What is the supportive evidence that sea floor spreading does exist?
The evidence exists in the extrusive igneous rock, basalt, on the ocean floor near the mid-oceanic ridges. The magnetic orientation of the Earth is recorded in the igneous rock at the time of its formation. The orientation of Earth’s magnetic field changes over time, and thus provides a way to relatively date rocks. These orientations can be recorded and mapped with the aid of a magnetometer. Magnetic orientation of oceanic crustal rocks on one side of the mid-oceanic ridge appear as mirror images to the magnetic orientation of oceanic crustal rocks on the other side, meaning that the seafloor is spreading in opposite directions from the rift zone over time. Modern instruments have measured the movement of crust away from the rift zone and it roughly approximates the rate of human fingernail growth.
