What conditions gave rise to the number of languages spoken in Oceania? Would it be accurate to state
that nearly half the languages spoken in the world are
in Oceania?

The many islands separated by water made for very little to no contact with one another. This lead to the formation of different languages and cultures.

The investiture controversy began as a power struggle between pope gregory vii (1072–85) and henry iv, holy roman emperor (1056–1106).[2] a brief but significant struggle over investiture also occurred between henry i of england and pope paschal ii in the years 1103 to 1107, and the issue played a minor role in the struggles between church and state in france, as well.by undercutting the imperial power established by the salian emperors, the controversy led to nearly 50 years of civil war in germany, and the triumph of the great dukes and abbots. imperial power was finally re-established under the hohenstaufen dynasty. historian norman cantor:

The sun's parallax would be 180 degrees, greater than which you can't get.  so a. would be your anwser