Crust Thickness Average composition Typical Density Oldest Preserved
Continental ~30-40 km
Double thickness in Himalayas
Granite (wide range) 2.7 (quartz, calcite) ~4 billion years (northern Canada, Greenland, Australia)
Oceanic ~ 8 km Basalt/gabbro (very uniform) 3.0 ~170 million years, western Pacific (tiny older patch in Mediterranean)
Uppermost mantle   Peridotite 3.3  

Continental crust generally underlies the continents and the continental shelves.

Oceanic crust generally underlies the abyssal plains and continental rise.  Small, deformed pieces of oceanic crust can be obducted on land to create ophiolites.

Transitional crust typically occurs under the continental slope. 

Isostasy and these crustal variations lead to the features at passive continental margins.

Last revision 8/24/2016