The Crust Under The Ocean Floor

As upwelling of magma continues the plates continue to diverge a process known as seafloor spreading.

The crust under the ocean floor.

Oceanic crust is born at the mid ocean ridges where plates are pulled apart. It is light and brittle and can break. Magma oozes up from the mantle through a crack in the ocean floor filling in the space between the plates and spreading out from the plate boundary. It is composed of several layers not including the overlying sediment.

The crust thickness averages about 18 miles 30 kilometers under the continents but is only about 3 miles 5 kilometers under the oceans. The oldest existing oceanic crust is in the ionian sea part of the eastern mediterranean basin. The oceanic crust displays a pattern of magnetic lines parallel to the ocean ridges frozen in the basalt. The destruction of oceanic crust occurs at subduction zones where oceanic crust is forced under either continental crust or oceanic crust.

A symmetrical pattern of positive and negative magnetic lines emanates from the mid ocean ridge. The continental crust covers only one third of the earth s surface and makes up all of the dry land found on earth. New rock is formed by magma at the mid ocean ridges and the ocean floor spreads out from this point. Oceanic crust is about 6 km 4 miles thick.

The oldest parts of continental crust on the other hand are more than 4 billion years old. Largely due to subduction oceanic crust is much much younger than continental crust. Everything older has been pulled underneath the continents by subduction. Oceanic crust the outermost layer of earth s lithosphere that is found under the oceans and formed at spreading centres on oceanic ridges which occur at divergent plate boundaries.

Structure of the earth. Subduction zone the place where one plate is getting bent and pulled under the edge of another plate. Plate tectonics plate tectonics seafloor spreading. Oceanic crust is thin and young no more than about 20 km thick and no older than about 180 million years.

Continental crust earth. Two types of crust make up the land on earth and its ocean floor. Today the atlantic basin is actively spreading at the mid atlantic ridge. These age data also allow the rate of seafloor spreading to be.

The seafloor of the ionian sea is about 270 million years old. Only a small portion of the oceanic crust produced in the atlantic is subducted. Samples collected from the ocean floor show that the age of oceanic crust increases with distance from the spreading centre important evidence in favour of this process.