Isostasy: Why some rocks Float Higher Than Others a The continents average about 4.5 km elevation above the ocean floor They stand notably higher than the ocean basins because the thick continental crust is relatively light(average density 2.7 g/cm3) a The thin oceanic crust is relatively heavy (average density 3.0g/cm) he lithosphere floats on the asthenosphere.Isostasy: Why Some Rocks Float Higher Than Others ◼ The continents average about 4.5 km elevation above the ocean floor. ◼ They stand notably higher than the ocean basins because the thick continental crust is relatively light (average density 2.7 g/cm3 ). ◼ The thin oceanic crust is relatively heavy (average density 3.0g/cm3 ). ◼ The lithosphere floats on the asthenosphere