It's like this.
The Earth is constantly recycling itself. All matter that is once on the surface of the Earth will end up in the middle of the Earth; and all matter in the middle of the Earth becomes the outside. This planet is constantly changing deep down underneath our feet. I'll tell you what hell probably is. Hell is a place where creatures thought to be extinct live deep in the depth of which we have not yet been able to reach.
We know more about space than our own oceans.
I believe that there are things that we can never know. Unanswerable questions erased by the vastness of time. Experienced by living being if only for a short while. I believe that their are cities and technology that we have not even seen before recycle itself back into the Earth, with it's culture, and it's society. Like the dinosaurs. Only these ancient civilizations predate the fossil record. They have been erased, and ruined into the liquid metal that is our Earth's core. All kind of ancient cities melted away. Super volcanos.
We are actually overdue for the Yellowstone Park volcanic blast. Scientists say that one is a super volcano. It would be like smothering the entire world in ashes. Blocking out the sun. Killing off our crops, our honey bees would die, and they are very important to our crops.
Not to mention an infinite number of ways it could go wrong on the surface, you also have to think about what is going to swallow you whole, like a super earthquake. They say that one day, a huge chunk of Africa is going to break off into the ocean, and cause a terrifying mega tsunami for the entire east coast of the Americas and Canada. This would of course kill everything in its path, but think about the undertow of where part of the continent of Africa is going to break off. An undertow of that proportion would suck the rest of Africa down with it and cause horrifying super earthquakes shaking apart the surrounding area of Africa.