The thing is, life has almost infinite time to evolve out of these various elements. The fact that it didn't evolve here on Earth means absolutely nothing, seeing as Earth alone has billions of years left where such life could arise, and there are literally countless planets everywhere in the universe where the random dice of evolution roll every second.
Except the ratio of hydrogen to deuterium is a function of astronomy and more specifically fusion. No naturally formed planet is going to end up with that imbalance. Which means no natural deuterium based life forms. So while some alien civilization create deuterium life, it’s not going to be part of natural ecosystems.
And so it goes for most possible interesting edge cases. Dependency on rare elements like Neptunium means any competitors without that dependency have huge advantages.
On the other hand if proto life is extremely common then silicon proto life might always be out competed by more efficient alternatives. For example the fact Silicon dioxide is a solid where carbon dioxide is a gas is a major advantage or using carbon.
Hybrids are a different story, but I doubt that’s what anyone is talking about by silicon based life forms.
You don't get to constrain alien life to your preconceptions. Even some Earth life secretes SiO2. Using carbon for some things would not invalidate its Si-basedness any more than diatoms have given up carbon-basedness.
Silicon's near absence from our favored solvent, like iron's, is a product of toxic levels of biogenic atmospheric oxygen. Our early oceans were saturated with iron products, and are now starved of them. There is no reason to assume oxygen would be their favored oxidant.
That goes back to astronomy no other option is going to be nearly as plentiful.
> You don’t get to constrain alien life with your preconceptions.
It’s not a preconception it’s the solubility of silicon and silicon compounds. Yes, CO2 and SiO2 aren’t the only option for respiration, but CO2 was and is a near endless supply of carbon and oxygen. Without that growth simply slows down dramatically. Even with a photosynthetic equivalent you simply don’t get the great oxygen event from silicon lifeforms in even 10 billion years.
PS: To be clear I am not saying silicon life would be impossible just that it’s at a huge disadvantage head to head and would have a vastly slower progression to large scale multicellular life.
Carbon is a good choice for our temperature range, but there are plenty of temperature ranges as well or better represented. Life will not sneer at the others. Most life on Earth cannot make any use of the carbon in CO2, no matter how much of it there is; in fact, the more of it there is, the worse off most living creatures are, only green plants excepted. You would die in a room with the nitrogen replaced by CO2, despite that you use none of the nitrogen at all. (Only bacteria can "fix" nitrogen, and only some of them.)
Iron is very plentiful in the cosmos and in Earth's constitution, and most life depends on it, but it is practically nonexistent in the open ocean; yet life thrives there. Even where iron is plentiful, life uses hardly any. Silicon is extremely plentiful, too, yet used by our life even less -- until just lately!
So, your argument from plenitude utterly collapses. Life as we know it is a product of history and circumstance. Given different circumstances and different history, you should expect a different product. There will certainly be similarities dictated by physics: e.g., cells are very, very likely, and equally so use of liquids. Aperiodic fibers to encode genes, cognate to our DNA, and others to fold up and carry out processes, cognate to our peptide chains a.k.a. proteins, are quite likely. But there is no reason to imagine that any of the details of the encoding would match.
That’s a huge misconception about biology and evolution. Basic cellular biochemistry is extremely well conserved. There is almost no pressure to use more iron, but significant pressure to use less. Photosynthesis for example is Iron dependent and that acts as a major limiting factor on ocean ecosystems. Yet, we don’t have an iron free alternative adapted to utilize that giant ecological niche. Life is seemingly using as little as possible.
That should suggest why primarily silicon life is such a poor option.
> There are plenty of temperature ranges as well or better represented.
For complex life it’s not just about temperature but also pressure and access to sunlight. Anyway, the normal argument is that silicon based life could thrive in extremely high temperatures. That’s all well and good for silicon but not so much the other chemicals it’s interacting with. Life is dependent on being able to reliably create and break relatively weak chemical bonds. However, when you start to look at the actual chemical options at those temperatures you run into serious problems. The kind of large molecules you want for complex life are either unstable or too stable at those temperatures.
We don't know of many interesting Si compounds specifically because we have none of the organisms that would produce them. Our ignorance does not constrain nature.
"Weak", for bonds, is exactly a function of temperature. At higher temperature, life will have chosen constituents that bond with the right strength, wholly ignoring your preconceptions of what it ought to be using.
Anyway, Life can only chose chemical bonds that are possible. It’s perfectly reasonable to pick a specific temperature range and say here this is ideal for silicon lifeforms, but that means every chemical interaction must occur in that temperature range which is a major physical constraint.
We don’t know of many interesting and relevant Si compounds in large part because they don’t exist. It’s not even just chemical compounds life needs a water equivalent for all that cellular machinery to float around in and bump into each other.
Nature is not constrained to the limits of your imagination. I am frankly surprised to find you continuing to insist it is.
In the end all of chemistry comes down to quantum mechanics it really is quite constrained. Put another way you can list our every possible 2-9 atom molecule containing Silicon plus common elements and look at how the behave.
You are just making things up. Who do you imagine believes you? Why do you want them to believe you?
People have explored some of this space and found nothing.
At room temperature. Silicon life, if it exists, would be basically using lava instead of water. Glassblowers work at 600 degrees, i imagine thats the sort of temperatures where we will see any silicpn chemistry take place at non glacial pace
Net result you might get the equivalent of very simple multicellular life, but intelligence becomes extremely unlikely.
Chlorophyll photosynthesis does not work well at high temperature, but that says less than nothing about whether photosynthesis of different products using a different molecule and a different process could evolve. What we can say is that if it could, it would, somewhere.
You have no basis beyond your own preconceptions for any statements about likelihood. Thus, your estimate is 100% confabulation.
Silicon tetrafluoride might be a gas, but it’s not going to be plentiful. If you feel there are real options here feel free to list em.
> that says less than nothing about whether photosynthesis of different products using a different molecule and a different process could evolve.
Carnot efficiency does. You can’t simply scale up temperature and expect equivalent efficiency.
In case you didn't know, Earth has about one billion years of water left.
https://www.sciencedaily.com/releases/2013/12/131216142310.h...
by definition, the most probable form of life in the universe is the 1 we are observing. you only need math and probability to figure that out. We also have observational evidence. As far as we can tell, there is no other life in our solar system. We have 8 other planets and many moons that have failed at creating life in any form - that's literally hundreds of billions of years of failed attempts at life.
you can't just pick an element and think its going to work. you need ALL the elements, ALL the states of matter, and the right ratios and amounts of elements to work. Even if you get that lined up, expecting complex life to form under enough pressure to create diamonds in thousands of degrees centigrade also puts the probability of complex life off the table.
I don't known who this is hard to understand. in the simplest example as the article states, if you want to fly, there are things that necessitate something that will fly, such as wings. no wings, no fly. sure its POSSIBLE you can fly without wings, but UNLIKELY. given that we have multiple lineages of evolution taking different paths that end up with the same solution is evidence of that.
The Earth is the edge case, is the point we're making. All of the conclusions and deductions about what life must be like elsewhere that use Earth as their implicit foundation are going to be overfit to the data, so to speak. Organisms on Earth converge to similar forms: dolphins and fish, bats and birds, for instance, so the form is useful on Earth is a valid observation. Therefore, we can expect to see these forms throughout the Universe is a quite a jump.
You do not know that. All available evidence points to the opposite: We have no knowledge, not even a hint, of any other physical process that could sustain life than that of Earth's carbon-based chemistry.
The idea that life could take a myriad of different forms is beautiful, but it is pure fantasy, based on no evidence at all.
Again, how can you be so certain of it? Life could have existed in some form on Mars or Venus or even Mercury millions if not billions of years ago, only to be extinguished by the changing conditions in the solar system and ground to absolute dust by time. Maybe not advanced space faring civilization, but life could have existed in those places and you simply don't know.
>> you only need math and probability to figure that out.
Yes, and maths and probability are telling me something very opposite to what you are saying. That if you are observing a solar system like ours(forget the entire universe for a second) for a ~100 years out of billions of its existance, then sorry, but you don't know anything about it, certainly not if it harboured life in the past or not, not to a degree that you seem to be certain of.
Buoyancy in water is different than in air. Lighter than air natural controlled flight, even in a relatively dense atmosphere like Earth or Titan, is highly unlikely. Fish maintain buoyancy with oil in their livers which is a relatively low energy process.
Hot air balloons and other LTA vehicles work by having a mean density lower than the containing medium e.g. the atmosphere. Even with Earth's relatively dense atmosphere there's not a lot of lifting gases that are effective without significant heating. Definitely not readily made by biological chemical processes. That leaves thermal balloons. The amount of energy to heat the air in a hot air balloon is pretty significant and requires energy dense fuels.
So a hot air balloon animal would need to produce and then burn energy dense hydrocarbons and have a strong yet lightweight natural gas envelope and body structure that could handle the burning of that fuel. Burning I would note at temperatures that would sterilize surfaces.
Not balloons perhaps, but spiders float on strands of silk using very similar principles.
Pollen and seeds frequently use some kind of floating device to spread as far as possible - again, you probably wouldn't call it flying as such, but they can move through the air for the purposes of reproduction without having wings.
2. Buoyancy in air has been achieved with an industrial level of success using hydrogen. Producing hydrogen is easily within the energetic range of biological processes. Air-buoyant animals could have existed for millions, even hundreds of millions of years before being outcompeted by pterosaurs and birds, and then left no trace.
Sharks are fish, so this clearly isn't categorically true. You probably mean either bony fish (for which I think it's kind of questionable that its true) or more specifically lobe-finned fish (for which the case is stronger.)
“Fish with air bladders do not, in fact, use oil in their livers for buoyancy. They have an ‘air bladder’, which you may read about. [...] Fish with air bladders are much more closely related to you than to sharks, so it is a big error.” is critically different than what you actually wrote upthread, and is obviously kind of silly. It also would have made no sense in response to the post it responded to, which also referenced “fish” in general and not “fish with air bladders”.
It could be that silicon based life is in fact constrained by temperature and can only arise in planets where the mean temperature is in the thousands. This could in fact mean that we do have a parallel silicon based biosphere underneath our feet. There is obviously no evidence for this whatsoever but then again, there is no reason to assume that the occasional leakage in the form of volcanic eruptions would leave any trace that we could use to deduce that these samples were once living entities.
I'm at best doubtful about life on Mars because I find it hard to imagine some form of life that occupies a small part of Mars i.e. it's only in the parts we haven't seen. I tend to think if there's any life on Mars it'll find a way to deal with the conditions on all of Mars. By the same token if there's any silicon based life then it'll pop up in places that we can find as well as those we can't. Maybe it does best in places we can't but surely there would be some oddball silicon based creature that would beat the odds.
The macro example would be the extinction of the South American marsupials when the North and South American land masses merged. All the placental animals in North America went south and all the marsupials in South America went extinct. Except for Opossums which for whatever weird reasons not only survived but went into North America.
We have no evidence of a void ecology in near earth orbit or of life persisting close to the Moho barrier - where the crust meets the mantle. There are hard limitations to the encroachment of life that only technology or radically different chemistry can circumvent.
The same hard barriers might also mean that life on Mars is largely constrained to those few underground liquid water lakes that we have recently found evidence for. Keep in mind that even the most barren deserts on Earth have several orders of magnitude more water present in the air than on Mars.
Other areas that are similar, sure. But if you're asserting that we can be confident there are no subterranean mantle-creatures because we don't see any wandering about out here, I don't think it's a good argument, for the same reason we can't go down there ourselves and look
Like, if it failed to do so, it would fail the definition of life? I don’t think anyone defines life that way, and I don’t think it would be a good definition (would I even count as alive under such a definition? It seems like no.)
For all that after several billion years it's just carbon based life forms in these parts. You'd think that there must be some area where silicon based life would provide an advantage. Unless it's a case that carbon based life is an overwhelmingly superior product but on some hypothetical world it's simply filled with silicon and there's virtually zero carbon.
Additionally we find organic molecules everywhere from comets to gas clouds in galaxies. We don't really find as much interesting silicon-based chemistry everywhere.
We have only a single very specific data point. That, and the human tendency to opine confidently about that which we cannot know.
Just give it a few more decades ...
The common ancestor of octopods, insects, and humans had eyes, and coded where to put them with the same gene in all lineages that have eyes. This was demonstrated by inserting a vertebrate "eye here" gene into a fruit fly embryo, causing an eye to grow there.
Think about how some LCLLAS talked about how silicon life is probably a thing. First off, it it were, given Earth's crust is mostly silicon and its the most habitual place ever discovered, it would have evolved here. but it didnt. It turns out silicon is just too ridged, and to get life going you need all sorts of chemical properties that just aren't congruent to life.
We are carbon / oxygen organisms for a chemical reason. despite the availability of other resources, other forms of lifeforms didn't develop for a reason. maybe other forms of life does exist in some methane ocean on Saturn like planets, but its not going to be very complex, and definitely not intelligent life building space ships.