what is middle earth

[The Saucepan Man]

There's a series of maps in the Tolkien Illustrated Encyclopedia (my reference source for anything pre-The Hobbit until I get round to reading The Silmarillion) which shows the development of Arda (the World) through the various Ages to present time (The Fourth Age of the Sun), some 40,000 years after its creation.

Comparing the Third Age of the Sun (the Age in which LotR is set) to the Fourth Age, Middle Earth represents Europe, Asia and Africa. The area in which LotR is set is Europe (the Shire being the UK) with Harad and Far Harad being the Middle East and Africa respectively. The Americas are the Sunlands and Australia is indeed the Dark Lands.

I'm not sure about Mordor being Turkey (I've been to Turkey, it's nice), but it looks about right. Or perhaps Germany, given that JRRT was writing LotR around the time of WW2 (but then again, Germany's a nice place too).

I remember reading somewhere that JRRT thought of Gondor as Italy and Minis Tirith as Venice I think (but without the water).