Here's my Theory:
What if a lizard was sitting next to a railroad track and then a railroad train that's carrying some nuclear waste derails. Then the nuclear waste explodes right on top of the lizard, causing a dinosaur to appear. There is still some nuclear waste so the national gaurd is ordered to "safely" blow the rest of the nuclear waste up. When the missiles hit the remaning train car, one part of nuclear waste and one of the missiles hit the dinosaur at the same time, causing Godzilla.

a nuclear explosion would destroy planet earth.