Dear Professor Klein, as long as you are talking about these intelligent reptiles living under ground, please explain this.

Wouldn't the center of the earth have no gravity? If there were a "room" exactly at the center of the earth, and if you were in that room, wouldn't you be experiencing weightlessness? After all, isn't it the mass of the material that causes gravitational effect? And at the exact center of the earth, wouldn't the effect of gravity be pulling you simultaneously approximately evenly in all directions? So, you would be almost exactly weightless, right?

Doesn't this mean that whatever material is exactly at the center of the earth is really weightless? In other words, it is not under pressure of any kind, correct?

Now, as you move further away from the center of the earth towards the outer edge of the earth, gradually, there is an increase of weight because there is more material on one side of you than the other. The side with more material is, of course, the side facing the center of the earth. Doesn't this mean that the highest concentration of gravity is near the outer shell of the crust of the earth, because that is where the most material is on one side of you while the least amount of material is on the other?

Of course the pressures are greater the further you go under ground starting at the surface, because you would have the weight of all the material above you sitting on top of you. We can see this easily in the oceans.

But how does this truly explain the structure of the earth? If you join the kids in the sandbox, and you have a pile of sand in front of you, you can dig a tunnel into the side of the pile of sand, and for awhile the pile won't collapse on your hand. You will have a tunnel in the sand. Could it be that the material of the outer crust of the earth, say, a few hundred miles deep, has been jammed together by gravity, and sort of like the sand in the sandbox, is maintaining its position jammed together in a shell?

So, the Earth might be hollow, just as it was taught in school prior to a hundred years ago. In fact, the hollow earth idea was being taught as late as the 1940's. Maybe the reptiles live in light gravity on the inside of the shell of the hollow earth.