Posted: Oct 15, 2018 1:58 am
truelgbt wrote:Anytime an experiment starts with a substance which is KNOWN to be produced by the very thing you are trying to generate in the experiment, you weaken the implications of the experiment's results - you do not strengthen it.
No, for reasons already explained. The only relevant question is if those compounds were available in the prebiotic environment in sufficient quantities. If they were, then it doesn't matter than life would then later evolve the capacity to make them. If they already existed, then they were available and that is the only salient, relevant fact.
truelgbt wrote:For example, let's start with phosphates, sugars, and nitrogen bases and try to see if DNA is the end result.
Well if those compounds really were available together, in the relevant quantities, in the prebiotic environment, then there's nothing wrong with conducting an experiment starting on that premise.
That is of course a big question, and there is no consensus on this, so for that particular collection of compounds I would agree that an experiment started on that premise is begging the question. But this is different from saying that an experiment will by definition be begging the question by starting with these compounds merely because living organisms can make them today. It doesn't matter that life today can make those compounds, what matters is only whether they were available in the quantities used in the relevant experiments, in the prebiotic environment.
truelgbt wrote:That is what so many here are proposing that is just SO convincing to them.
Nobody here has proposed anything about phosphates, sugars, and nitrogen bases, nor that it "SO convinces them". You made that up deliberately to make it look silly, but nobody has actually done what you accuse them of here.
truelgbt wrote:And so is the Miller-Urey - how they even got to the status they did is beyond me.
This just reveals you don't understand the Miller-Urey experiment. There are reasons to think the results of the Miller-Urey experiment are not relevant to however life on Earth originated, chiefly that the simulated conditions actually differ from what geologists today think the Earth's primitive atmosphere was composed of.
But the problem isn't that the starting compounds are "byproducts of DNA", because for reasons explained now several times, that is irrelevant. Even water is a byproduct of DNA in the same sense you use the term "byproduct", and so is carbon dioxide. Yet both water and carbon dioxide is thought to have been abundant on the primitive Earth before life originated, so it can't be begging the question to use water and carbon dioxide in an experiment in prebiotic chemistry.
Again, the pertinent questions are:
What compounds were available on the early Earth?
In what quantities?
Were they available together and for how long?
What physical processes operated in these environments?