For the alternative theorists:

[Trippy]

http://www.news.harvard.edu/gazette/1996/09.12/CreatingLifeina.html

I have great confidence in an eventual recipe for cooking utility "stemcells" .

Your source predates the work that was done in 2007 after Miller died. They found some sealed viles from his original experiments and ran them through some modern equipment which is decidedly more sensitive. They found 22 amino acids and 5 amines, substantialy more than Miller originally reported.

Source

 

[Trippy]

To adopt the theory of "meteorite seeding" is to believe the Earth itself could not have provided whatever it is meteorites are supposed to have brought. It is as superfluous as "alien seeding" theory, and if there is a reason to believe one, than that is the same reason to include the other.

Complete bullshit. We have direct evidence that unequivocally demonstrates that carbonaceous chondrites not only carry amino acids but carry them as a heterochiral mixture enriched in the same enatiomers that life has evolved to use.

Alien intervention, on the other hand, has as much evidence for it as divine intervention. What you're presenting is a logical fallacy.

I do not see any good reason to involve meteorites and I do not see any good reason to involve aliens, equally so.

:Sigh:
Meteorites involve themselves.

Look, earth's water was delivered by comets.
Those same comets produce carbonaceous chondrite meteorites.
Those same carbonaceous chondrite meteorites carry evidence of water alteration and display a heterochiral mixture of amino acids.

Oh, and we have experimental evidence suggesting that amino acids contained within comets would survive the impact.

I don't even know why I'm arguing about this with you anymore, you're wasting my time.

I made two points.

I suggested that on the one hand meteorites might have seeded the earth with a heterochiral mixture.

And then suggest that on the other hand, the evidence from meteorites indicates that partial recrystalization maybe sufficient to produce a sufficiently heterochiral mixture to produce homochiral chemistry.

I didn't argue that meteorites were neccessary, or somehow special, or what ever you think is going on. The only person that infered that was you.

Stop wasting my time with your misunderstanding.

 

[paddoboy]

Complete bullshit. We have direct evidence that unequivocally demonstrates that carbonaceous chondrites not only carry amino acids but carry them as a heterochiral mixture enriched in the same enatiomers that life has evolved to use.

Being a nice bloke, I didn't want to put it as strong as that.
I believe in treating these newbies with kid gloves for a while.

 

[humbleteleskop]

Correct. And that's the problem. 'Nature' produces racemic mixtures, however, the life we observe around us is homochiral.

Is it a mixture of identical or different molecules that is racemic? Is it maybe that some specific molecules are chiral one way and other molecules chiral the other way?

Chemical reactions produce racemic mixtures that contain equal amounts of both enantiomers. racemic mixtures, when reacted, produce more racemic mixtures. In order to produce homochirality, as observed in life, from a racemic mixture you need some kind of refractory method to enrich one or deplete the other.

So all meteorites are found out to carry left-handed amino acids? And you believe there were so many meteorites that they saturated the Earth with these left-handed amino acids so it was a matter of probability the life would begin to utilize them rather than right-handed ones?

There's no magic involved. Chemistry doesn't somehow 'know' to react L-enantiomers with L-enantiomers and D-enantiomers with D-enantiomers. L-enantiomers react just as readily with D-enantiomers as they do other L-enantiomers (give or take the occasional steric consideration). The most parsimonious explanation is that life is homochiral because the mixture of amino acids life evolved from was homochiral or maybe heterochiral.

Are you saying both chiral versions of any particular molecule are always equally stable?

 

[Write4U]

Look, earth's water was delivered by comets.

Yes and frozen at that, preserving anything that was present at the time the ice formed.

The term "meteoric debris" from a billion years of collision and absorbtion of chemicals from all areas of the universe, does not sound so trivial anymore as a source for a random "seeding" process. I would not rule out Panspermia in addition to Abiogenesis. All the pieces of the puzzle are present. We just haven't found the exact way the pieces fit together and under what circumstances. But we shall, in time.

 

[humbleteleskop]

We have direct evidence that unequivocally demonstrates that carbonaceous chondrites not only carry amino acids but carry them as a heterochiral mixture enriched in the same enatiomers that life has evolved to use.

That only makes meteorites more likely than aliens, and I don't care. I'm saying the reason to propose anything external to Earth is superfluous to begin with.

Look, earth's water was delivered by comets.

First time I hear that. Reference?

Those same carbonaceous chondrite meteorites carry evidence of water alteration and display a heterochiral mixture of amino acids.

I suggested that on the one hand meteorites might have seeded the earth with a heterochiral mixture.

There were, and there would be, plenty of heterochiral amino acids without meteorites.

And then suggest that on the other hand, the evidence from meteorites indicates that partial recrystalization maybe sufficient to produce a sufficiently heterochiral mixture to produce homochiral chemistry.

Sufficiently heterochiral? How much is that: 55%, 70%, 90%? So then life should have proportionally utilized either one deepening on the quantity ratio, but the life still almost always "chose" one side over the other, so the question remains. Doesn't it?

And, are you saying this heterochiral mixture was predominant all over the whole planet? Was it happening all over throughout many years, or are you suggesting it happened like in a single event at some specific place and then the rest of life evolved from there?

 

[paddoboy]

That only makes meteorites more likely than aliens, and I don't care. I'm saying the reason to propose anything external to Earth is superfluous to begin with.

You don't care??? Excuse me while I have a big belly laugh. :bravo:
What a copout...again!

First time I hear that. Reference?

A reasonably common theory for anyone truly interested in science and cosmology
http://www.space.com/13185-comets-water-earth-oceans-source.html

There were, and there would be, plenty of heterochiral amino acids without meteorites.

As explained earlier, both are theoretically possible.
No one denies that except you.

 

[Write4U]

That only makes meteorites more likely than aliens, and I don't care. I'm saying the reason to propose anything external to Earth is superfluous to begin with.

Then all are in agreement on that, finally!!!!!! It makes no difference when or where, the only logical "assumption" we can make is that life emerged from non-living matter at sometime during the evolution of the universe, because in the physical sciences only matter can be alive. However the "potential for life" was created during the BB.

 

[Motor Daddy]

The term "life" is referring to a system such as a human, or a goat (not the GTO type of goat, a regular goat, but a GTO would work too as an example of a system. ) A system is not an object, it is a system, a composition of objects that have inputs and outputs.

The term "matter" is referring to a system such as a solar system. There is no ultimate "object" that is not a system.

So life and matter are systems, like a solar system...

 

[exchemist]

That only makes meteorites more likely than aliens, and I don't care. I'm saying the reason to propose anything external to Earth is superfluous to begin with.




First time I hear that. Reference?




There were, and there would be, plenty of heterochiral amino acids without meteorites.





Sufficiently heterochiral? How much is that: 55%, 70%, 90%? So then life should have proportionally utilized either one deepening on the quantity ratio, but the life still almost always "chose" one side over the other, so the question remains. Doesn't it?

And, are you saying this heterochiral mixture was predominant all over the whole planet? Was it happening all over throughout many years, or are you suggesting it happened like in a single event at some specific place and then the rest of life evolved from there?

Humbleteleskop, I'm not sure quite why you seem to be so hot under the collar about this. It seems to me all that is being said is that if mixtures that are not fully racemic have been found in extraterrestrial objects, it is at least suggestive of a possible extraterrestrial origin for some of these components in Earthly life. Surely nobody is saying it is certain, are they?

I imagine this finding leads logically to 3 possibilities: either (a) there is something about the chemistry of both Earth and extraterrestrial objects that militates in favour of chirality: if so then we need to identify what: or (b) the chirality of Earthly life indeed does derive from these extraterrestrial sources - which then pushes us back to the same question of what can have created the chiral preference in these objects; or c) it is an artifact due to contamination or something (even though I imagine this will have been the first thing people will have tried to check).

 

[humbleteleskop]

You don't care???

Yes, just as explained previously. I clearly said what I believe, post #1576: - "there was, and there still is to this day, plenty of diverse activities all around and inside the Earth to give rise not only to one, but perhaps many different pathways for abiogenesis and spontaneous emergence of life." And what I do not believe, also post #1576: - "I do not see any good reason to involve meteorites and I do not see any good reason to involve aliens, equally so."

A reasonably common theory for anyone truly interested in science and cosmology
http://www.space.com/13185-comets-water-earth-oceans-source.html

That there is water on meteorites is no any evidence they are responsible for any significant amount of water on the Earth. Why do you think water could not have been produced within the Earth itself?

As explained earlier, both are theoretically possible.
No one denies that except you.

I don't deny, I say meteorites are insignificant and irrelevant as abiogenesis would have surely happen without them.

 

[paddoboy]

Yes, just as explained previously. I clearly said what I believe, post #1576: - "there was, and there still is to this day, plenty of diverse activities all around and inside the Earth to give rise not only to one, but perhaps many different pathways for abiogenesis and spontaneous emergence of life." And what I do not believe, also post #1576: - "I do not see any good reason to involve meteorites and I do not see any good reason to involve aliens, equally so."

Again, we don't have hard evidence either way, except to say Abiogenesis and Evolution are near certain.
Again meteorites, comets are left over debris from the early solar system and were a great part of early Earth and its environment, and that most logically could have included Panspermia,
Whatever else you see or don't see, as good reason for your weird beliefs, is nether here nor there. :shrug:

That there is water on meteorites is no any evidence they are responsible for any significant amount of water on the Earth. Why do you think water could not have been produced within the Earth itself?

I don't dispute water may have been produced on and by Earth. I'm saying Earth was certainly bombarded my many many meteorites and comets of various sizes and that these contain plenty of water.
Therefor the theory of water from comets is a viable theory.

I don't deny, I say meteorites are insignificant and irrelevant as abiogenesis would have surely happen without them.

Maybe...I already said that too. But we don't know what lead to life on Earth in the first instant..
Good to see you at least support the near certainty of Abiogenesis and Evolution though, unlike leopold and dmoe.

 

[humbleteleskop]

Then all are in agreement on that, finally!!!!!! It makes no difference when or where, the only logical "assumption" we can make is that life emerged from non-living matter at sometime during the evolution of the universe, because in the physical sciences only matter can be alive. However the "potential for life" was created during the BB.

Two of us agree about everything, except one thing. You are willing to throw out aliens together with meteorites and I am not, even though I believe the Earth was more than sufficient to facilitate abiogenesis by itself.

You believe abiogenesis could have happened on many planets, right? So there is a possibility of some extraterrestrial species to have come here from some place else and played a significant part in abiogenesis and maybe also evolution. Yes? Isn't that exactly kind of thing humans would do if and when their race advances to such high technological level that those things would be possible, or maybe even necessary for survival? It's true, you know it. Given that stars have their expiry date, it's the only way for any civilization that managed to survive dying of their sun. So it's not completely arbitrary proposition, and however low, you have to admit the actually likelihood is more than zero.

 

[humbleteleskop]

Humbleteleskop, I'm not sure quite why you seem to be so hot under the collar about this. It seems to me all that is being said is that if mixtures that are not fully racemic have been found in extraterrestrial objects, it is at least suggestive of a possible extraterrestrial origin for some of these components in Earthly life. Surely nobody is saying it is certain, are they?

Because there are significant differences.

a.) abiogenesis was happening at many place over some extended periods of time
b.) abiogenesis happend at one place, only once, and all the life evolved from there

The difference is that the first one is inevitable consequence of initial conditions, while the second one is a consequence of limited probability. The first one is "natural", the second one is "miraculous". My problem with "meteorite seeding" theory is that it seems to suggest this "one time" miraculous event type of thing.

I imagine this finding leads logically to 3 possibilities: either (a) there is something about the chemistry of both Earth and extraterrestrial objects that militates in favour of chirality: if so then we need to identify what: or (b) the chirality of Earthly life indeed does derive from these extraterrestrial sources - which then pushes us back to the same question of what can have created the chiral preference in these objects; or c) it is an artifact due to contamination or something (even though I imagine this will have been the first thing people will have tried to check).

Yes, that's the other thing about "meteorite seeding" theory, it does not explain chirality problem as it was suggested it does. So what's the real answer? I think we should should first know if both chiral versions of any particular molecule are always equally stable, do you know the answer to that question?

 

[Write4U]

The problem is that apart from a few cave paintings pointing to the stars, to my knowledge, there is no evidence whatever for a visit by an advanced alien species, although it is entirely possible. I was grading the potential for an alien visit and that would still not solve the question of life emerging from non-life.

One thing is true, until we succeed in making a living organism from non living materials the question is wide open for delicious speculation...

 

[Trippy]

Is it a mixture of identical or different molecules that is racemic?

A racemic mixture is a mixture that has equal amounts of the dextrorotary and levorotary enantiomers. A mixture can have multiple optically active (chiral) substances in it and still be racemic.

Is it maybe that some specific molecules are chiral one way and other molecules chiral the other way?

No. Chirality is a form of symmetry. It is a reflection operation, and reflection is the only way to convert enantiomers.

Where R is the functional group denoting which amino acid it is.

They're like hands.

Hands are chiral. You can not make a left hand into a right hand with any combination of translation and rotation, it requires reflection.
Feet are chiral. You can not make a left foot into a right foot with any combination of translation and rotation, it requires reflection.
Because (under ordinary standards) left and right hands and feet occur in equal numbers, a roomfull of people are raecemic. It would take some sort of refactory operation, for example, amputation, to convert a room full of people into a homochiral mixture of people (they would probably object, and I doubt it would get ethics approval).

Wine glasses, on the other hand, are not chiral.

So all meteorites are found out to carry left-handed amino acids?

No. A particular class of meteorites has been observed to carry an excess of left handed amino acids. Carbonaceous chondrites[/quote]. All carbonaceous chondrites carry organic material. This organic material includes amines and amino acids.

And you believe there were so many meteorites that they saturated the Earth with these left-handed amino acids...

My understanding is that most of the water that the earth posesses was delivered to it by comets and carbonaceous chondrites (eg [url=http://www.psrd.hawaii.edu/CosmoSparks/July12/Earthwater-sources.html]source). I'm also of the understanding that carbonaceous chondrites, or at least some of them, are related to comets (eg here. So regardless of what might have been subsequently or previously generated in the earths atmosphere as a raecemic mixture, there exists an additional source which happe

so it was a matter of probability the life would begin to utilize them rather than right-handed ones?

More or less, yes.
If I take a room full of 40 people, and 20 of those people have had the left hand and left foot amputated, and the other 20 have had their right hand and right feet amputated. Then if I bring in a busload of 20 people with 15 people with the right hands and feet amputated, and 5 people with their left hands and feet amputate. The net result is that any random selection from this new room full of people is going to have an excess of left handed people.

Are you saying both chiral versions of any particular molecule are always equally stable?

Yes. Enantiomers have identical chemical properties, they generally have identical physical properties as well. My memory is a little hazy on the whole solubility thing, but then you've got eutectic mixtures and other kinds of craziness going on. But yes. Enantiomers are chemically identical. Threonine is an example of my point here.

 

[Trippy]

That only makes meteorites more likely than aliens, and I don't care. I'm saying the reason to propose anything external to Earth is superfluous to begin with.

And I'm saying you're wrong, on both counts.

First time I hear that. Reference?

Seriously?

There were, and there would be, plenty of heterochiral amino acids without meteorites.

The structure of this sentence suggests you have no idea what you're actually saying.

Sufficiently heterochiral? How much is that: 55%, 70%, 90%?

:Shrugs: However much it takes.

So then life should have proportionally utilized either one deepening on the quantity ratio, but the life still almost always "chose" one side over the other, so the question remains. Doesn't it?

Life didn't choose anything, and the only thing that any of this suggests is that if life using right handed amino acids ever evolved then life using left handed amino acids was able to outcompete it. Availability of resources is one method by which this might occur.

And, are you saying this heterochiral mixture was predominant all over the whole planet?

That depends. Do you think that life evolved the same way all over the world at the same time? Or do you think that the now dominant format of life evolved in a handful of places and spread outwards?

Was it happening all over throughout many years, or are you suggesting it happened like in a single event at some specific place and then the rest of life evolved from there?

I'm not speculating on anything of the sort.

 

[Trippy]

Humbleteleskop, I'm not sure quite why you seem to be so hot under the collar about this. It seems to me all that is being said is that if mixtures that are not fully racemic have been found in extraterrestrial objects, it is at least suggestive of a possible extraterrestrial origin for some of these components in Earthly life. Surely nobody is saying it is certain, are they?

Thankyou! (And paddoboy).

I imagine this finding leads logically to 3 possibilities: either (a) there is something about the chemistry of both Earth and extraterrestrial objects that militates in favour of chirality: if so then we need to identify what.

Quartz crystals, I seem to recall, have been forwarded as one possibility here. They're chiral. The observation is that if you start from a homochiral substrate or solvent then you wind up with homochiral product - consider Pasteur's experiment with Tartaric acid as an example.

or (b) the chirality of Earthly life indeed does derive from these extraterrestrial sources - which then pushes us back to the same question of what can have created the chiral preference in these objects;

There have been several possibilities advanced, the first to that spring to mind are it being linked to the handedness of the weak force, and it being because of preferential destruction by circularly polarized light from the same nearby supernova that generated the aluminium isotope anomalies.

or c) it is an artifact due to contamination or something (even though I imagine this will have been the first thing people will have tried to check).

The Allen Hills meteorites are generally regarded as being fairly pristine. One of the patterns that has been noticed is that the enantiomeric enrichment is well correlated with the degree of aqeuous alteration.

 

[humbleteleskop]

One thing is true, until we succeed in making a living organism from non living materials the question is wide open for delicious speculation...

I believe those replicating vesicles in Szostak's experiments qualify to be called alive, they fit the description.

http://molbio.mgh.harvard.edu/szostakweb/researchVesicles.html

1. Homeostasis
2. Organization
3. Metabolism
4. Growth
5. Adaptation
6. Response to stimuli
7. Reproduction

 

[Trippy]

That there is water on meteorites is no any evidence they are responsible for any significant amount of water on the Earth. Why do you think water could not have been produced within the Earth itself?

Because the frost line - the line in the solar system where water can exist as ice, lay between the orbits of Jupiter and Mars. That's why Jupiter is thought to have gotten so big, it was close enough to the sun that the solar nebula was dense enough for a large planet to form, however, far enough away from the sun that it was able to take in ice as well as silicates - with hydrated silicates being the primary source of earth's native water.

The hypothesis is supported by multiple lines of evidence, including isotopic evidence.