Although the word terra is the usual way of speaking of the Earth, some form of tellūs is also a possibility. The latter is used in this sense most commonly in poetry. According to the lexicon of Lewis and Short, it is defined as:
tellus — the earth, opp. to the other planets or to the sea, the globe
(a word belonging almost entirely to poetry).
My first impression was that you were trying to express "of the Earth", in which case the genitive form would be used. However, the word excelsior is a comparative adjective which suggests the comparison "Higher than the Earth". In that case the ablative should be used. In order to make it clear that excelsior doesn't describe terra (in which case it would mean higher ground), it might be better to use the plural form of excelsior:
Using the ablative form of tellūs:
If, on the other hand, you did want to use the genitive ("...of the Earth"), it would be:
Using the genitive form of tellūs: