Hell wasn't part of the six days of creation, it's a direct consequence of sin. At the fall of man in the garden of Eden God cursed the Earth. This was the beginning of nuclear decay.
IF nuclear decay isn't constant, AND an initial burst of radiation caused the core of the Earth to melt, THEN material from the lower mantle will melt and fall into the molten core which is why it's expanding.
Is it Christian to warn people that hell is real? Hell is expanding, it's the cause of global warming.
Some of the most vocally opposed to the idea that climate change is real are evangelical Christians. It's ironic since the Bible makes it clear that hell's been expanding since it was kindled at the fall of man.
Deuteronomy 32:22 begins the doctrine of the expansion of hell. The foundations of the world is the Earth’s mantle. It's been set on fire by the heat from hell below, and this is the cause of tectonic activity.