"The geosphere is the mosly solid, rock part of the Earth." said the Florida ScienceFusion Textbook. It goes from the surface of the Earth to the very center of the Earth. The 1st layer is the crust. The 2nd layer is the mantle. The 3rd layer is the outer core. The 4th & final layer is the inner core. The mantle has the most mass & the core is the most dense.