What is the pure mallu word for earth?
If we are referring to earth (land), I guess it would be നിലം. I suppose it comes from the root നില്് meaning "to stand"; of course, the land just stands there and doesn't go anywhere. കര is another word for land; it also means shore (cf. അക്കര). I don't know it's etymology, though.
If we are referring to earth (soil), I guess it would be മണ്ണു, coming from the root മണ്്.
What about planet earth? ഭൂമി, ഭൂഗോളം etc are "obviously Sanskrit". So what would the pure mallu word be?
Or did the concept of earth as a planet did not exist until the advent of Sanskrit sub-culture?
P.S. Did you know that there are (at least) three one-letter words denoting earth? These are all obviously Sanskrit. They are: ഭൂ, ജ്യാ, ക്ഷ്മാ