That goes WAAAYY back in antiquity, even well before the bible was written.
"Earth", when used in a different context, also means "dirt, "soil", or "land" 9as opposed to "ocean" or "sea"). In this context, "earth" is used to refer to whole dirty, soiled, land-mass of a planet.
In Genesis, the Hebrew word "erets" is used to indicate "earth" right in Genesis 1:1! The same word, "erets", is used in the rest of the Old Testament to indicate land, dirt, soil, or the whole planet. We thus KNOW that the idea of using the same word for all meanings goes back at least 3500 years.
Just WHO started this idea is completely unknown. That record was never kept.
the name "earth" is an Anglicized word. It is not the same in all languages. Why "earth" was chosen is ALSO unknown, but there does seem to be some relationship between "Earth" and the Hebrew "erets", indicating a possible biblical connection.