Freethought & Rationalism Archive

Doubting Didymus · 09-26-2002, 10:26 PM

Quote:

Originally posted by Jesse:
presumably single-celled organisms rather than multicellular ones.

Unless the life came from earth, There is no guarantee that the life would even be 'cellular' as we know it. It could be anything as long as it replicates.

Particularly unlikely is the possibility that whatever cell-thing might be found there looks like a eukaryote.

Jesse · 09-26-2002, 10:29 PM

Jeremy Pallant:
Agreed. The problem with xenobiology is that it is biased towards carbon based life forms. Did you read Robert L. Forward's Dragon's Egg? A fascinating "hard science" approach to alternate forms of life.

I do think that to have anything that could reasonably be called "life" you need some sort of complex, stable microstructure to play a role analogous to DNA and/or proteins. If you're interested in organisms made up of atoms, this pretty much limits you to carbon-based or possibly silicon-based life. I haven't read Forward's book, but I think he was speculating that on the surface of a neutron star you might find groups of protons and neutrons bound together in more complex ways than in the nuclei of atoms, so that these could play the role of "molecules." Maybe in some other exotic conditions other groups of particles (quarks?) could bind together in stable ways. Either way, it seems clear to me that life can't form anywhere or be made out of anything.

Jesse · 09-26-2002, 10:33 PM

Doubting Didymus:
Unless the life came from earth, There is no guarantee that the life would even be 'cellular' as we know it. It could be anything as long as it replicates.

Crystals and fires replicate, but they are not alive. I think you need the idea of inheritance, probably metabolism as well (to stave off entropy), and it's hard to see how you could get that without complex molecules (carbon-based or silicon-based) of some sort.

Doubting Didymus:
Particularly unlikely is the possibility that whatever cell-thing might be found there looks like a eukaryote.

Not like a eukaryote, but quite possibly some network of complex molecules enclosed by a membrane to keep them all in one place.

[ September 26, 2002: Message edited by: Jesse ]

Answerer · 09-27-2002, 01:49 AM

Quote:

Originally posted by Jesse:
Answerer:

According to the article, no one is suggesting that life exists on Venus's surface. In fact the surface is so hot that it might be that no stable complex molecules could exist there, making life impossible (my understanding is that carbon and silicon are the only elements which form really complex molecules--it's possible that silicon-based life could exist at higher temperatures than carbon-based life, I'm not sure). In any case, what the article suggests is that life may exist in Venus' cooler upper atmosphere, presumably single-celled organisms rather than multicellular ones.

Oh really, sound a bit disappointing as I'm really curious about the appearance and charactistic of silicon-based life.

Jesse · 09-27-2002, 02:12 AM

Here's a page that talks about the possibility of silicon-based life:

<a href="http://www.angelfire.com/on2/daviddarling/siliconlife.htm" target="_blank">http://www.angelfire.com/on2/daviddarling/siliconlife.htm</a>

Apparently the prospects for silicon-based life are pretty bad though--something to do with the way it reacts with oxygen, and the lack of silicon-based molecules that come in left- and right-handed forms like enzymes.

The website this came from, <a href="http://www.angelfire.com/on2/daviddarling/ETEmain.htm" target="_blank">The Astrobiology Encyclopedia</a>, is pretty neat...<a href="http://www.angelfire.com/on2/daviddarling/neutronstarlife.htm" target="_blank">this</a> page mentions the possibility of life on a neutron star which Jeremy Pallant brought up. And here's something on <a href="http://www.angelfire.com/on2/daviddarling/ammonialife.htm" target="_blank">ammonia-based life</a>, which I'd never heard of (this kind of life would still be carbon-based, but with ammonia playing the solvent role that water plays for life on our planet).

Coragyps · 09-27-2002, 05:54 AM

Quote:

What is the current status of THE Mars rock?

I read an article recently (and can't find it today - maybe in PNAS?) that listed five characteristics of the magnetite grains that were in the Allan Hills Martian meteorite that point toward a biological origin - their shape, they occur in chains,... etc. It was by McKay, et al., who are the "true believers" in Mars bugs; I don't discount it just for that, though. I'll look some more, and post a url if I find it.

Hot damn, I'm quick!
Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 5, 2164-2169, February 27, 2001

Find it <a href="http://www.pnas.org/search.dtl" target="_blank">here</a>. (The article's url would run over the page width here.)

[ September 27, 2002: Message edited by: Coragyps ]

Skydancer · 09-27-2002, 10:30 AM

Quote:

Originally posted by Jesse:
Here's a page that talks about the possibility of silicon-based life:

<a href="http://www.angelfire.com/on2/daviddarling/siliconlife.htm" target="_blank">http://www.angelfire.com/on2/daviddarling/siliconlife.htm</a>

Apparently the prospects for silicon-based life are pretty bad though--something to do with the way it reacts with oxygen, and the lack of silicon-based molecules that come in left- and right-handed forms like enzymes.

The website this came from, <a href="http://www.angelfire.com/on2/daviddarling/ETEmain.htm" target="_blank">The Astrobiology Encyclopedia</a>, is pretty neat...<a href="http://www.angelfire.com/on2/daviddarling/neutronstarlife.htm" target="_blank">this</a> page mentions the possibility of life on a neutron star which Jeremy Pallant brought up. And here's something on <a href="http://www.angelfire.com/on2/daviddarling/ammonialife.htm" target="_blank">ammonia-based life</a>, which I'd never heard of (this kind of life would still be carbon-based, but with ammonia playing the solvent role that water plays for life on our planet).

I'm not so sure I'd count out these possibilities so easily. Ammonia-based life might work out under conditions too cold for liquid water - the weaker intermolecular forces compensated by the slower motion of colder matter. Silicon is more problematic - the temperatures would have to be much higher to make things work, and to get an energy flow you might need creatures living at the surface of a lava pool. Limited habitat.

Jesse · 09-27-2002, 06:15 PM

Skydancer:
Silicon is more problematic - the temperatures would have to be much higher to make things work, and to get an energy flow you might need creatures living at the surface of a lava pool. Limited habitat.

What's your opinion on the other problems the page mentioned for silicon-based life? Specifically:

Quote:

Conceivably, some strange life-forms might be built from silicone-like substances were it not for an apparently fatal flaw in silicon's biological credentials. This is its powerful affinity for oxygen. When carbon is oxidized during the respiratory process of a terrestrial organism (see respiration), it becomes the gas carbon dioxide - a waste material that is easy for a creature to remove from its body. The oxidation of silicon, however, yields a solid because, immediately upon formation, silicon dioxide organizes itself into a lattice in which each silicon atom is surrounded by four oxygens. Disposing of such a substance would pose a major respiratory challenge.

Life-forms must also be able to collect, store, and utilize energy from their environment. In carbon-based biota, the basic energy storage compounds are carbohydrates in which the carbon atoms are linked by single bonds into a chain. A carbohydrate is oxidized to release energy (and the waste products water and carbon dioxide) in a series of controlled steps using enzymes. These enzymes are large, complex molecules (see proteins) which catalyze specific reactions because of their shape and "handedness." A feature of carbon chemistry is that many of its compounds can take right and left forms, and it is this handedness, or chirality, that gives enzymes their ability to recognize and regulate a huge variety of processes in the body. Silicon's failure to give rise to many compounds that display handedness makes it hard to see how it could serve as the basis for the many interconnected chains of reactions needed to support life.

The absence of silicon-based biology, or even silicon-based prebiotic chemicals, is also suggested by astronomical evidence. Wherever astronomers have looked - in meteorites, in comets, in the atmospheres of the giant planets, in the interstellar medium, and in the outer layers of cool stars - they have found molecules of oxidized silicon (silicon dioxide and silicates) but no substances such as silanes or silicones which might be the precursors of a silicon biochemistry.

Answerer · 09-27-2002, 09:19 PM

Thanks for the link, Jesse. Anyway, are there only two possible kinds of lifeform, silicon and carbon based or is there more?

WalrusGumBoot · 09-27-2002, 10:30 PM

Over the years I have observed that most, if not all, atheists shift the burden of proof of the existance of a god on the theist. Yet, at the same time, they are avid in embracing theories that are at best, speculative. Like this one about bacteria floating around in the atmosphere of Venus.

It's not to say it can't be true, but time and time again these speculations are shown to be false. The Mars rock, for example, was all over the newspapers, magazines, etc. as the discovery of all time. Now that has flopped, it's bacteria on Venus.

I'm just playing devils advocate here, but is this not the same reaction to speculation that creationionists are ridiculed of? There is no proof of any life anywhere than Earth, period, to date. Maybe NASA will use this to get government funding for a Venus mission like they did for Mars. Maybe this is all about money and job security for the space exploration industry.

Masters of critical thinking, it's time to apply it here to this latest theory, even if it is something that coincides with your world view.

[ September 27, 2002: Message edited by: WalrusGumBoot ]

09-26-2002, 10:33 PM	#23
Jesse Moderator - Science Discussions Join Date: Feb 2001 Location: Providence, RI, USA Posts: 9,908	Doubting Didymus: Unless the life came from earth, There is no guarantee that the life would even be 'cellular' as we know it. It could be anything as long as it replicates. Crystals and fires replicate, but they are not alive. I think you need the idea of inheritance, probably metabolism as well (to stave off entropy), and it's hard to see how you could get that without complex molecules (carbon-based or silicon-based) of some sort. Doubting Didymus: Particularly unlikely is the possibility that whatever cell-thing might be found there looks like a eukaryote. Not like a eukaryote, but quite possibly some network of complex molecules enclosed by a membrane to keep them all in one place. [ September 26, 2002: Message edited by: Jesse ]</p>

09-27-2002, 10:30 PM	#30
WalrusGumBoot Junior Member Join Date: Jul 2001 Location: Hempstead, Texas Posts: 20	Over the years I have observed that most, if not all, atheists shift the burden of proof of the existance of a god on the theist. Yet, at the same time, they are avid in embracing theories that are at best, speculative. Like this one about bacteria floating around in the atmosphere of Venus. It's not to say it can't be true, but time and time again these speculations are shown to be false. The Mars rock, for example, was all over the newspapers, magazines, etc. as the discovery of all time. Now that has flopped, it's bacteria on Venus. I'm just playing devils advocate here, but is this not the same reaction to speculation that creationionists are ridiculed of? There is no proof of any life anywhere than Earth, period, to date. Maybe NASA will use this to get government funding for a Venus mission like they did for Mars. Maybe this is all about money and job security for the space exploration industry. Masters of critical thinking, it's time to apply it here to this latest theory, even if it is something that coincides with your world view. [ September 27, 2002: Message edited by: WalrusGumBoot ]</p>

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09-26-2002, 10:29 PM	#22
Jesse Moderator - Science Discussions Join Date: Feb 2001 Location: Providence, RI, USA Posts: 9,908	Jeremy Pallant: Agreed. The problem with xenobiology is that it is biased towards carbon based life forms. Did you read Robert L. Forward's Dragon's Egg? A fascinating "hard science" approach to alternate forms of life. I do think that to have anything that could reasonably be called "life" you need some sort of complex, stable microstructure to play a role analogous to DNA and/or proteins. If you're interested in organisms made up of atoms, this pretty much limits you to carbon-based or possibly silicon-based life. I haven't read Forward's book, but I think he was speculating that on the surface of a neutron star you might find groups of protons and neutrons bound together in more complex ways than in the nuclei of atoms, so that these could play the role of "molecules." Maybe in some other exotic conditions other groups of particles (quarks?) could bind together in stable ways. Either way, it seems clear to me that life can't form anywhere or be made out of anything.

09-27-2002, 02:12 AM	#25
Jesse Moderator - Science Discussions Join Date: Feb 2001 Location: Providence, RI, USA Posts: 9,908	Here's a page that talks about the possibility of silicon-based life: <a href="http://www.angelfire.com/on2/daviddarling/siliconlife.htm" target="_blank">http://www.angelfire.com/on2/daviddarling/siliconlife.htm</a> Apparently the prospects for silicon-based life are pretty bad though--something to do with the way it reacts with oxygen, and the lack of silicon-based molecules that come in left- and right-handed forms like enzymes. The website this came from, <a href="http://www.angelfire.com/on2/daviddarling/ETEmain.htm" target="_blank">The Astrobiology Encyclopedia</a>, is pretty neat...<a href="http://www.angelfire.com/on2/daviddarling/neutronstarlife.htm" target="_blank">this</a> page mentions the possibility of life on a neutron star which Jeremy Pallant brought up. And here's something on <a href="http://www.angelfire.com/on2/daviddarling/ammonialife.htm" target="_blank">ammonia-based life</a>, which I'd never heard of (this kind of life would still be carbon-based, but with ammonia playing the solvent role that water plays for life on our planet).

09-27-2002, 09:19 PM	#29
Answerer Veteran Member Join Date: Feb 2002 Location: Singapore Posts: 3,956	Thanks for the link, Jesse. Anyway, are there only two possible kinds of lifeform, silicon and carbon based or is there more?

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