is also another name for soil or even the ground and in those cases, no upper case letters are required.
now i'm wondering if in the phrase, what on earth, earth means the planet earth or just the ground upon which i'm standing. well the ground upon which my house is standing, in which my chair is standing, upon which i am sitting but you get my drift, i am sure.
now i'm wondering whether or not it's worth looking up.
now i'm wondering about how the phrase get my drift, might relate to the earth and continental drift and wondering if the earth upon which my house is standing is drifting and 