Why ET life is carbon based

Here's a paper entitled "Can Silicon Based Life Exist," explaining why extra terrestrial life is probably carbon based rather than silicon based. There are good web references at the end of the paper. The paper is from the University of North Carolina at Charlotte Center for Mathematics, Science, and Technology Education (http://www.cmste.uncc.edu/).

This link is an html version of the paper for safety reasons. The real document is of higher quality and has figures, but I'm assuming that people won't want to download a document from an unknown source. If you want the .doc link, ask me.

http://216.239.53.104/search?q=cach...oc life valence carbon silicon&hl=en&ie=UTF-8

 

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this is probably me missing the point here, but what does it matter whether a life form is sillicone or carbon based??
its still a life form right?
i am also assuming that their bodies would work in a similar way to ours, (if not the exact same shape)and im sure that any life form silly enough to let us experiment and cut up its people to see what they are made of, would not be able to develop the technoligy to come visit us anyway!

 

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Why would ETI be limited to carbon as their base eliment? Us humans that are from Earth are carbon based, and any creature with origins from Earth would have DNA markers specific to their point of origin.

North Carolina is an interesting place for an article about ETI base eliment to come from. Isn't North Carolina in the region of the Carolina Bays?

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what would be the difference between a silicon based life form and a carbon based life form ?

 

well, since there is no data for this subject. one must speculate on how life originates. is there only one possible way? or multiple ways?

given what we know about life here, some predictions can be made. these predictions are based on physical and chemical properties of the universe, and so are general properties, not limited to earth.

1) we can predict that any life origins must be carbon based. some of the reasons for this prediction can be found in the paper I cited as well as references within that paper. given this prediction, the search for life is considerably narrowed, which increases the liklihood that we'll be successful in that search.

2) given that life elsewhere will be carbon based, we can predict that it will be protein based. simple amino acids have been found to generate in laboratory conditions and have been found in asteroids. since amino acids can be formed spontaneously, these simple amino acids may have formed simple polypeptide chains which could have been the precursors to the first proteins.

3) given a protein world, does this necessarily lead to an RNA or DNA world? I don't think so, cause any molecule that could produce proteins and replicate with fidelity could fit this role. maybe something we haven't seen before, or maybe DNA-like or RNA-like molecules. who knows, but simple RNA chains have also been found in places where there is no life, asteroids for example.

Questions like these form the fundamental studies of astrobiology and are some of the questions NASA is asking in its exobiology programs.

 

nice one..

 

It is just possible that most life in the universe is not carbon based and does not use water as a solvent;

consider this; one possible way that has been proposed for humanity to explore distant stars is to build self replicating, autonomous machines; this may have already been tried, in some distant galaxy long ago and far away.

The universe might be slowly filling up with these Von Neumann machines, which (it seems to me) display all the characteristcs of primitive life forms.

Depending on how well they are programmed they might not be so primitive; they might even have been given the potential to evolve, and so may mutate into a myriad forms throughout the universe.

A lot of maybes, but it is possible, either now or in the future.

If these Von Neumanns are silicon based then the predominant form of life in the universe may well use little water or carbon in their 'metabolism'.

Just a thought.
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if it's possible, one needs to show how it's possible. what's the energy transfer, what are the redox molecules, what're the structural molecules, what're the information storage and/or replicator molecules? Could these potential molecules be created? Are they stable?

my contention is that Si could not be the basic element in the formation of life as C is for earth life, the conclusion being that ET life will also be carbon based.

Also, Why do you consider man-made machines life?

 

That is the point; robotic life is unlikely to emerge from abiogenesis, like the life forms on our planet; but if a carbon based lifeform evolved on a distant world millions or billions of years ago, invented Von Neumann machines with the capacity for evolution, then sent off them into the universe, they might be he most common form of self replicating complexity in the universe by now;
they might be the first such signs of life we discover.
They are as likely to be made of carbon as silicon, to be honest, or a hybrid of the two; but they may well be entirely different in 'metabolism' to natural organisms.
if that is not life, what is?

 

are you asking me to explain to you why man-made machines cannot be considered life?

i could do that, but it's beyond the scope of this thread. let's stick to natural life origins.

 

I assume silicon exists on cold temperatures, which would make them cold and slow. I've read about that a long time ago, so I might be wrong on that...

If life can be formed using any kind of molecules, than life is very likely to exist all over the universe. If life can only be formed through carbon, than it is less likely to be abundant.

Not necessarily. There may be quite different forms of life out there....


Still, even if life is only possible with carbon oxigen and water, it is still very likely that there is life out there. Think about it. What is a white dwarf made of? Carbon, Nitrogen and Oxygen! And they are actually quite common substances, eventough percentage-wise they seem quite little. Also, the most common kind of stars are the G stars (and close-by), which are sun-like. Most stars in the universe weights around 1 solar mass, which makes the sun a quite common star. Also, Eart-like planets are being proven to be more common than expected at first. Soon, life won't seem so rare anymore....

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Well, the Drake equation only works for life similar to ours. It works for finding ETs that are human for all intents and purposes. If you want to turn that theory on its head, fine. But you're throwing out alot of very safe assumptions. For instance: when it comes to methane-breathing intelligent blimp civilizations living in gas giants, why aren't there any in the clouds of Jupiter? When it comes to rock-munching mineral-based dwarves living on Venus-like hell planets, why aren't there any basking in the acid rivers of Venus?

I know it's hard to extrapolate a theory using a sample population of 1. But this solar system is all we've got to go by. If any of these exotic species did exist, then why does the universe give nothing but a dusty answer?

The fact that intelligent life in this universe is pretty damn rare is compelling evidence that ET must be carbon-based.

 

intelligent life on our own planet can be hard to find sometimes...

 

Only if a mirror is hard to find

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I cannot help but agreeing with that. Still, I believe we shouldn't completely run out the fact that there might be other kinds of life out there. I mean... it is all about best and worst case scenarios. Even the Drake equation use them.

Maybe there aren't now, but there might be in the future or there were in the past? Life happens in a blink of an eye for an observer with huge life-span. Consider there is a "god" outside our universe. He will perceive us as very tiny people. Chances are that he won't even get to know us, since the universe is so huge and we are so little! And since hi life-pan is much bigger then ours, he will have a lot of difficulty find us in the right time, considering the life-span of our civilization. In other words, if life is really rare, chances are that we won't be able to communicate. And that is covered by the Drake equation. What is not covered by that equation is the fact that there might be other forms of life, and that can make life much more likely to occur. Still, as we get to know the universe more clearly, particularly with our new techniques for finding extrasolar planets, the variables in the Drake equation keep changing, and they look more and more likely to support life a something eiter normal or even abundant in our universe (keep in mind that even if you consider 1 civilization in every solar sytem, that is still consider abundant given the absolute size of the universe compared to the relative size of a civilization's territory).

Well, a sample population of one will give us a HUGE margin of error... which means that by no means we should settle down with the amount of data that we have. But I believe that the sample population shold be the number of solar systems similar to ours. Then we can calculte the probability that a civiliation like ours might exist...

Because we can't see close enough yet. We can even find earth-like planet (they are being proven to be more and more common), but we can't still see what is going on on the surface of those planets, can we?

Whoa! You are soooooo narcisistic...

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Just teasing ya

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I beleive that life is very abundent in the universe. But has anyone stopped for a second and thought...wait maybe we were the first to evolve? Life could take millions of years to evolve to our status of intelligent beings. Also I saw something on the discovery channel I thought was interesting, they found some kind of life near a active volcano in some ocean that no sunlight got to. It was a small eco system that consisted of some kind of plant that got its energy from the volcano and some organism that consumed the other. Granted they were small but they were also probably created by themselves away from the surface influences meaning that life was caused 2 seperate ways on earth. The first way was through solar energy, and the second was through geothermic activity. Could it be possible that a moon of some planet in our own solar system with water and volcanoes have basic forms of life like the life at the bottom of our own oceans? Could pluto have life below its icy surfaces? My guess is that all basic life is carbon based because of the simplicity of the atom. Notice that all the esential elements Hydrogen, Carbon, Oxygen, Nitrogen, etc. are all relatively low on the periodic table of elements? I think I've rambled on too much.....

 

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Well TS, the issue with the balloon-people of Jupiter and the rock-dwarves of Venus is that they aren't there. You argue that they might once have been there before, and that's fine. But look at Earth. Let's say that some alien species inspects this solar system and there's an ice-age on Earth so there is no human civilization. There would still be life. If there were life on some other planet, that leaves the promise that intelligent life was once there. Yet, there is no Marsian biosphere. Even in the middle of an ice-age, there would be an Earthen biosphere. And even if an asteroid exterminates all life on Earth, you can't exterminate the microbacterial biospheres, even if you blew up the planet. The situation the human race finds itself in is that not only are there no alien cities, but no alien transmissions, no alien biosphere, no alien fossils, no alien bacteria even. The case that non-carbon based life can exist is harder to make if there is no evidence for it. What we know is that carbon-based life can exist, which is more than can be said for more exotic exobiologies.

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Just pointing out that Man --that I-- am intelligent. Pride is a virtue, you know. That's a bit of philosophy that makes me sad that the modern custom is to separate philosophy from physics.

:lol: Yes my friend, this *has* occurred to other people. You are not the first.

The universe is around 16 billion years old. They say the Earth is around 4.5 billion years old. Thus --using our flawed statistical sample of 1

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--we can say that it takes 4.5 billion years for intelligent life to evolve. Being the universe is four times that old, the mathematics lean toward the opinion that we are *not* the first.

 

CobaltSunrise,
i don't think that you can assume that life began and then evolved from the moment the universe came into existance. It took a fair amount of time for the first stars to form, it took more time for them to create the heavier elements required for life. So all though I agree that it is very possible that life began elsewhere in the universe before it did on earth, you can not say that it had 16 billion years to do so.

 

Chances are that that is not the case. Our solar system alone has about 4.5 billion years in the past. Our civilization is about 300 mliion years old, if I'm not mistaken. If you divide them, you get that our solar system is 15 times older then our civilization. So you can see that a civilization could have evolved a long time ago, died, and then ours could have born. There's enough time for a lot. But it is possible that we will last a much longer time, specially if we "conquer" other planets (and hopefully get out of this solar system, cause the sun will soon or later become an RR Lyra.

Yeah... I heard that before. I also heard there is some connection between bacteria that live in volcanoes and "breathe" sulphur, with detergents. I don't remember very well, but it was something like that. Also, there are many kinds of bacteria that use other sources of energy, other then sunlight and oxygen. Some, rather smelly ones...

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I wonder why they didn't evolve...

Sure. Europa is also a great candidate...
I wonder if there is intelligent life in Europa. I'm sure there isn't in Britan...

Why not Lithium, then? Besides, I would say that it is much more likely to see organisms based on those elements because of their relative abundance, compared to other higher elements such as iron, and above (which are only created in the explosion of huge supermassive red giants, and represent only about 1% of all its mass).

Well, thank you...

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Wait, wait. I "biosphere" is defined by a place that contains life. If there is no life, there is no "biosphere". Even if there is no "biosphere" in Mars today, there might have been or there might be one day...

Huuuuh.... maybe yes, on the latest one...

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We can only search for evidence in one grain in the whole Sahara desert. That's how good we are right now. But it is getting better, anyways....

Yeah, I know. We should have philosophy in High School....

 

Sure I can, I just have to correct the number. 16 billion is a starting point. But not just a starting point, but the point from which you *must* start. The issue then becomes "what corrections are reasonable?" I mean, our Sun went main-sequence ~11.5 billion years after zero hour. Or something like that, I would need to review stellar evolution, but remember it's a pretty rough number anyway. So! How long do you think it took for the *first* stars to form? A few nanoseconds, a billion years? But ah, the existence of *any* stars that are older than our sun prove the point: ET may be orbiting those stars. Whether our sun is a member of the First Generation of stars or not, the existence of other main-sequence stars proves my point well enough. I mean, both Toliman stars are main-sequence and ~1.5 billion years older than our sun; intelligent life had enough time to be born, live, suffer, and die around both those stars while life on Earth was nothing more than protozoa. And that's as close as two intelligent species get to meeting each other in this universe.