I'm not sure how indepth it is possible to make this. Germanic paganism understood the ground as personified by a goddess, Jörth, a direct cognate to Earth. This was used to translate Gaia and Terra, the Greek and Roman equivalents. The Greeks and Romans knew the Earth to be a globe (Eratosthenes had even calculated its circumference around 200BC), hence this sense of the word found its way into Germanic language as well. It is thus an ancient term even in this specific sense, going back well beyond even Old English.