As I was correcting a paper on Earth day I gave to my students, I came upon a grammar notion I was not really sure about. The sentence which I was dwelling upon is the following: “He feels sad because he doesn’t know what he can do to save the earth.” I read some suggestions on this forum about “the Earth vs Earth” but they still don’t answer my question. In my head, it sounds best to say: “to save the planet”. Like this there is no confusion. But can we say “to save the Earth”?
Yes, when you are talking about the planet, you can use ‘the Earth’ instead. What your student wrote sounds perfectly natural.