* We are on the outskirts of the Milky Way because the center of the galaxy is radiation hell. A chunk of most galaxies is too "hot" for life. So take most of the SPACE out there and move that to the side.
* The planet itself has to be around a star that's not too big and not too dim, at the right distance, of course.
* Our Solar system is very special as it has the planets in stable, almost circular orbits around a SINGLE star. It's not "collision central", where most planets can still smash into each other, within a binary star system, to boot.
* We have gas giants, by chance, protecting us against space rocks flying into us.
* The Moon, just the right size, just the right distance, to keep us in stable rotation, with seasons.
* Just the right amount of water. Too much or too little water, and we would not be here.
* I am probably missing a bunch...
* And only then you get to the rest of the factors for life to be possible.
If anything, what you bring up kind of goes right along with my point! There may be life out there, but what is life, or intelligent life for that matter? How would we know what we were looking at if we even saw it?
> How would we know what we were looking at if we even saw it?
We try very hard not to see it!
The article mentions "toxic atmospheres", but oxygen was toxic to 99% of the existing life when it first started increasing on Earth. Life switched strategies to use it instead of choke on it. "Toxic" is relative. The other factors you mentioned may have similar issues.
Some bacteria can thrive under high radiation because they have four nuclei and related error correcting. It costs some energy to have that feature, but that's not a show-stopper to the critter.
My pet theory is that there have been many places where life took root, in very simple form, but failed to hit the "home run" like the Earth did, because the other factors stifled it.
Such efficiency issues may not matter to modern humans. However, changing that would be too big of an upgrade to our current system to simply bluntly "add".
Imagine a puddle waking up one morning and thinking, 'This is an interesting world I find myself in, an interesting hole I find myself in, fits me rather neatly, doesn't it? In fact it fits me staggeringly well, must have been made to have me in it!'
I wouldn't mind an explanation on that one, seasons are a result of the axis tilt of the planet, not something to do with the moon.
The moon's orbit acts to keep the Earth's obliquity in a very tight range, between 22.1 and 24.5 degrees (where 0 means perpendicular to the plane of the Earth's orbit).
Keeping that obliquity angle range keeps the seasons roughly what they are, avoids the extremes that come with a 90 degree obliquity, and stabilizes climate. An obliquity angle of zero might work too, but I think life on Earth is much more interesting with seasons than without.
Without the moon it would have just sat stagnant.
This creature still lives like that:
Your definition and data for life is only the current life on Earth, since we don’t have a clear understanding of other types of life in the universe we cannot fully support this hypothesis.
This is an assumption. I might have to read the book you linked, it looks very interesting, but I think lifeforms that have evolved to not use hemoglobin in their circulatory systems isn't that far of a stretch.
Heck, what's stopping us from classifying ocean currents as a sentient lifeform?
Can't wait to finish what I'm reading currently to get started on Children of Ruin.
Section 6 of "Why Philosophers Should Care About Computational Complexity": https://www.scottaaronson.com/papers/philos.pdf In the context of the rest of the paper, of course.
and the actual paper is here: https://iopscience.iop.org/article/10.3847/1538-4357/ab1d52
phys.org: just say no.
It's like sitcoms with laugh tracks. Everyone you ask hates them, but if you ask people how much they enjoyed/would rewatch/would recommend/... a certain show they consistently give higher ratings to an episode with vs without canned or study laughter.
(CO is much more reactive, but it's harmful to us because it reacts to our hemoglobin in much the same way as oxygen. So since Earth life has managed to get on just fine with all this corrosive oxygen around, the same argument may still apply.)
EDIT: "Especially in combination with water vapour in atmosphere - it would freeze, static charge would build up between the ice particles and the discharge would ignite everything. Indeed the fact that O2 is so high is a proof that there is nothing left to burn"
The fact that there is excess of a reactant really means that there is an ability for interesting reactions, and therefore life. Ash cannot be animate because it’s (basically) at ground level and does not have the free energy to do anything.
I swear, this is an exact line from a Ray Bradbury story that I read as a child.
Of course, that's a completely different argument from the one the researchers had.
First plants caused ice ages, new research reveals : https://www.sciencedaily.com/releases/2012/02/120201094923.h...
Like you mentioned, CO is bad for us because of our hemoglobin. Otherwise I could imagine life using an otherwise chemically interesting molecule like CO (it can oxide further).
CO2... not so interesting. Aside from the reaction to make CaCO (?) and acidic when dissolved in water it’s quite limited being fully oxidized.
You need the ability to make things out of your molecules. Stuff at the ground state are boring!
Plants expand energy (otherwise wasted sunlight) to convert CO2 into O2 to make an interesting molecules, namely starch with which they can do something. If they had an endless supply of starches, they wouldn’t have bothered evolving with photosynthesis - just like we don’t care for photosynthesis since we have plants.
Essentially the point is to be self-limiting. No one is saying "Planets outside of these parameters can't have complex life." but instead "Planets outside of these parameters could not give rise to what we know as complex life."
Why would life depend on the low concentration that is not even toxic to all of the life here on Earth?
It wouldn't, and the study isn't saying that it would.
The point is about narrowing the search space. An analogy would be guessing passwords. If I want to guess the passwords of the people I work with I can start with the assumption that it could be anything, which doesn't narrow the space and makes the task impossible, or I can start with the assumption that it'll be based on a dictionary word with some numbers because all my passwords are like that. I'll definitely miss some passwords that don't fit my assumption but I'm far more likely to get some positive results (assuming my way of generating a password is common in the universe.)
Take the CO criterion, for example. While it is reasonable to point out that CO may be present in high concentrations in many planetary atmospheres, at levels that would be toxic to life evolved on earth, one must consider that life might evolve in a way that tolerates or even exploits it. Oddly, the authors acknowledge this, yet, apparently without any counter-argument, still include CO as a probable show-stopper.
As the way to search for life beyond the solar system is to look at atmospheric composition, an alternative way to look at the 'CO problem' is to say that an abnormally low CO level on these planets might be a hint of life.
Given the amount of real estate in the universe that is "out in the cold" (Oort cloud equivalents, way beyond the snow line) it may be that we are the oddballs, and there are scientists out there wondering how life would be possible with molten ice and burning things with something as hellishly reactive as atomic oxygen. Free-floating planets might be where the really good parties are in our galaxy.
Outside of the matter that we are made of, who knows. It's not impossible that dark matter could somehow be set-up to create life, but we've no idea if it's feasible. The same goes for dark energy, only more so as we have basically no clue what dark energy is, even though it makes up the majority of the 'stuff' in the cosmos.
When life started here CO2 was from hundreds of thousands to many millions of times more abundant than it's now. Tens of thousands more of it won't probably even make oxygen respiration impossible.
Other extremophiles and archea exist and have been observed in deep caves and rocks. Life really does find a way!
I guess isn't silicon the only other that bonds four ways? Not a chemist but I feel that 4 bonds are a big thing.
Between them, carbon and water have a bunch of unique properties. AFAIK, its hard to come up with any other suite of materials offering the same prospects for complexity, at any temperature.
Also I don't see why you couldn't have an organism that "breathes" solid material.
> Silicon dioxide melting point: 1710 °C
No complex chemistry can survive these temperatures.
SiO2 is only soluble in HCl and HF, which are very reactive, so no solubility either.
> Also I don't see why you couldn't have an organism that "breathes" solid material.
All of known biological chemistry relies on some sort of solubility for reagents. I don't think there's any known organism that can get rid of solid waste from the entire volume of the organism.
You can also have chlorine as your oxidizer and make Silicon tetrachloride which melts at −68.74 °C and boils at 57.65 °C, that temperature range is perfect.
What else will change by having a chlorine instead of oxygen atmosphere?
Life didn't evolve to breathe nitrogen, oxygen, etc which we just coincidentally had - it evolved to breathe and utilize what was already present on our planet. And this should be the assumption for all life, which means that restricting stuff because it would be inhospitable to us is completely nonsensical.
That's the point. When you can't find your keys at work, there are a wide range of possibilities - in reality, an infinite such number. But they're probably somewhere in the clutter on your desk.
Anyway, I'm reminded by this quote by Douglas Adams (veers off to something else entirely but it starts very relevant):
Imagine a puddle waking up one morning and thinking, "This is an interesting world I find myself in — an interesting hole I find myself in — fits me rather neatly, doesn't it? In fact it fits me staggeringly well, may have been made to have me in it!" This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, it's still frantically hanging on to the notion that everything's going to be alright, because this world was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise. I think this may be something we need to be on the watch out for. We all know that at some point in the future the Universe will come to an end and at some other point, considerably in advance from that but still not immediately pressing, the sun will explode. We feel there's plenty of time to worry about that, but on the other hand that's a very dangerous thing to say.
In a lab we can reproduce these combinations in ideally a much greater number. So my insight is that we can create chemical processes in a lab at a much higher rate and with much more interesting combinations that nature can. And still life hasn't arose in the lab.
This seems to me like a sensible experiment that can somewhat prove that if we can't do it in the lab, where we're free to combine whatever we want, then why should it be "easy" for nature with its limited amount of combinations.
But with any combination you try in the laboratory you get a very similar brown goo with a similar chemical composition. There are few atoms that are common and like to stick together to form molecules, so you get mostly some molecules with C, O, N, S, P, and H. Carbon atoms are happy to form long molecules. If you add a lot of Nitrogen atoms in a molecule, it is usually a good explosive and will react spontaneously (at low concentrations it only self destruct, it is difficult to get high concentrations and get an explosion). If you add a lot of Oxygen atoms two of them may decide to pick a Carbon atom and go away, something like
molecule --> CO2 + smaller molecule
In this mix you get the building blocks of a lot of important current biological molecules, IIRC you get all the building blocks of RNA. RNA is a weird kind of molecule because they can induce reactions in other molecules and they can sorta self replicate like DNA. So one of the hypothesis is that the first life like thing has/was a bunch of RNA.
Life on Earth needed like 1 billon year to appear https://en.wikipedia.org/wiki/Life#Origin . So for an undirected a
experiment you need 1E9 years x 5E14 m^2, instead of a graduate student that has only 4 years x 1m^2 x 1m if s/he is running the experiment in a giant reactor instead of a beaker. That is a difference of more than 23 magnitudes orders.
For a directed experiment, nobody really knows. Perhaps the firs step is to get a lucky RNA of length 20 and you must try the 4^20 combinations until you get a crappy first version of a self reproductive RNA, that is not very good and only can make a good copy per year. Can you call it alive? Is this really the first step? Perhaps its length is 40, that needs exponential more combinations. The initial RNA had probably more than 4 bases, so the search space is even bigger and more difficult to estimate.
Perhaps the first step is to create small soap-like balls and put them near something like a thermal vent that release H2? Perhaps the first "life" form use some sulfur compound to get energy? Nobody is sure.
We ~may be able to focus search on life sustaining chemical combinations ?
It seems like a fun time for this field
At the low end, the article is talking about 10,000 ppm (0.01 bar), so not much higher.
Nope! Imagine a shell around us, defined as "how far we could go, if we left right now, traveling at near the speed of light, given that the accelerated expansion of the universe keeps making things get further away." It's a large, but finite, sphere. It's actually smaller than the Cosmological Event Horizon , which is the cutoff point, beyond which light can never reach us (again, because the accelerated expansion of the universe is effectively putting space between us and the event faster than light can travel) - estimated to be ~ 16 billion light years in radius.
If by "universe" you meant "observable universe" - that's fair, but still no. How long could humans conceivably last before we go extinct, or change into something that can't be called human anymore? I feel like 100,000 years is an absurdly high estimate, but let's got 10x higher.
If we figure out how to travel at c/2 soonish, and we say going somewhere counts as "exploring" (no need to report back to any one), then we have a ~500,000 light year radius sphere to explore. That's ~ 225 billion stars. For the near ones, we can shuttle back and forth, but for the far ones, that's a one way trip. So let's say 100 billion space ships. And that's if we leave tomorrow.
c/2, 100 billion space ships... If we start paring these back to reasonable figures, you start to realize: our species will barely scratch the surface of the observable universe. In 1,000,000 years, I think, best case, we can cover a 50,000 light year radius sphere. That's 0.000000000000003% of the observable universe.
Also coincidentally the percentage of equity most startups grant engineers.