A comparison of the elevation differences between the seafloor and land is given in the hypsographic curve.
Oceanic crust consists mainly of basaltic rock with an thin veneer of sediment.
Where exposed, the top of the basaltic rock consists of pillow lavas . Sediment is generally thickest near the continental margins where the ocean's crust is oldest and very thin to absent near the midocean ridge where the crust is youngest. In addition to sand, silt and clay from the continents, ocean sediment consists of organic remains and chemical precipitates of both organic and inorganic origin. The organic precipitates include siliceous ooze and calcareous ooze that consist of the skeletal remains of small planktonic organisms. The inorganic chemical precipitates include manganese nodules .