Tom,  human beings still know so very very little about everything at the bottom of the ocean and even LESS about what lies within the earths inner shell.   there are still great mysteries in this world, its just we've reached the upper limits of how viable doing research on those mysteries are,  after all we'd still probably be doing a ton of guessing still about space travel if we didn't have two super powerful nations having a great big pissing contest to give the motivation needed to spend trillions in trying to achieve the impossible,  we don't quite have the same motivator to find out if the earths core has mole people in it XD