Earth crust layers

Crust
-Average depth beneath the continents is about 40 km,and 10-12 km beneath the ocean,
-Chemical composition of the most complex as a result of geochemical differentiation during formation of the Earth and the physical and chemical changes which subsequently occurred.
Continental crust-acidic aluminosilicate rocks (granite)
-SIAL (Si + Al),
-Miss at the bottom of the ocean.

Oceanic crust-mafic rocks (basalt) + covering sediment deposits average thickness in the oceans ≈ 450 m,
SIMA-(Si + Mg)
In basaltic crust are sometimes printed and rocks from the upper mantle.
Lithosphere (crust + upper mantle)
The lithosphere is the common exposed structural(Tectonic changes).Structural changes usually are caused by the dynamics of asthenosphere.
The two surfaces of discontinuity(Wiechert-Guttenberg(Core / sheath) and Moho (crust / mantle).
Isostasy
Isostasy is a balance between the dipped pieces (blocks) broken off the Earth crust that floats on the plastic and denser upper mantle (like a piece of wood or icebergs that float on water).Simplified, eg by Buoyancy, body immersed in water because of its weight oust the amount of water equal to their volume.Simply put, we can imagine the broken off pieces of bark to dive into the upper mantle and in accordance with its weight of push mantle, where each piece is in equilibrium with the adjacent piece because each piece has the same mass.
If we imagine that parts of the crust and upper mantle form separate vertical columns, then it is at the bottom of their bases the same pressure.
GRAVITY
The force of gravity between two objects varies depending on the mass of objects and their mutual distances according to the relation:
         mA* mB
G = k --------------
              l * l

The force of gravity increases with the mass of observed objects and the reduction of their
distance (between the celestial bodies, stars and planets and their satellites is much higher than between two objects on the Earth).