Ok, I think I will leave a kind of last comment/consideration as well, about what we have discussed so far
Well, for me this is the most interesting part about lord of the rings. There is nearly nothing illogical in it and this is the thing which makes lotr different to most of nowerdays fantasy stories.
If you look at the maps: Everything fits perfectly and if you look at the time they use for wandering through middleearth:
It's realistic. (not like the 'teleport to Gundabad and back' of the third movie)
Additionally all the names of rivery, mountains and so on are also always fitting.
But on the other hand... perhaps it's just that we germans are unfunny and can't just enjoy such things without thinking about engineering... 
Gnomi, I never wrote or implied that the whole Universe of Tolkien might be totally unrealistic or illogical; it's the exact opposite thing
But, given that (as you have rightly exposed above) the Tolkien's Legendarium is a realistic (very realistic) representation of a fictional World (a kind of diverse and complicated Reality very similar to ours, and governed by similar natural laws), it's still not REAL.
And thus, as a fictional Universe, it can't be approached 100% the same way we approach our Reality, especially with very specific and holistic scientific reasonings.
Let's say that those scientific reasonings could be used to describe a lot of essential and basic things of Arda, but, in the end, they would naturally fail to explain everything, eventually failing to give an useful and precise answer to the various questions and 'mysteries' that are deeply part of Eä (the material and physical Universe).
The high and impressive lifelikeness of Arda is perfectly integrated with its 'Magical Nature', which is, as we conveyed in our previous comments, the sum of all the unknown and natural powers and knowledges of superior (or just different) sentient beings (in this case, mainly Elves and Ainur), who shaped and modified the course of the events of the World and the World itself with their natural powers and actions.
That's why, as I referred to above, one could never really find a scientific and technical explanation (based on our standards) for the nature of the Two Trees of Valinor, the 'Immortality' of the Elves, the long lifespan of the Númenóreans and the Dwarves, and an enormous amount of other things...
What about, for example, the Great Cataclysm that changed the Shape of the World, the Corruption of the Elves into Orcs, the unknown Arts in the creation of the race of the Dragons, or the holy Magic which infuses Valimar and the whole Blessed Realm?
These things shouldn't (can't) be explained or approached with our scientific standards of Knowledge, because they would be suitable up to a certain point, and, then, would inevitably fail and made useless.
Furthermore, I don't think that it would be really fair, as someone wrote in the previous comments, dividing the 'world' of the Ainur and the Elves from the one of the Dwarves and Humans, inferring that the former is the real and only 'magical' one, and the latter is 'our' real Reality, in which we can easily explain everything with Science.
There is only one Arda (World), and, since it was created and shaped by the Ainur in the first place and, later, inhabited firstly by the Elves (among the Children of Ilúvatar), these two races belong to it as the Dwarves and the Humans, and their 'Magic' is a fundamental and indivisible part of it.
To conclude this long post (I'm sorry
), I really believe that, apart from the interesting and realistic traits of Arda and discussions about its foundations, there are things that must be necessarily accepted as they are, recognising our impossibility or very vague and imprecise capability of exhaustively explaining them.
As if we questioned what truly is the 'Free Will' of the Valar, and, consequently, why they do not have higher 'ambitions' of Power and always inevitably follow the Will and Authority of Eru as the only Truth, without questioning it (like the Angels towards God in Christianism).
Or trying to understand the real Nature of Ilúvatar (God), and how exactly it (Eru has no gender) is capable of having always existed in the Past (before the Ainur), always existing in the Present, and existing forever in the Future.
There are no possible scientific or technical answers to these matters.
Not because you are Germans, but because we are Humans, and thus can't understand things beyond our comprehension of Reality
I think that this pivotal theme is perfectly described and dealt with by Tolkien, even if it's present in very subtle ways.
The Tolkien's Writings are primarily Fantasy texts, and they had better remain so.
I hope we can agree on that
Greetings
