If the Earth split apart none of us would survive (spoiler)
Having seen this as a little kid I remember even then thinking it was ridiculous for there to be a crack in the world to begin with, but that if Earth did split apart - even because of a bomb, and if it did split apart to create another moon there is no way any people or much life of the planet would survive.
So, in other words it was pretty, pretty, pretty, pretty, ... pretty, ridiculous.