Final answer:
Newly formed oceanic crust at spreading centers captures Earth's current magnetic polarity, allowing scientists to use spreading rates and magnetic striping to date geological events and the seafloor itself.
Step-by-step explanation:
The newly erupted oceanic crust that emerges from spreading centers records Earth's magnetic polarity from the present period. This is because as the seafloor spreads and new crust is formed, it captures the current orientation of the Earth's magnetic field. This magnetic record, termed 'magnetic striping', reveals patterns of magnetic reversals over geologic time when investigated relative to the distance from mid-ocean ridges. Magnetic reversals are changes in Earth's magnetic field that periodically switch the positions of magnetic north and magnetic south.
By using the average spreading rate of the mid-Atlantic Ridge, around 4 cm per year, scientists can effectively date the oceanic crust. Knowledge of the spreading rate in conjunction with magnetic striping allows for the determination of a geological record of Earth's magnetic field.