Well, it is somehow clear that the soil we are living on is perceived as opposed to the skies above us from very ancient times on.

Also from ancient times on people (not all of them, I suppose, but some) knew that there were some more "patches of soil" that can be reached by sea.  The idea that the whole system of seas and continents/islands is not limitless but has some form is also very old but I don't know if there were other opinions claiming the world (including sea) to be infinite.

The idea that the earth is a ball is not invented by Kopernikus either, the ancient Egyptians had a similar theory, only it was temporarily out of fashion. So I don't think we can find out the name of the person who first proclaimed it.

As for the word "earth" I don't know its etymology but it clearly is akin to the German word Erde, which means Earth but also "soil".

That's a corker of a question (and when I have finished offering my answer, I'll give it five out of five). The first person to realise that they were living on a planet, would probably have been the first person to realise that the sky above us contained other planets, so my first guess would be the Babylonians (somewhere around the 3,000BC mark), but they would have been able to confirm that until the invention of the telescope which would put old Gally (if you will excuse the nicknaming of him) in the frame in the mid 1600's

Chance

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Surely nobody "invented" the earth? 

Roger Everest