Flexi Says: World War II allowed scientists to make some puzzling observations. The observations came from seafloor bathymetry and magnetism. These observations are: The seafloor has a large mountain range running through it. Deep trenches are found far from the ridges. Guyots have eroded tops that are deep below sea level.
The magnetic polarity of the seafloor changes. The center of the ridge is of normal polarity. Stripes of normal and reverse polarity are found symmetrical on both sides of the ridge. The youngest seafloor is at the ridge. The oldest is farthest from the ridge. The oldest seafloor is much younger than the oldest continent. Scientists needed to explain these observations. After the war, Harry Hess put together the ideas and evidence he needed. Hess resurrected Wegener's continental drift hypothesis. He reviewed the mantle convection idea. He thought about the bathymetric features and the patterns of magnetic polarity on the seafloor. In 1962, Hess published a new idea that he called seafloor spreading. Hess wrote that hot magma rises up into the rift valley at the mid-ocean ridges. The lava cools to form new seafloor. Later more lava erupts at the ridge. The new lava pushes the seafloor horizontally away from the ridge axis. Seafloor spreading is the mechanism that Wegener was looking for! Convection currents within the mantle drive the continents. The continents are pushed by oceanic crust like they are on a conveyor belt.
