Seafloor spreading

Seafloor spreading is the slow lateral deviation ( engl. spreading ) of the ocean floor as part of the process of mantle convection. The ocean floor is made of thousands of kilometers of large plates that float on the softer mantle. Is located at the seam between the plates a spread zone with thin, newly formed oceanic crust over a flat magma chamber. The spreading zone and the still warm plate margins rise by buoyancy ( isostasy ) to a mountain range. These so-called mid-ocean ridges form a worldwide, tens of thousands of kilometers long network diverse volcanic activity.

The magma is produced by pressure relief from the hot material in the mantle. It fills from below the centimeter- wide cracks that occur sporadically through the spread, and also forms on the surface of a layer of pillow. Upon cooling, the orientation of the geomagnetic field is stored in the lava rock. The frequent in geological time change of the earth's magnetic field lead to a symmetrical banding in the magnetization of the disk surface. Pillow lava and magnetic banding were discovered from the early 1960s with research vessels, which the hypothesis of continental drift to break through.

The spreading rate is the vertical component ( transverse to the weld ) the difference between the drift velocities of the two disks. For example, the Atlantic Ocean widened by 2 cm a year and is about 130 million years old.

A drive of spread is the descent of oceanic crust into the mantle ( subduction ) after it is usually cooled many 10 million years.

Determine the age of the ocean floor

During cooling of the lava magnetizable minerals align according to the magnetic field of the earth. Individual rock strips are oriented to the north or south, which is due to the recurring reversals of the magnetic field of the earth. The magnetic orientation of each rock strip can be assigned to a specific time. The further away from the back of strip rock are older and on both sides of the back equidistant rock strip detectable same age. So you can compare the age determination of the seabed with the determination of the age of a tree by annual rings.