Hello again, Moon:The Earth is supporting itself.
The reflexive pronouns -- in this case, ourselves -- reflect the subject.
In this case, the earth is the subject. The reflexive pronoun referring to a singular inanimate thing is itself.
Thus, the sentence would have to be
To use ourselves, a sentence would have to be
We have to support ourselves on the Earth.
Your original sentence is correct. The earth is not supporting itself, and we are not supporting ourselves; instead, the earth is supporting us.