Final answer:
Alternating magnetic bands on the sea floor confirm sea floor spreading by showing a record of Earth's historical magnetic field reversals.
Step-by-step explanation:
The alternating bands of magnetic material found in the sea floor that exhibit magnetic reversal provide essential evidence for the theory of sea floor spreading. This phenomenon occurs because, as magma rises at the mid-ocean ridges due to tectonic activity, it cools and solidifies, recording the Earth's magnetic field at the time of its formation. As Earth's magnetic field has reversed polarity many times over geological history, these rocks show a pattern of magnetic stripes with alternating normal and reversed polarity, paralleling the ridge. By studying the patterns of these magnetic stripes and the rate at which the sea floor spreads apart, scientists can infer a timeline of Earth's magnetic reversals, thereby gaining insights into the history of our planet's magnetic field.