Sea Floor Magnetism

The field behaves as if a permanent magnet were located near the center of the earth.

Sea floor magnetism. A test of the hypothesis of sea floor spreading was provided by studies of the earth s magnetism. If the oceanic crust reaches a deep sea trench it sinks into the trench and is lost into the mantle. Looking at the magnetism of the seafloor scientists discovered something astonishing. Basalt the once molten rock that makes up most new oceanic crust is a fairly magnetic substance and scientists began using magnetometers to measure the magnetism of the ocean floor in the 1950s what they discovered was that the magnetism of the ocean floor around.

As oceanic crust forms and spreads moving away from the ridge crest it pushes the continent away from the ridge axis. Warships also carried magnetometers. Seafloor lavas have built in magnetic clocks that reveal their age. The earth s magnetic field the earth s magnetic field is thought to arise from the movement of liquid iron in the outer core as the planet rotates.

The magnetic stripes continue across the seafloor. Like the echo sounders the magnetometers were used to search for submarines. When seafloor lava solidifies at the seafloor its magnetic crystals are quenched in alignment with earth s magnetic field and the rocks magnetic polarity is preserved. In the mid 1960s evidence of magnetic stripes on the seafloor convinced the geologic community of the validity of plate tectonics theory and it is often pointed to today as clinching evidence for the theory.