There has been much speculation about the real state of the earth. The Hollow Earth theory has been around a long time, many people have tried to prove it, quite a few films made about this topic.
Here is one theory by Raymond Bernard, who wrote a book called "The Hollow Earth".
In it he states:

Our world is hollow, with the crust of the earth being 800 miles thick. There exists two openings at the North and South Pole, each hole having a circumference of 1400 miles wide. At the centre of the earth is not a molten core but an inner sun which is six hundred miles wide and is 2900 miles from the Inner Surfaces. The diameter of the lip at the opening at the poles is 1200 miles long, thus a person can not see the other side of the opening.
There exists three worlds on our planet, the outer surface, where we live, the middle earth which purportedly is lined with many caverns, tunnels (made by someone), Inner Cities and people who live there and lastly the Inner Surface.
How Gravity works then is the following. For the people who live on the outer surface, Gravity holds them down. For the people that live in the middle earth, the closer they get to the centre of the crust (i.e. - 400 miles down), the less effect gravity will have upon them.
Furthermore Bernard states that the Aurora Borealis that is only visible up north, is the reflection of the inner sun off clouds passing over the opening of the pole. Also that some explorers of the North Pole have discovered the closer they get to the Pole, the warmer it gets instead of the colder.

An explorer called Admiral Byrd in 1947, went to explore the North Pole. He states that he actually entered into the Inner Earth at the opening at this pole. He also states, he made contact with an advanced people in this area who showed him their world and asked for him to take a message back to the surface dwellers and government of their concern about a future vision they had of our destroying our world and since this is their home as well, they of course wanted to prevent this. If such a people do exist, it is theorized that possibly some of the UFOs we see are not extraterrestrial but intraterrestials, as our elder brothers keep an eye on us.
If you would like to read extracts of his diary I include the link:
http://www.v-j-enterprises.com/byrdiar.html

More will be posted on this topic. :tup: