Which earth layer is less dense than the layer above it?

The deepest places on the earth are in South Africa. Mining companies trying to extract gold and diamondshave mined into the earth about 6 km (about 3.5 miles). No one has gone deeper into the earth than the South African miners (with heat-resistant clothing) because of the heat and pressure at these depths prevents humans from goingmuch deeper. If we can’t go very deep into the earth, how do we know what is below the surface when we can't see it? Isaac Newton (the scientist that discovered gravity) was one of the first scientists to develop theories about the structure of the earth. Based on his studies about gravity, Newton calculated the average density of the earth and found it to be more than twice the density of rocks on the surface. Newton realized that the inside of the earth had to be much denser than the surface.