Is life an extremely rare thing in the universe?

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Carbon and silicon are the must combinatorial of the elements. 4 electron bonds.

ruveyn

It is arragant of us to think with are the only. Planet with intelligent life on it.

In a certain temperature and pressure range.

N and others in its group, have 3, that can be functional.

It depends on Temperature, pressure, and availability of the elements. The best semiconductor for microelectronics would be Germanium, the best metal for soda cans would be platinum.

Silicon probably doesn't actually work as a substitute for carbon in creating another class of organic compounds.

Basically, as atoms get heavier, they also get larger, and the length of the bonds that they form with other atoms are necessarily longer. On of the features of carbon that makes it so versitile is that the relatively short length of the bonds that it creates allows for the creation of double and triple covalent bonds, and the strength of the H-C bond, that makes the molecules stable. These are both properties which silicon appears lack.

So while silanes (the silicon analog of methane and more complex hydrocarbons) exist, silanes react readily with water, breaking down quickly, unlike hydrocarbons which are more durable. Even when you bring in oxygen to make silicones, which are much more stable than silanes, they are still nothing like as stable as hydrocarbons. When silicone is formed into a ring analog of benzene, it is not a flat ring, like benzene, and it does not demonstrate the same aromaticity (though, it does seem to demonstrate different kinds of electron delocalisation).

It bears noting that silicon is much more abundant on earth than carbon, yet no complex silicon based analogs to the hydrocarbons have ever been observed. That strongly suggests that even if these molecules are possible, the presence of carbon and water will favour the creation of the more stable organic compounds as we know them.

Now that's not to say that in an environment devoid of carbon silicon based organics couldn't arise, but their rectivity with water still presents a problem that might likely prove to make complex organic molecules impossible. Or at least much more improbable than the already rare organics as we understand them.

That pretty much sums up my views on the subject. Out of all the planets in the universe, the chances of life existing on *one* planet only are staggeringly slim.

Lack of imagination.

who talked about organic compounds?

You can use an entirely different fluid then water. You can chose what ever you need. Seriously, anything you need.

You reduce the temperature, and unstable stuff become stable enough. Seriously, any temperature you need, any pressure you need.

here some speculations
http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry

There's no proof that an other biochemistry is viable. The point is, that the possibilities are almost infinite. So there's certainly other viable biologies, then the water/C that we have on earth.

I think it's probably semi-precious but not extraordinarily rare or anything.

That Wiki article is an excellent reminder that other possibilities exist. If you assume that all complex chemical systems try to exist at as low an energy level as possible what is the -most probable- chemistry of life? I wonder of a quantum physical criterion can be invoked to see if our "carbon chuavanism" is justified or not.

I keep thinking of what Shakespeare wrote: There are more things in heaven and earth, than are drem't of in your philosophy.

ruveyn

ruveyn

Pay attention. I was responding to a fairly specific speculation around the substitution of silicon for carbon.

But let's move into the hypothetical. First of all, let's limit ourselves to chemical life. If we are positing life based on some alternative method of fixing and using energy, then we are moving into a scale that we probably could never recognize as life, let alone interact with on any meaningful level.

Now life requires a few basics: the system must be able to take energy from the environment, fix it, and then used the stored energy to power its activities. In organic life, that is based on chemical properties such as the mutability of carbon bonding, the strenght of C-H bonding, the aromaticity of organic compounds, and the electrical polarity of organic compounds (not the least of which is water). In another form of biochemistry you need to replicate these same properties. You need chemical bonds that are durable enough to hold until fairly specific processes break them, and free up some of the energy in those bonds as lower energy compounds are created; and you need a reverse system where energy from the environment is accumulated in order to build up those lower energy compounds back into the high energy compounds in which that energy is fixed.

And this is where all those hypothetical biocehmistries run into problems, because they present bonds that aren't durable enough (e.g. Si, P and S), they present an energy cycle that would be deficient at some stage (N-P), they are relatively less abundant than Carbon (Si, B).

Now I don't say that a system of analagous complexity is impossible. But I do maintain that a system of analagous complexity will not arise in an environment in which Hydrogen, Carbon, Nitrogen, and Oxygen are present in relative abundance, and in which temperatures suffice for the creation of organics. By their stability, they will outlast and become superabundant to any other analagous class of complex molecules.

I don't lack imagination--I'm just practical about what's out there in the universe. Other things are possible but as environments cool, those other things are going to get out evolved by carbon. Bottom line, hydrocarbons are more efficient than any other hypothetical biochemical process--and nature always prefers more efficient processes to less efficient one. And there's a lot more carbon and hydrogen out there than there is of any of the other candidates.

If life on most habitable planets is seeded via panspermia , it might be more common than if life has to emerge from non-living matter in every instance.

The next clue is to see how common Earth like worlds are. That should be revealed in the next decade or two.

After that we need to image their atmospheres. That's also in the next few decades. We could build the scope now but both NASA and ESA have mothballed their current programs dealing with this for lack of funding.

Why would we search for Earth like planets if we search for life? We already know that life can exist in conditions that are pretty much impossible for most known life to survive in. Life does not need to be similar to us, or anything we know.

There is reason to believe that planets with water and carbon exist all over the galaxy. And they probably exist in other galaxies as well, assuming the laws of physics are uniform everywhere. For that reason it appears very plausible that life should exist in many places.

However the only place we know for sure where life exists (at this juncture) is right here on our planet.

ruveyn

And how would we go about searching for life that we don't understand?

The next steps involve looking for things we understand.

I'm not sure it's correct to say it only originated once. There's evidence of massive die-offs and extinction events. We don't know that it's only originated once on Earth.