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Author | Topic: Excellent paper-peptide self assembly | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
Isn't the left-handed molecule simply named as the left-handed molecule because it is the first one discovered, and then the inherent mirror to that molecule around a given point would be the right-handed molecule? Otherwise, how would one decide, given a previously never-witnessed molecule, that it was left or right handed?
------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
And what evidence do you have that amino acids of different chiralities join readily?
------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
1) This doesn't cover how readily opposite chiralities bond - it just briefly mentions that it's possible. Of course it's possible - the issue here is how readily they will. You can even cause xenon to bond in the right conditions Did you not read my post? I stated "readily".
2) The body of the summary undercuts your position - it states that for opposite chiralities to bond, there would need to be a production process which creates a mix of chiral forms, and as a consequence, researchers are only concerned with the production process (i.e., it doesn't seem realistic that there would be a production process that would create such a mix) ------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
quote: My apologies, I misread your article summary as saying something to the opposite. However, you still have not answered part 1 - i.e., my initial question. Note that it is a question, not a statement, but I have yet to see a valid response to it. One would think that there is a difference in bonding affinities between different chiralities, because a common methods of separating racemic mixtures include seeding with a crystal of one enantiomer and chemical reaction with a chiral reactant. It would seem that once a hypercycle began with one chirality, that chirality would be locked in.
quote: Are you unfamiliar with the Murray and Murchison meteorites? Of course, that is just one possibility. I hope you're not playing a game of "God of the Gaps" here.
quote: Would you, perchance, happen to have the ratios of chiralities in the aforementioned meteorites on hand? I'm having trouble tracking it down. This topic always reminds me of a quote by Albert Einstein, when asked about why there are more electrons than positrons in the universe: "The electron got there first." ------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
Thanks for digging up the percentage on the Murchison meteorite. The Murray meteorite also had a non-racemic mixture, although I would imagine that the percentages were also not *too* high of a L/R ratio.
quote: As you'll notice from my post on this subject, however:
quote: You didn't address the key points of my posts (and I would be interested in your response). 1) The same point that I've brought up from the beginning that you haven't addressed: How readily enantioisomers react; I presented evidence that suggests that they don't react as readily. 2) How once a hypercycle starts with a certain set of amino acids, it is effectively "locked in". ------------------"Illuminant light, illuminate me." [This message has been edited by Rei, 11-02-2003]
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
quote: If your claim about that is due to inhibitory effects exhibited in racemic mixtures, you're ignoring the fact that, given a chiral "seed" or reactant - any sort of chemical, in fact, which favors one isomer over another - racemic mixtures can readily be separated. Do a search for the word "stereoselective" (or "enantioselective") and "synthesis" - I get 26,200 hits on google for the former, and 23,000 for the later - almost all papers and books on various reactions. Also, all of your posts argued in favor of my initial point: that reactants of different chiralities do not readily react with each other. That is the very claim that I made that started off this discussion here - check the history. Finally, you're still dodging #2: That once a hypercycle begins with a certain chirality, it is effectively "locked in". ------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
quote: /*Pretentious Code Brackets*/ Hmm, I'm not familiar with this line of argument before. What is it, the "Don't you think someone would have thought of it before?" argument? Can you actually add any substantive backing, or are you going to leave it at that?
quote: The process is known as "resolution" of the mixtures, and there's nothing secret about it; I'm surprised that you're even trying to debate about the topic without any sort of familiarity with how racemic mixtures are separated in the lab (to know how it applies to nature). The traditional method is the introduction of a chiral reactant or catylist (which need not be complex at all). Chiral reactants only react with one chiral form; the result is a diastereomer (look up the term yourself). The diastereomer and the desired chiral form are then separated via fractional crystallization (which itself can occasionally be used to separate chiral forms on its own, such as in racemic acid, an isomer of tartaric acid). How familiar are you with fractional crystallization, BTW? Everything keeps boiling down to the exact same point, DNAunion - my very first point: Different enatioisomers don't play well with each other; they much prefer to bond with their own types.
quote: It depends on what you're building. Clearly some chemicals have absolutely no problem with cross inhibition (such as quartz), despite racemic forms existing (quartz's lattice can spiral clockwise or counterclockwise (which effects the polarization of light), but rarely both in the same small area of a given crystal). It is an example of one of many cases where cross inhibition is limited due to the reduced "reactivity" of one "reactant" with another. Varying levels of inhibition are widely recognized in organic chemistry; for example, when studying a chiroselective peptide replicator, chemists at Skaggs found that "TLL autocatalytically accelerates its own production in reaction mixtures containing equimolar amounts of NL and EL (reaction 1; Fig. 3c), and adding TDD, TDL or TLD individually did not have any observable influence on the rate of TLL production. Indeed, reactions between NL and EL in the presence of equimolar amounts of all four templates, TLL, TDD, TDL and TDL (reaction 2), displayed a similar rate of product formation to that of the reaction where TLL was the only template present (Fig. 3c). These experiments suggest that TLL is the only active template involved in the ligation of EL and NL, and that all the other templates (enantiomer and diastereomers) act only as spectators during the formation of TLL (Fig. 3c).". Why on earth would you expect all cross-inhibition rates to be the same? Why would you expect no diastereomers? Please answer these questions before you continue.
quote: /*Pretentious Code Brackets*/ And you have yet to provide any evidence, despite being asked to multiple times. "Asserting" that someone is wrong without providing requested evidence merely makes you look inept at debating.
quote: /*Pretentious Code Brackets*/ So, then, my point stands in its original form, so I'll reiterate in boldface: Once a hypercycle begins with a particular chirality, that chirality is "locked in"..
quote: Still having fun with your cite? Unless by "external" they mean any sort of chiral reactant or catalyst (i.e., rather easy to come by), or unless by "if chiral reactants or catalysts are involved," they're not meaning homochiral (as would seem to be implied by the next line), then it's incorrect (I already cited an example with *zero* cross inhibition - I got tons of hits when searching, want more examples?). Or are you going to continue to harp on the fact that I misread it the first time you posted it (something that I acknowledged)? Again, I refer you back to the two things you need to answer in your next post: 1) Why would you expect all cross-inhibition rates to be the same?2) Why would you expect no diastereomer production (altering the isomer ratios)? ------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
My apologies; I was rather busy for a while, and forgot about this thread. First off, I stated that a *chiral* catalyst is used to separate them - but that means that a very small amount of imbalance in the catalyst will have dramatic effects in the overall isomer makeup of the solution.
If a small imbalance in an initial catalyst leads to a larger imbalance in the solution as a whole, can you see how that would easily amplify itself further? Any new catalysts that develop in the system are going to have this greater imbalance, and will in turn amplify the imbalance. In the end, you can expect very few stereoisomers of the same chemicals. The only reason that it is a problem in laboratory synthesis is that we have relatively few (compared to nature) types of different catalytic reactions going on to amplify differences. It's like doing laboratory synthesis of a chemical, using varying purity of reagents. If all of your reagents are 100% pure, your end product would be 100% pure (assuming that there's only one pathway the reactions can take, there's no rate of reaction problems, you can actually achieve 100% purity, etc). What if your reagents were 99% pure - will your end product be 99% pure? No - the impurities will help introduce alternative paths that the reaction can take; your end product will likely be notably less than 99% pure. What if you used 90% pure reactants? Depending on what you're synthesizing, you may not get much of it at all as an end product. It's part of nature: imbalances tend to amplify themselves in iterative environments (that's why we'll never be able to predict the weather very long range... well, that and quantum theory). Why would you expect differences in ratios not to amplify themselves in a prebiotic earth? Please explain. Secondly, I've already shown that not every reaction is heavily cross-inhibited, and gave an example of one reaction (which took just a matter of minutes to find) which shows *no* cross inhibition. Why? Because of my initial point: That, depending on the situation, different stereoisomers may tend to bond preferentially with their own types. And, you have so far done not a thing to address that how, once a hypercycle begins with a given chirality, that chirality is "locked in". I would like to add that you've been focusing on attacking my knowledge of the subject just because I was unaware of how they determine which molecule receives which name - in response to a post where you showed *your* lack of knowledge on other related subjects - and are avoiding my core points (listed above). I'm not trying to claim to be an expert on the subject. But I would like my points of contention addressed as much as any other poster.
quote: In a single reaction? Of course you're not going to get much of a ratio (although, there are some possibilities**). After 10,000 iterative reactions? You'd be lucky to have even a slightly racemic mixture. Also, here's another interesting theory (genetic takeover). I wouldn't put any money on it yet, but it's an interesting concept. ** - In reference to the Coriolis Force method, there is already some good evidence to back this up; pollutant conentrations in polar bears, for example are sometimes heavily chiral, despite the original pollutants being a racemic mixture. How would you account for this? Clearly, there is *some* sort of natural enatioisomer-selective process going on, and it varies from location to location. ------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
quote: Fair enough.
quote: DNAunion, prophet of the God of the Gaps.
quote: Are you familiar with a Wimshurst Machine? It's a neat electrostatic generator that uses induction to generate power. That is, an imbalance in the charges of the plate is amplified by the process. A curious thing about it is which terminal ends up positively charged and which one ends up negatively charged: it's random. What happens is, it is essentially impossible to have the two disks have precisely the same charge on them. However minutely different the charge is, it gets amplified with each pass. That is exactly what I am suggesting in this case. A slight imbalance of one catalyst, over long-term iterative processes, leads to a major imbalance of end products. Play "God of the Gaps" all you want, but don't fail to address the meat of the issue.
quote:quote: Only if you have a completely pure solution - i.e., free from chiral catalytic influences. When the catalysts are chiral, an imbalance in the ratios betwen catalysts will lead to an imbalance in the end products. When your next line of catalysts are the ones produced from the previous go-round, you get a further imbalance. And a further imbalance, and further, etc.
quote: As I pointed out and referenced earlier, only certain types of chemical synthesis suffer from cross-inhibition.
quote: Arent you forgetting about enantiomeric cross-inhibition?[/quote] Aren't you forgetting my reference? Furthermore, I should add, cross-inhibition is only a problem when you're trying to build a *specific* chemical, through a *specific* pathway, under which the pathway works in a chirally pure solution but has inhibition in a chirally imbalanced solution. Here, we're talking about a near incomprehensive number of different chemicals in the same solution. This sort of pathway inhibition is virtually irrelevant. Let me put it another way. You you're specifically trying to spell the word "AUSTRALOPITHECUS". However, so long as the K key exists, whenever you try to type O-P-I, the K attaches intstead of an I, inhibiting the process. Ok, but what if you first created AUSTRALOP, and ITHECUS, and then joined them? What if you created AUST, RALO, PITH, and ECUS, and joined them? What if HOMOHABILUS functioned the same or nearly the same as AUSTRALOPITHECUS? Etc. Your strict laboratory synthesis analogy is about as unlike a prebiotic earth as you can get, where you have countless different types of reactions going on at once. The more different routes something can take, the less relevant a certain route being inhibited is; in fact, for every route that you have inhibited, odds are you're creating a new possible route. And, as I mentioned before, even in a laboratory synthesis environment, cross inhibition is not always an issue.
quote: Look, do you see me making fun of you? I could likewise start sentences with, "Does your invisible friend in the sky ... ".
quote: That's a given, now isn't it, in most cases with a chiral catalyst?
quote: You're one to speak.
quote: I'm not discussing a specific catalyst, just catalysts. DNA, don't be a pain: you know very well that if we knew the exact route that abiogenesis took (even if it were your "poof, here's life!" method), there would be nothing to discuss. We're here to discuss theories as to what could lead to enantioselective properties, not trade insults over the gaps in our knowledge.
quote: Where do you get a low production rate of polymers from?
quote: There have been a number of theories on the rates of hydrolysis versus polymerization, with varying "wet" and "dry" theories. One such theory involves an in-between, with early polymer forming in the gaps between clay particles.
quote:quote: Why do you expect spontaneous racemization when you're using chiral reactants?
quote: A non-issue - see above. You can poison specific polymers in a laboratory style environment, but you have yet to evidence that it poisons polymer formation in general.
quote: How do you conclude that this would occur?
quote: Once again, introducing the "God of the Gaps!" I can just picture creationists in the 1800s now... "You say that the earth is billions of years old... and yet, we know of no way that the sun could be more than a few millions of years old - the best that you can come up with for its energy is "gravitational collapse". What, is there some "mystery, magical energy source" powering it that we don't know of? That has not been demonstrated experimentally.". The God of the Gaps is continually being forced to move into a new gap. Are you sure you want him in this one? That is why we discuss possibilities, not absolutes, when we're discussing gaps in scientific knowledge. Shoving a God wherever you see a gap is not a good plan for advancing human knowlege.
quote:quote: One could apply that exact same argument toward the weather. Having turbulence in the atmosphere is not an equilibrium state, and so the world should balance itself out toward a simple constant atmospheric Coriolis flow. Does it? Part of the nature of iterative processes is that errors magnify themselves tremendously. Take a class on chaos theory some time, then get back to me.
quote: Explain?
quote: It's a given. No mixture is ever exactly even.
quote: Or whatever early life was based on, which may have nothing to do with life as we know it today.
quote: Why are you requiring two catalysts, again? And why must one of them be a polymerase (assuming that you mean according to current usage of the term, DNA and RNA polymerases, although you could be meaning it in a general sense)?
quote: Actually, given that, it is assured. Given that differences amplify themselves over time, as they are observed to do in many systems, then it is assured. The question is whether they amplify themselves in this particular system. Next week I'll look to see if I can find any studies on the subject; you do your research as well. Of course, remember, we're not talking about a laboratory synthesis environment with a single iteration. We're talking about an environment in which the products of the first reaction are involved in the second, and those products in the third, etc, for billions upon billions of iterations. ------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
DNAunion:
You're back to your old habits of A) splitting up individual posts into multiple, making it very hard to reply to, and B) focusing on personal attacks. If you keep this up, I will cease to respond in this thread. You have been warned; don't expect another warning.
quote: It's implicit in your line of argument. Because, by your line of argument, if not every reaction receives a high degree (or any degree at all, in the case of many reactions) of cross inhibition, then it's not a problem: it only poses problems for *particular pathways* to develop early life. There are countless possible pathways. Your argument, unless all reactions have the same degree of inhibition, is thus near useless.
quote: Now we're back to the GL? Nice try at a dodge there, but this conversation wasn't on the subject of the GL. Let me ask you a question - since you seem to have this huge problem with the concept of how much of a sample size has been observed: What percentage of possible proteins have we looked at that are the length of the GL to test to see whether they're ever self replicating? The ghadiri ligase is, what, 32 amino acids long? We're looking at 4.29e41 possible combinations here for a protein of that length. You have a very serious problem with the concept of the percentage of total sample size observed that you have displayed again and again, and it gets very frustrating. Please quit pretending that we have observed even a tiny, remotely statistically significant percentage of total possibilities. Even in our proportionally tiny percentage of self replicators that we have observed, there are going to be countless different ways such a protein can be formed. Given this, the odds that there will be routes with no cross inhibition seem to be almost a given.
quote: You seem to accept evolution (just not abiogenesis), right? If that is the case, then look at what an undirected process has accomplished since then (or do you believe in "directed evolution"?) "Synthesized in the lab, not in nature". Ah. Just assuming that there are 10 tons of chemicals and solvents involved in brand new, documented organic chemistry expierments being conducted each year on the subject of abiogenesis (not likely, but let's be nice. ), Earth's oceans alone (0.04% of Earth's mass) have a mass of 1.35 quintillion metric tons (1,350,000,000,000,000,000 metric tons). Even assuming that only 0.1% of the oceans were involved (and that nothing on land was involved), that's still giving a volume of 1,350,000,000,000,000 metric tons of reactants operating for a billion years. That is *Far Better* than in a lab. Of course, you won't accept that, because in your worldview, only directed things achieve amazing results, right?
quote: Why? It has preposterously more possible chances in nature to occur. Unless you feel there is some sort of laboratory situation that cannot occur in nature - and if so, please name it.
quote: That one was about hijacking earlier, much simpler forms of life. The sample concept presented was in selective growth of clays, in which different types of crystals compete with each other for further mineral deposits. Deposits of organic material on the surface of the crystals could aid in such selection, and these deposits would likely be chiral (corresponding to the type of crystal substrate they're growing on). Eventually, with a much greater range of possible chemistry, the organic component took over. Again, though, I think such a concept is still too speculative, and I'd like to see more research done on whether it is possible for different clays to have competitive selection.
quote: It must have changed since I looked at it then, because I was able to access the full text the other day for free. I'll summarize: the distribution of a number of organic pesticides has been found to be chirally imbalanced in the world's oceans, leading to a chiral imbalance in wildlife.
quote: And here's a quite with my emphasis added
quote: You continually ignore the frequent use of the word "and" in the text, taking only from one side. The model seems to postulate both on the level of lifeforms *and* on biochemistry itself. Let me add again that a chiral imbalance is not needed, as I have discussed in the first part of this post. But if it was, here's yet another way it could have occurred - a film at the surface of the water, which deals with the water/air border (how many possible methods do you need?) Of course, knowing your love of quotes, you'd probably just ignore the article and extract an out of context quote, such as "Theories on the emergence of the homochiral biopolymers of life at prebiotic times suggest the involvement of enantioselective reactions starting from heterochiral mixtures of alpha-amino acid and nucleic acid precursors (1-7). Polymerization reactions of racemates in isotropic media would lead, however, to formation of polymers comprising a random sequence of left (S)- and right (R)-handed repeat units in a binomial distribution (8). Thus, the probability of obtaining oligomers with homochiral sequence will become negligible with increasing length (9-11)." to try and convince people who don't know better. Almost any assembly that occurs on a two dimensional inorganic surface would be expected to be subject to the chiral influences of that surface. And, as I stated before, that is not even necessary, since any chiral imbalance or influence would be expected to imbalance the system as a whole, especially any that gets closer to self replication
quote: Thank you for being so mature Do most people you debate with end up getting sick of you in the process and leaving? If so, you shouldn't be surprised.
quote: There is absolutely no necessity that the first forms of life had to have been based on what life currently is based on. That is why we need to discuss enantioisomers in general.
quote: In limited cases; it takes about 5 minutes of searching to dig up a process in which there is *no* or *minimal* cross inhibition. And, as I've mentioned several times, that's only relevant for a particular route of creating a particular molecule - neither of which we are discussing when talking about abiogenesis. There are near countless possibilities under each category (routes and molecules) that can work just fine.
quote: Yes.
quote: No. "chirally pure" - Google SearchIf you'd rather I use the term enantiomerically pure, that's fine, so long as we're on the same page. quote: Do you realize how bullheaded you look when you deliberately ignore what a person is saying? Did you even read the analogy?
quote: 2) Exactly what method are you proposing for your deity generating an enantiomeric excess of left-handed amino acids and/or right-handed ribose? Or is this going to remain some unnamed mystery god-magic? 3) How did your as-of-yet unidentified god-magic come to create preferentially one chiral form? 4) How did your as-of-yet unidentified god-magic maintain the chiral preference over an extended period of time? Was there some other chiral catalyst making it? That said (turning it back on yourself), and with me pointing out yet again that we have looked at such a tiny percentage of the sample size that it's about as deceptive as you can get to ask for an exact route, I will repeat what you quite obviously did not read in your skipping over my analogy (and my entire discussion about how synthesis of a product with varying purity of reactants generally has the production rate of the end product fall off faster than the purity of the reactants - why should I even bother when you don't read what I write?): There always is an imbalance, even if incredibly small. In most real-world applications, imbalances tend to magnify themselves when subjected to iterative processes instead of converging.
quote: And don't pretend that what *I* said - that the odds of it being a particular self replicator that we discover, and having been made through the exact process that we make it - are so small as to make them essentially zero. The number of possibilities out there makes it incredibly likely that the first self replicator is *not* something that we have ever observed, and that even if it was, it would *not* be produced through the route that we produced it.
quote: Yes, I know, you have far more time for this than I do. Is that something to really be proud of? Again, why are you insistant that DNA and/or RNA had to be first? I would expect the first life to be a simple ligase that makes broken copies of itself (anything that is "close" to itself increases the odds of random interactions producing another copy of itself). This would be replaced by a ligase that makes correct copies of itself with correct source material, and broken copies of itself with incorrect source materials. This would be replaced by a ligase that either itself can handle a wider range of source materials, or can also create another ligase that creates correct and/or broken copies of the source materials; etc. This progresses until you have a fairly stable hypercycle. DNA or RNA would be a later introduction to the system. "RNA world" is a fairly old concept (1967, I believe); it had some reinvigoration in the early 1980s with the discovery of catalytic RNA molecules, but is anything but universally accepted.
quote:quote:quote: ... which effects *some* pathways for *some* molecules, but not *other* pathways, and not on *other* molecules, out of tredecillions of possibilities molecules with, perhaps, quindecillions of possible assembly methods, for something merely as long as GL.
quote: 1) Inorganic substrates (incuding the water/air boundary - any 2d substrate will do).2) *Any* level of imbalance should get magnified. quote: Not stop. Produce a mixture with an enantiomeric excess.
quote: You just claimed that you're not trying to state that all synthesis has enantiomeric cross inhibition. Are you saying that, now?
quote: Wrong. In a laboratory environment, that may happen when you're dealing with a very limited set of very pure reactants, but in the real world, those chemicals are not going to stay short for long. There are too many things that could possibly react with them to either tear them apart or attach new things to them. You're dealing with your directed, single pathway logic again. That's not at all what is proposed with abiogenesis.
quote: Racemization in peptide assembly when a ligase or the subunits has an enantioisomeric excess? How? Again, there will always be minute excesses, so you have to show that the ratios *converge* instead of *diverging* when there's an excess, in an iterative process (i.e., when the results of one process become the reactants in the next).
quote: Ah, finally an applicable quote. And my response? It's already been shown to occur. Sorry, there! Asymmetric autocatalysis and amplification of enantiomeric excess of a chiral molecule
quote: quote:quote: So typical. You respond to a point with offhand dismissal. Here I am, trying to answer each and every one of your points, and you ignore me with a wave of your hand on 2/3 of the things that I write. By the way, I have taken classes on both. (Preparing for another insult from you...)
quote: How is there a decrease in entropy? And need I mention that the trend of increasing entropy only is law inside closed systems? P.S. - Seing as you're so fond of quotes, allow me to turn your favorite old argument back on yourself. If all of these scientists are so sure that there's some sort of problem with abiogenesis, why do they believe in it? ------------------"Illuminant light, illuminate me."
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
I've warned him about this - and now I'm going to live up to my word and not respond. I've never found a person with a more annoying "debate" style here - and that says a lot, seing as how we have teenage YECs at this site.
------------------"Illuminant light, illuminate me."
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