Posted: Sep 29, 2018 3:40 pm
truelgbt wrote:Rumraket wrote:truelgbt wrote:This reminds me of my disappointed reaction to the Miller-Urey experiment which also started by introducing products of DNA (methane, ammonia) which, IMHO, is almost equivalent to "stacking the deck" or "planting evidence" into the experiment. Yes, I understand they were trying to mimic the prehistoric environment of methane from volcanoes, for example, but studies show that about 95% of methane on earth is due to life forms, i.e. products of DNA, so methane itself can, and is, largely considered to be a product of DNA.
This makes no sense at all. There are clearly nonbiological sources of methane. You even write yourself that 95% of extant methane is produced by life, but then 5% isn't. So using methane can't be stacking the deck in any way.
So going back before the origin of life, there was volcanoes, and they would have produced some methane.
Methane and ammonia are not just products of volcanoes; they are also produced by bacteria in much larger quantities than volcanoes by a ratio of 95:5. Therefore methane and ammonia are not just associated with DNA, they are considered products of DNA i.e. products of life, not just by me but the scientific community in general. You will not find any article denying that methane and ammonia are associated with bacteria. They are.
Disregarding whether those ratios are correct, the statement is completely irrelevant. The relevant questions to ask are: What compounds were plausibly available in the prebiotic environment before life originated? Whether those molecules are also byproducts of life today is besides the point.
From what compounds did life originate? Well if ammonia and methane was actually available in the prebiotic environment before life existed, then it is entirely possible they were involved in the actual origin of life. And then the next relevant question is, where was it available, in what quantities, and what local environmental energy sources, physical processes, and environmental cycles could have acted on them? And if they did, what would that produce if anything?
Whether life that later evolved and has DNA then also evolved the ability to produce these compounds is completely irrelevant. Were they or were they not available in the prebiotic environment before life had evolved? If they were, then using them in an experiment is entirely fair. Again, then the next questions to ask is where they were available, in what quantities, and so on.
truelgbt wrote:The higher standard for performing an experiment to generate 'life' in the lab is to exclude ANYTHING associated, even remotely, with life. No methane, no ammonia, etc. But that's just me. I prefer a higher standard.
Your "higher" standard is nonsensical, because there is no limit to this. Pretty much EVERTHING is known to be somehow associated with life. There is life that produces hydrogen and even water. In fact many chemical reactions in your body have water as a byproduct. Why stop there? Your're made of carbon and oxygen atoms too, and even electrons, so why not exclude those? Your standard is illogical.
The only relevant question to ask is which compounds were plausibly available in the prebiotic environment. To get clues about that we can ask geochemists and planetary astronomers to see what could be produced by basic geological and atmospheric chemical reactions, and what is found on lifeless planets and in interstellar clouds. Those are then the relevant compounds to potentially include in an experiment.
truelgbt wrote:The lower standard, IMHO, is to introduce all kinds of products of life into the experiment such as methane, ammonia, organic materials, etc. So, for example, if you are trying to generate life in an experiment and introduce materials already produced by life into the experiment, what have you demonstrated?
Well if there is some physical mechanism by which those compounds can assemble into more complex structures plausibly related to life, and they do so without any of the evolved molecular machinery found in life, then you will have demonstrated a physical mechanism that could plausibly be relevant to the origin of life.
Again, if those compounds used are already known to have been available in the prebiotic environment before life even originated, because they can be and were produced nonbiologically, then that directly relevant to the origin of life.
truelgbt wrote: In other words, if your experiment begins with products of DNA, and your experiment ends with products of DNA, what have you demonstrated?
DNA doesn't have products. It's like a hard-drive, it doesn't really "do" anything by itself. It contains sequence-information which is read and executed by some rather elaborate protein and RNA molecules, which themselves were produced by such RNA and protein molecules all the way back to however they first originated.
So the answer to your question actually depends very much on what the starting and ending compounds are. It is irrelevant whether those starting compounds are themselves constituents of DNA, or mid-or-end-products somewhere in cellular metabolism.
It could be the case that one of the ways that RNA or DNA first emerged was by a nonbiological organic chemical reaction involving ammonia and carbon monoxide (say). So if an experiment that mimicks a plausible natural environment (perhaps a volcanic setting of some sort) produces a DNA precursor from ammonia and carbon monoxide, then that experiment has demonstrated that a particular volcanic setting can produce DNA precursors from ammonia and carbon monoxide.
Again, the relevant question is: Was ammonia and carbon monoxide, as used in this hypothetical experiment, actually available in those quantities in such volcanic settings before life originated?
It is completely irrelevant whether organisms that live today can make ammonia and carbon monoxide. What is relevant is if they also existed and could be produced in the prebiotic environment before life. This is again where geology and planetary astronomy becomes relevant to answering such questions.
truelgbt wrote:I am not trying to be difficult but just asking the difficult questions that everybody should be asking.
But your questions are nonsensical if not stupid, so noone should be asking them. They should be asking, among other things, what compounds were actually available in the pretiotic environment?