Where does “ertha” come from?

ertha (Old Dutch) comes from Proto-West Germanic erþu, from Proto-Germanic erþō, from Proto-Indo-European h₁er- — earth.

ertha (Old Dutch): earth

Definitions

Step	Language	Word	Meaning
1	Proto-West Germanic	erþu	earth, world; earth, soil
2	Proto-Germanic	erþō	earth
3	Proto-Indo-European	h₁er-	earth

ertha — Etymology, Origin & Word History | Etymology Explorer