raw materials would present.
2) There's some process actively creating more volatile gases, which could be a sign of something akin to life, because it doesn't drop into an expected low-entropy chemical makeup.
People much smarter than I in the field would be able to distinguish more "non-living" sources like geological cycles than less-expected "maybe life" activity. But basically, if there's some life-ish process on the planet, it should affect the entire atmosphere enough to be detectable.
Certainly it's only 1 way that chemical activity can be detected, because if things are bound into subterranean caverns or don't involve gases in their activity cycles, it probably wouldn't be visible in its atmospheric composition. However, this sort of search doesn't necessarily target earth-like life, but any "huh, that's strange" observance of chemical makeups, which is good.
So we have one additional means of defining "life", in that it goes against the chemical entropy-reducing direction of its planetary environment; there are sustained complex active processes that aren't just raw chemical or physical potential energy releasing itself. If we find something "living", only then the question of whether or not it's "intelligent" becomes meaningful, because the only metric we currently have for that is "thinks like humans" which isn't enough to work with.
With existing technology it’s tough to detect oxygen on smaller far-away planets. However, what we could instead look for is a combination of gases that likely means presence of life on earlier stages, before oxygen becomes abundant in the atmosphere. (The assumption is that the alien life we might find would likely be on early stages of development anyway.)
This research is about how such a combination of gases—lots of carbon dioxide, methane, and no carbon monoxide—can be detected and told apart from possible nonliving sources. The new approach should be viable to apply using Webb telescope on smaller planets like the ones in TRAPPIST-1 system.
I think this is a step in the right direction, but it still has the central issue that looking for oxygen rich planets (or any atmosphere with a disproportionately high quantity of some suitable agent for reduction (respiration). We didn't even get around to the whole respiration thing on this planet for quite a long time, and there's no requisite that ATP/ respiration is the direction life is going to take, and equally, in the event of some kind of reductive respiration, there's not a prerequisite that oxygen be that agent, although its a pretty good candidate.
> there's no requisite that ATP/ respiration is the direction life is going to take
Based on the article I linked in my other comment I would say that on oxygen-rich planets, respiration is likely to happen simply because life needs to find a way to deal with it's toxicity, or perish. Although that presupposes that photosynthesis is inevitable, which also doesn't have to be true.
I kind of wonder how much we truly know about the strength of lock-in effects of evolution - of how much life is "stuck" with old hacks that we can no longer get rid of or that lead to dead ends. I doubt we'd ever evolve avian lungs from where we are now, for example. I know there are examples like that all over the place, but just how strong is the effect?
As one example on a physical rather than a chemical level, I read that marsupials are stuck for this reason. They need claws to climb into their mother's pouch after birth, so there are certain ecological niches closed off to them. You'll never see a hoofed marsupial, for example.
I've heard that the cheetah is considered an evolutionary dead end as well, being so hyper-specialised for speed that they are unlikely to be able to keep up the arms race with their prey, nor able to evolve back out of this.
I'm not a scientist by any means, but since childhood when I was first exposed to the fact that life on Earth needs oxygen (and many other things, in extremely basic terms) to exist, I've been thinking to myself what if there are other distant planets where life has bootstrapped itself from completely different (or maybe opposite) components and conditions. I'm sure someone with more knowledge than I in biology and physics would certainly be able to offer a good explanation or thought.
I think the problem there is simply the fact that it isn't knowable. If there is a way for life to be that different, how do you look for it?
My first statement is likely stronger than it needs to be. My main question back to you is, how do you look for something that you imagine may exist, but couldn't say how?
> My first statement is likely stronger than it needs to be. My main question back to you is, how do you look for something that you imagine may exist, but couldn't say how?
I certainly agree with you, thus seeking for life similar than ours is the only feasible way to spend time in deep space research; we cannot look for something different, because we don't know what to look for.
All those rule books, but it takes just one butt scratch on the way back from the interplanetary probe toilett to unfold this scenario. Poor europe.
Honestly, after seeing those anti-corruption rule books - and on the same homepages where they are displayed, the markers in countrys where you cant to buisness without - sort a contamination scenario in itself, i doubt that anything can prevent this once the dice with the one killing side gets re rolled often enough.
So my money would be on less philosophers employed, more disease-control specialists, which would quickly introduce counter agents that could be consumed by the local flora/fauna.
> Unlike today, there were no oxygen-breathing animals to expire carbon dioxide and close the cycle, and so it quickly built up in the atmosphere as photosynthetic bacteria spread and thrived. To us, it’s the breath of life, but to these bacteria, it was a deadly toxin.
Luckily for these bacteria, there was iron that could react with this oxygen, keeping the atmosphere liveable for a while. That is, until the iron ran out and oxygen build up in deadly concentrations:
> The consequence was mass death among the planet’s abundant bacterial colonies – an oxygen holocaust that knocked life back down to nearly nothing. Only a few anaerobes survived, in isolated nooks and crannies where the deadly gas did not reach.
> After this catastrophe, the planet would have seen several million years of relative quiet. In this life-poor era, layers of silica minerals were deposited on the ocean floor. But in the meanwhile, erosion continued to free up iron atoms, which slowly scrubbed the atmosphere and oceans of oxygen.
> Eventually, the world was cleansed, and life bounced back, spreading from its refuges to once again cover the planet. Of course, this exuberance contained the seeds of its own downfall – bacteria still spewed out the waste oxygen that they could not abide – and the cycle repeated, not just once but many times. Each time, a layer of iron oxides was deposited, followed by a layer of iron-poor silicates in the aftermath.
It took almost a billion years before aerobic bacteria evolved and broke the cycle. Think about that: for about a third of the entire time life has existed on this planet, it was stuck in this self-destructive loop.
EDIT: What this story also shows is how much of Earth's geology is a result of the presence of life, and I recall reading articles of scientist trying to figure out if that could be used to detect the presence of life. Although I guess that measuring the chemical composition of the rocks on another planet would be even harder to measure than the atmosphere.
[0] http://www.patheos.com/blogs/daylightatheism/2009/02/bands-o...
[1] https://en.wikipedia.org/wiki/Deep_time