PDA

View Full Version : Carbon Based?



rahuldandekar
2004-May-25, 06:22 AM
Why do we all think that aliens are carbon based? Can't they be Silicon based, or even compuond based. Conditions would exist on their planet to permit existence of such life-forms.
Anythings possible. We shouldn't be baised towards carbon.

GOURDHEAD
2004-May-25, 01:14 PM
Physics, chemistry, and biology favor carbon based life. We have no reason to believe that any other combination of elements not centered on carbon can achieve spontaneous generation and evolve to sentient complexity. In competition with carbon based critters each will lose to the greater stability of the carbon based critters.

Our bias is reasonable.

SkyBoard
2004-May-25, 03:00 PM
On Titan,there's a lot of nitrogen and ammonium...so don't you think there would be nitrogen- or ammonium-based life there?

GOURDHEAD
2004-May-25, 03:34 PM
On Titan,there's a lot of nitrogen and ammonium...so don't you think there would be nitrogen- or ammonium-based life there?

Nope. More complex molecules are needed.

StarLab
2004-May-25, 03:38 PM
Nope. More complex molecules are needed.
Geez, Gourdy! Earthly DNA consisted of A G C and T. It was that simple. Don't you think that in another environmnet with different conditions from our own, that life may just yet be possible in some other different manner?

GOURDHEAD
2004-May-25, 03:46 PM
Don't you think that in another environmnet with different conditions from our own, that life may just yet be possible in some other different manner?

Yes, but carbon based. Maybe different at the amino acid and protein level, different chirality but equivalent complexity (RNA,DNA, etc.,) and carbon based.

John L
2004-May-25, 07:35 PM
The reason we are carbon based and that biologists feel it is the best, if not the only, method of creating complex biological life is because carbon can have up to four other atoms form molcules with a single carbon atom. Carbon has four empty slots in it outer electron shell that can be filled and this allows for some very complex chemistry to occur. Some have speculated that since silicon also has four open slots in its outer electron shell that maybe it could also from a basis for complex biological life, but we've found no examples of it, or any possible precursor chemicals such as silcon based amino acid type compounds that could form the basis of such a life form.

Pandora
2004-May-26, 12:13 AM
Most likely we are unique, and if any other life forms can exist elsewhere in the Universe, it will be us.

rahuldandekar
2004-May-28, 05:44 AM
What if silicon based life can exist elsewhere because the conditions are just right for silicon to form long-lasting polymers ? You know, on our planet, the conditions are also just right.
It's possible.

StarLab
2004-May-29, 12:24 AM
What if silicon based life can exist elsewhere because the conditions are just right for silicon to form long-lasting polymers ? You know, on our planet, the conditions are also just right.
It's possible.
I think It's already happenning...Computers. :ph34r:

rahuldandekar
2004-May-30, 11:27 AM
Yes, but computers are not spontaneous life. We are searching for life which has evolved on its own, not with help from other life.

Spacemad
2004-May-30, 11:49 AM
:) In one of Isaac Asimov´s books he tells how an alien civilization discovers the archaeological remains of an even earlier galactic civilization that had disappeared thousands of years earlier. In their investigations one particular archaeologist - who´s considered an outcast even in their society - discovers a planet of robots who were left more or less to their own devices as a sociological experiment by the super advanced but extinct civilization. This planet of robots had been forgotten for millions of years but this archaeologist discovers its whereabouts & makes a couple of trips there. The end of the story comes when he is discovered & his (forbidden) activities are questioned & he defends himself by saying that his activities had been discovered by the robots & that they had the right to live & they had in fact dismantled his own spacecraft & had discovered FTL & were about to leave their solar system & explore the galaxy. We then discover on the last page of the book that the planet of robots was in fact the Earth & the "Robots" were humans!! :P

So who knows if we appeared without outside intervention!!!! :P :D :lol:

rahuldandekar
2004-May-30, 12:03 PM
I liked that story. But our biologists are sure that we came into existence spontaneously. I, too belive it, because we have created amino acids in the lab by simulating conditions on the early earth.

Deep_Eye
2004-Jun-01, 06:01 PM
Carbon is usually the best because it's electron field is perfectly half full. (4 out of 8 electrons) Because of that, it bonds readily with itself. Some of the strongest materials on the planet, such as diamonds, and corundum are based from carbon.

abyssalroamer
2004-Jun-01, 10:47 PM
Corundum isn't a carbon-based mineral.

Deep_Eye
2004-Jun-01, 10:50 PM
It isn't? Oops..sorry. I know coal, graphite, and diamonds are though. Coal can be turned into graphite, and graphite into diamond (by metamorphism-intense heat and pressure)

John L
2004-Jun-02, 03:56 PM
Originally posted by abyssalroamer@Jun 1 2004, 05:47 PM
Corundum isn't a carbon-based mineral.
Corundum is aluminum oxide.

Deep_Eye
2004-Jun-02, 04:06 PM
Jeez man, have you like memorized all the main minerals and their components or something?

John L
2004-Jun-07, 04:45 PM
Originally posted by Deep_Eye@Jun 2 2004, 11:06 AM
Jeez man, have you like memorized all the main minerals and their components or something?
I Googled the word and it came up. Google can tell you anything! B) Ask it "How many grains in an ounce?" and it will come up with the conversion factor. It'll do all sorts of things if you just ask it. :D

And I don't work for them.

BlackTearsofapril
2004-Jun-14, 09:20 PM
Originally posted by Spacemad@May 30 2004, 11:49 AM
We then discover on the last page of the book that the planet of robots was in fact the Earth & the "Robots" were humans!! :P

So who knows if we appeared without outside intervention!!!! :P :D :lol:


Thats what I think we are. An experement. They took neanderthals, and geneticly mutated them, and created us, and then put us here to see what we'd do, and how we'd flourish in our surroundings. I bet they also have this synthesised in a lab of some sort, and we destroyed ourself and the planet.

rahuldandekar
2004-Jun-17, 10:23 AM
We could just have evolved from them you know? I don't think that we were the results of an experiment.

Tim Thompson
2004-Jun-18, 01:47 AM
Originally posted by rahuldandekar@May 25 2004, 06:22 AM
Why do we all think that aliens are carbon based? Can't they be Silicon based, or even compound based? Conditions would exist on their planet to permit existence of such life-forms. Anything's possible. We shouldn't be baised towards carbon.

"Anything" is not possible. Only those things permitted by the laws of physics are possible, the only caveat being that we have an incomplete knowledge of what those laws are. Life, as we understand it, is not posible based on silicon.

The reason for this is that, while silicon (http://www.webelements.com/webelements/elements/text/Si/key.html) (Si) has 4 bonding electrons available, like carbon (http://www.webelements.com/webelements/elements/text/C/key.html) ( C ), Si is a bigger atom; it makes longer & weaker bonds. One result of this is that Si only makes single bonds, while C will double bond. So, for instance CO2 is a closed shell molecule, because the C has double bonded to each of the O, whereas SiO2 has only two single Si-O bonds, and still has two electrons available to bond. So the Si electrons aren't used up until you get SiO4, but since the bonds are single, SiO4 has 4 loose electrons looking for bonds, one for each O atom. The bottom line is that Si forms crystals with O and does nothing greatly interesting with H. On the other hand, C forms a gas with O (CO or CO2), and creates a suite of noncrystalline molecules that are the basis of organic chemistry. If you create a definition of "life" that is sufficiently non-commital as to exactly what "life" is, then perhaps you can claim that Si based life can exist ("living crystals" that transmit information by moving crystal defects). But that is not "life as we know it".

And here's another point. Look at the relative abundances of the elements (http://www.astro.lsa.umich.edu/users/cowley/sad.html) (the plot is probably representative of the abundances in the present universe). Aside from the obvious H and He, the next most abundant elements in the universe are, in order, O, C & N (it might be easier to look at the table (http://www.astro.lsa.umich.edu/users/cowley/sadtab.html)). We already know that "CHON" is the basis for organic chemistry, and it's no coincidence that "CHON" are also the most abundant elements in the universe. The Si relative abundance is only about 1/10 that of C. So Si is both underabundant, and deficient in double bonds. It just does not work for "life as we know it".

We should be biased towards what we know. That is not to say that imaginative ideas are not welcome, but we learn best, I think, by extrapolating (even if by a long reach), from what we know. A simplistic look at Si, seeing that it has 4 loose electrons, animates that idea of Si based life. But we should not stop there and just say "anything's possible". We should look more closely and see what really is possible, and what that means.

eburacum45
2004-Jun-23, 03:44 PM
Carbon may be more common in the universe than silicon, but on Earth silicon is actually more abundant.

Having said that the form of life which has evolved on this planet is carbon based not silicon based, so obviously silicon based life has associated dificulties. Which if you compare carbon based organic chemistry with silicone chemistry, the advantages are obvious. For a start the oxide of carbon is a gas, the oxide of silicon is a rock.

Nevertheless I have imagined two fairly far-fetched types of silicon based life; one is a collection of self-organised rheolithic crystals in lavatube conditions; the other is descended from ancient self-evolving Von Neumann machines sent out millions of years ago by a possibly extinct alien race...
science fiction of course, but perhaps possible somwhere in the infinite universe...

suntrack
2004-Jun-26, 10:03 AM
CARBON IS UNVERSAL WASTE?



sunil deshpande

Pandora
2004-Jun-28, 01:53 AM
With so many extreme conditions existing on earth, if life were to have originated in any other form we surely would have found it. Other places in the universe studied so far are less hospitable. It's a wonder, too, why all life on this planet is traceable to one original DNA molecule. If anything else got a start, it didn't survive long enough to leave a mark.

GOURDHEAD
2004-Jun-28, 02:07 PM
Other places in the universe studied so far are less hospitable.


However true that may be, we have not studied any place other than earth with sufficient thoroughness to really know. Although "far less hospitable" several places in the solar system besides the large moons of the gas giants are not necessarily prohibitively hospitable. Both Mercury and the moon could be hosting microscopic life miles below their surfaces where acquifers may exist. Although less likely, Venus and the gas giants may harbor life in their atmospheres. We don't have enough data yet to really know. It's not the sort of thing you'd want to bet the lunch money on.

Weaselbunny
2004-Jun-28, 04:27 PM
I thought I heard something about them finding evidence of non carbon based life near geo thermal vents deep deep below the ocean, but I can't Google anything up. Maybe it was wishful thinking.

I don't know all the science but I would like to think that 'Our current understanding' is that it is not possible, but in an infinite universe with plenty still to learn... who knows!

Call me a dreamer if you like. :P

Tom2Mars
2004-Jun-29, 01:41 AM
Weaselbunny! Where You Been?

I did a google search using "tube worms geothermal vents and a bunch of stuff came up, including this at the top:Ocean Floor:Hot Springs... (http://pubs.usgs.gov/publications/text/exploring.html)

The tube worms do not rely upon photosynthesis for energy, but rather chemosynthesis (chemicals). This one article I looked at did not contain any reference to carbon in the list of chemicals that the tubeworms and their bateria buddies depend on, so until someone finds a different article, you could be correct. :unsure:

eburacum45
2004-Jun-29, 09:32 AM
No, these are ordinary carbon based lifeforms; they have the same type of body chemistry as the rest of life on Earth.

These deep sea organisms which cluster around 'black smoker' vents gain their energy from the internal heat of the Earth; chemoautotrophic bacteria use the chemical enrgy of the vents to support a food chain which is independent of the Sun's radiation. Such chemoautotrophy might be common on other planets in the universe; we just don't know.

Weaselbunny
2004-Jun-29, 11:22 AM
Hey Tom, been busy, but I've still been looking in on the threads from time to time.

I read the article, it could be what I was thinking about, but I seem to remember these odd creatures were surviving in a radioactive environment or something similar... again, maybe it was a vivid dream I had or maybe I picked it up somewhere but got my facts skewy, cos let's face it, if there was non-carbon based life on the planet, surely there'd be something on the net about it.

How's your space ship going Tom, still up for a race! :P

eburacum45
2004-Jun-29, 08:16 PM
There are extremophiles which are resistant to radiation as well; Deinococcus Radiodurans, which can survive life in the cooling system of a nuclear reactor;

they have specially hardened protein coats around their DNA to prevent shuffling during radiation damage.

But they too are carbon based life.

One day the anti-radiation strategy of these extremophiles will become part of the genetic armory of humanity also, thanks to inheritable genetic modification.

wstevenbrown
2004-Jul-06, 07:37 PM
Silly notion, but here it is anyhow. In the very early universe, before the "waste products" C, O, and N were excreted by supernovae, might life not have evolved in some other way? We make much of the fact that Carbon is the only suitable chemical basis, but there was a long era, after the creation of Population III stars, when no chemistry at all was possible, there being no chemicals. Helium forms no compounds, hydrogen only one, the diatomic molecule. The stars themselves were different-- with no metals to drive the carbon cycle and other catalytic cycles, they had to be more massive to burn at all, using the proton-proton reaction. The planets also would have evolved differently, with no dust to stick to, it's tricky getting gas to form planets at all! Still, I wonder if, on the smallest possible such planet superconductive He might not have self-organized and developed information storage and processing. The contradiction, of course, is that the heat of formation of the planet would forbid being cool enough to superconduct. Within the larger planets, tho, pressure and temperatures prevail that force H to behave like a metal. A very lonely metal. Very small amounts of Li and even smaller amounts of Be and B to party with, but they would have been segregated toward the core by their weight. Being the only active chemicals, theirs would be the only chemistry. (Borane, borane!) The dwarf stars of that era are still around, as the universe is not old enough for them to have evolved outside their stable range, and while their planets might not be capable of the preferred chemistry, they have had a very long time in which to do something. My point (see, I did remember) is that we know very little about the chemistry of light elements at extreme high pressure, and still less about the phase behavior. For example, there are now at least twelve allotropes of water ice (different crystal forms arising at different temp/press combinations). I'm not pressing any particular point of view here, just striking a blow against Carbon Chauvinism. (Isn't it funny how, when the only tool in your box is a hammer, everything gets compared to a nail?) Oh, yeah-- the same set of arguments apply to our local, more evolved gas planets J-S-U-N-P-.... Regards, Steve

Lomitus
2004-Jul-07, 04:32 AM
I know I'm a little late jumpin in here, but I think Carl Sagan covered this very nicely in "Cosmos". Yes silicone based life might be possible as well as other elements (maybe elements we have yet to discover), but carbon is plentiful in the universe and seems to be the most likely element to be used for life (err...so to speak). It's been a while since I saw that episode of Cosmos or read the book, but he covers it pretty well. On the other hand, I'm also rather biased...I really like the late Dr. Sagan's work :-) He had a unique way of putting a lot of this into perspective for those of us that aren't quite as scientifically inclined. He also would have been very proud of the work we're doing with the Mar's Rovers and with Cassini...shame he missed it.

What we may eventually find is that there is other kinds of life out there, such as silicone-based, but it might be -very- rare...it might exist, but not nearly as commonly as carbon-based.

I would like to add that just because a life form is carbon based, does not mean that it's going to look anything like us or anything we have on this planet. Life that evolves on other worlds (sentiant or not) will be adapted to that world and even on another "Earth-like" world, intelligent life could evolve much different from what we know. The diversity of life on our planet alone is astounding and if you multiply that by the possibility of other evolutions on other planets...perhaps even "billions and billions", carbon-based or not, the outcome could be truly mind-blowing!

Just my $.02
Bright Blessings All,
Jim

Floored_Music
2004-Jul-09, 10:37 AM
Originally posted by Tim Thompson@Jun 17 2004, 06:47 PM
We should be biased towards what we know. That is not to say that imaginative ideas are not welcome, but we learn best, I think, by extrapolating (even if by a long reach), from what we know.
Here, here! I cannot agree strongly enough. My personal pet peeve is to hear someone call something a "theory" without so much as a single attempt at theoretical discovery or basis on anything known to science. I dont know enough about chemistry to add to the specifics of this particular debate, but I do think the "anything is possible" approach to these kinds of discussions comes up all too often and only serves to diminish their real value.

Well said, indeed! Thank you. B)

Weaselbunny
2004-Jul-10, 03:32 PM
Here, here! I cannot agree strongly enough. My personal pet peeve is to hear someone call something a "theory" without so much as a single attempt at theoretical discovery or basis on anything known to science. I dont know enough about chemistry to add to the specifics of this particular debate, but I do think the "anything is possible" approach to these kinds of discussions comes up all too often and only serves to diminish their real value

Surely if there was 'a theoretical discovery' (I am presuming you mean proof) it would cease to be a theory and become fact.

And the suggestion that silicon based life may be possible is based on science (chemistry/physics) which I only loosely understand also. But still, scientific basis nonetheless.

As for 'anything is possible' responses... I'd rather be a dreamer and an optimist than an empiricist. B)

I know lots of people like tidy answers, but sometimes I think the messy ones can be more fun (that's probably why I'm a creative and not a scientist!) :P Don't rain on my parade man! :)