Re: Who named our planet 'earth?'

We do not know, and I do not think there is really any way of knowing.

It may not be obvious to you, but what you are really asking is a linguistic 
question. It is not a scientific question or even an historical question.

In English, 'earth' has been only recently (a few centuries) used for the planet 
-- 'world' becomes more common the further back you go. But 'earth' has been used 
for ground or soil much longer. 'earth' is also obviously and closely related to 
the German 'Erde' which has a similar and probably longer usage for both planet, 
ground, and soil.

When language gradually changes like this, and especially when a word is old, and 
has related forms in other languages, its use can seldom be traced back to a 
single 'namer' or 'inventor'.