Palaeomagnetism

• In the 1960s, Cold War technology, designed to track enemy submarines, measured tiny variations in the Earth‘s magnetic field
• When mapped by geologists, Vine and Matthew, this data revealed a stripped pattern across the ocean floor, on the Reykjanes mid ocean ridge near Iceland - this evidence was published in 1963
• When lave erupts along the mid-ocean ridge, the lava contains magnetite minerals, and aligns itself with the earths magnetic field - as the lava cools, the orientation of the iron particles are locked in place
• Every 450,000 years the polarity of earths magnetic field reserves, and the width of each strip on the sea floor is proportional to the time scale of each magnetic reversal
• The symmetrical pattern therefore shows that oceanic lithosphere is diverging along the plate boundary