Did the events in LotR take place on another planet?

The first was in the Prologue. It is there stated: "Those days, the Third Age of Middle-earth, are now long past, and the shape of all lands has been changed; but the regions in which Hobbits then lived were doubtless the same as those in which they still linger: the North-West of the Old World, east of the Sea." (FR, 11). Since no other reference is made to this matter either in the Prologue or in the main narrative, it makes little impression on most readers, but is clear enough once pointed out.

The second was in Appendix D, which presents lore on calendars in Middle-earth. The discussion begins as follows:

The Calendar in the Shire differed in several features from ours. The year no doubt was of the same length (*), for long ago as those times are now reckoned in years and lives of men, they were not very remote according to the memory of the Earth. [RK, 385 (App D)]

(*) 365 days, 5 hours, 48 minutes, 46 seconds.

There follow excerpts from three letters wherein the matter is further discussed.

'Middle-earth', by the way, is not a name of a never-never land without relation to the world we live in .... And though I have not attempted to relate the shape of the mountains and land-masses to what geologists may say or surmise about the nearer past, imaginatively this 'history' is supposed to take place in a period of the actual Old World of this planet. [Letters, 220 (#165)]

I am historically minded. Middle-earth is not an imaginary world. ... The theatre of my tale is this earth, the one in which we now live, but the historical period is imaginary. The essentials of that abiding place are all there (at any rate for inhabitants of N.W. Europe), so naturally it feels familiar, even if a little glorified by the enchantment of distance in time. [Letters, 239 (#183)]

... I hope the, evidently long but undefined, gap(*) in time between the Fall of Barad-dûr and our Days is sufficient for 'literary credibility', even for readers acquainted with what is known or surmised of 'pre-history'.
I have, I suppose, constructed an imaginary time, but kept my feet on my own mother-earth for place. I prefer that to the contemporary mode of seeking remote globes in 'space'. However curious, they are alien, and not lovable with the love of blood-kin. Middle- earth is ... not my own invention. It is a modernization or alteration ... of an old word for the inhabited world of Men, the oikoumene : middle because thought of vaguely as set amidst the encircling Seas and (in the northern-imagination) between ice of the North and the fire of the South. O. English middan-geard , mediaeval E. midden-erd, middle-erd . Many reviewers seem to assume that Middle-earth is another planet! [Letters, 283 (#211)]

(*) I imagine the gap to be about 6000 years: that is we are now at the end of the Fifth Age, if the Ages were of about the same length as S.A. and T.A. But they have, I think, quickened; and I imagine we are actually at the end of the Sixth Age, or in the Seventh. [Letters, 283 (#211)]

... I have not made any of the peoples on the 'right' side, Hobbits, Rohirrim, Men of Dale or of Gondor, any better than men have been or are, or can be. Mine is not an 'imaginary' world, but an imaginary historical moment on 'Middle-earth' -- which is our habitation. [Letters, 244 (#183)]

References:

FR, 11 (Prologue);

RK, 385 (Appendix D);
Letters, 220 (#165), 239, 244 (#183), 283 (#211).

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Was the northwest of Middle-earth meant to actually be Europe?

Last modified: Sat Aug 19 19:24:42 1995 

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