Here's an interesting thought about Mata Nui...
What if the island is actually the first stage of the solitary continent, Pangea? (Dinosaur fans know what I'm talking about.) When shown on a map, it is generally the only landmass on the entire planet--with an exception of its own, smaller coastal islands. The island may have have eroded into other forms, (within a long period of time) eventually transforming into Pangea, which evolved into what we know today.
I thought it was pretty logical...