Having not delved into Oddworld cosmology, astronomy, geology, or indeed any of the sciences in regards to the study of the planet (which would answer quite a few queries) we assume that the planet of Oddworld was formed similarly to Earth, barring any irregularities. Which, might I add, is nothing to do with the Big Bang theory, which concerns the origin of the universe, not planetary development.
You want the nebula hypothesis.
__________________
| (• ◡•)| (❍ᴥ❍ʋ)
|