Oceanic crust  From Wikipedia, the free encyclopedia Jump to:
navigation, search Colors indicate the age of oceanic
lithosphere, wherein red indicates the youngest age, and blue
indicates the oldest age. The lines represent tectonic plates.
Oceanic crust is the part of Earth's lithosphere that surfaces
in the ocean basins. Oceanic crust is primarily composed of
mafic rocks, or sima, which is rich in iron and magnesium. It is
thinner than continental crust, or sial, generally less than 10
kilometers thick; however it is denser, having a mean density of
about 2.9 grams per cubic centimeter[1] as opposed to
continental crust which has a density of about 2.7 grams per
cubic centimeter.[2]       Life cycle[edit]   As the mantle
rises it cools and melts, as the pressure decreases and it
crosses the solidus. The amount of melt produced depends only on
the temperature of the mantle as it rises. Hence most oceanic
crust is the same thickness (7±1 km). Very slow spreading ridges
(<1 cm·yr−1 half-rate) produce thinner