Final answer:
The finding of bands with alternating magnetic orientation near oceanic ridges supports the concept of seafloor spreading and provides a historical record of Earth's magnetic field reversals, offering insights into the rate at which tectonic plates move apart.
Step-by-step explanation:
Discovering bands of different magnetic orientations parallel to the oceanic ridges was decisive as it provided evidence for the theory of seafloor spreading and helped explain the process of continental drift. This magnetic striping pattern, resulting from volcanic activity along the mid-Atlantic ridge, suggests that the Earth's magnetic field has reversed its polarity repeatedly over geologic time. As fresh magma extrudes onto the ocean floor and cools, it records the current orientation of Earth's magnetic field. When the magnetic poles reverse, this is mirrored in the magnetization of the newly formed rocks, creating a symmetrical pattern of magnetic stripes on either side of the ridge. By calculating the spreading rate of the seafloor, scientists can determine the rate at which tectonic plates are moving apart and use this data to establish a timeline for the reversals of the magnetic field — a historical record of Earth's paleomagnetism.