Magnetic stripes on the seafloor are caused in part by: A. declination of the poles. B. tidal forces. C. movement of ocean crust. D. gravity.
The Correct Answer and Explanation is:
Correct Answer: C. movement of ocean crust
Magnetic stripes on the seafloor are caused in part by the movement of oceanic crust, which plays a central role in the process of seafloor spreading. These stripes are symmetrical patterns of magnetic anomalies that run parallel to mid-ocean ridges. They provide key evidence for the theory of plate tectonics and the dynamic nature of Earth’s lithosphere.
As magma rises from the mantle at mid-ocean ridges, it cools and solidifies to form new oceanic crust. During the cooling process, magnetic minerals, particularly magnetite, within the basaltic rock align with Earth’s magnetic field. Over time, Earth’s magnetic field has reversed many times, switching between periods of normal polarity (where magnetic north is near the North Pole) and reversed polarity (where magnetic north is near the South Pole).
Because of this, as new crust continuously forms at the ridges and moves outward on both sides, it captures a record of the Earth’s magnetic field at the time of its formation. This results in a pattern of alternating magnetic stripes—some matching the current magnetic polarity and others showing reversed polarity. These stripes mirror each other on either side of the mid-ocean ridge, indicating that new crust is being added symmetrically due to divergent plate boundaries.
The study of these magnetic patterns, known as paleomagnetism, has been crucial in confirming the mechanism of seafloor spreading proposed by Harry Hess in the 1960s. It also supports the broader theory of plate tectonics, explaining how continents drift and oceans expand over geologic time. Thus, the magnetic stripes are not random but are a chronological record of Earth’s magnetic history and a direct result of the continuous movement of oceanic crust.
