Another part of tectonic theory, which came before the suggestion of plates, is palaeomagnetism which was first discovered in the 1960s. It was suggested that approximately 400,000 years the Earth experienced reverse polarity. This means that the magnetic north and south poles swap direction. This was backed up by evidence which involved ferrous rich rocks such as magnetite under the Atlantic Ocean. These rocks are found on the sea floor on either side of the Mid-Atlantic Ridge and are formed when solidified magma broke through the lithosphere at the Mid-Atlantic Ridge
Another part of tectonic theory, which came before the suggestion of plates, is palaeomagnetism which was first discovered in the 1960s. It was suggested that approximately 400,000 years the Earth experienced reverse polarity. This means that the magnetic north and south poles swap direction. This was backed up by evidence which involved ferrous rich rocks such as magnetite under the Atlantic Ocean. These rocks are found on the sea floor on either side of the Mid-Atlantic Ridge and are formed when solidified magma broke through the lithosphere at the Mid-Atlantic Ridge