This is the outermost layer of the earth. It contains two segments, the oceanic crust and continental crust. These are the surface of the Earth, such as it is the coldest part of our planet, because cold rocks deform slowly. The crust (whether continental or oceanic) is the thin layer of distinctive chemical composition overlying the ultramafic upper mantle. The base of the crust is defined seismologically by the Mohorovicic discontinuity. Oceanic and continental crust are formed by entirely different geological processes.
The oceanic crust contains 0.099 % of the Earth's mass. This oceanic crust have simple history about 200 million years. The oceanic crust average 7 kilometers in thickness, varying from 5 to 8 kilometers or this is the 3-6 miles thick. It is made up of basaltic and the contains the oceans and water. Basaltic is more than 50% silicon oxygen 2, dense (density>3) and young (<250My) and is rich in iron and magnesium. The oceanic crust contains 0.147 % of the mantle-crust mass. The oceanic ridge system, a 40,000 kilometer (25,000 mile) network of volcanoes, generate new oceanic crust at the rate of 17 km 3 per year, covering the ocean floor with basalt. Hawaii and Iceland are two examples of the accumulation of basalt piles. The majority of the Earth's crust was made through volcanic activity. I got this source of information from University of Colorado (Joe Smyth's)
CHARACTERISTICS OF OCEANIC CRUST AND CONTINENTAL CRUST
|AVERAGE THICKNESS||7 km||30 to 50 km|
|DENSITY||3.0 gm/cm3||2.7 gm/cm3|
|COMPOSITION||basalt underlain by gabbro||granite, other plutonic rocks, schist, gneiss|
|MANTLE CRUST MASS||0.147%||0.554%|
The continental crust contains 0.374 % of the Earth's mass. This continental crust have much more complex history than oceanic crust which is 4 billion years. Continental crust is much thicker than crust, averaging 30 to 50 kilometers in thickness, though it varies from 10 to 70 kilometers which is18-25 miles thick. It is made up of granite and contains the land masses. Granitic is less than 60 % silicon oxygen 2, light (density <2.85), and old (250-3700 Myrs). The continental crust contains 0.554 % of the mantle-crust mass. This is the outer part of the Earth composed essentially of crystalline rock. These are low density buoyant minerals dominated mostly by quartz and feldspars. This source of information came from (http://spaceart.com/solar/eng/earthint.htm)