Question

Which of the following processes is/are responsible for the alternate bands of magnetic polarity observed in seafloor basalts?

• A. Convection in the mantle
• B. Convection in the outer core
• C. Convection in the inner core
• D. Seismicity at mid-oceanic ridges

Hint:

Magnetic polarity reversals are recorded in seafloor basalts as they cool at mid-ocean ridges. The Earth's outer core, where convection occurs, is responsible for generating the magnetic field.

Answer 1

The Correct Option is B

Step 1: Understanding magnetic polarity and seafloor basalts.
The alternate bands of magnetic polarity observed in seafloor basalts are a result of magnetic reversals. These reversals occur when the Earth's magnetic field flips, with the magnetic north and south poles switching places.
The seafloor basalts record these changes as they form at mid-ocean ridges, with newly formed lava aligning with the current magnetic field.
As the lava cools and solidifies, it "locks in" the magnetic polarity at the time of solidification, creating alternating bands of normal and reversed polarity.

Step 2: Identifying the source of magnetic field reversals.
The Earth's magnetic field is generated by the outer core, where convective motion in the liquid iron and nickel creates electric currents, which in turn generate the magnetic field.
This convective motion in the outer core is responsible for the magnetic field reversals recorded in the seafloor basalts.
- Option (A): Convection in the mantle: While the mantle does influence tectonic processes, it is not directly responsible for generating the magnetic field or its reversals. Thus, this option is incorrect.
- Option (B): Convection in the outer core: This is the correct answer. Convection in the outer core generates the Earth's magnetic field, and changes in this field result in magnetic reversals recorded in seafloor basalts.
- Option (C): Convection in the inner core: The inner core is solid and does not directly contribute to the generation of the Earth's magnetic field or its reversals.
- Option (D): Seismicity at mid-oceanic ridges: Seismicity at mid-ocean ridges is related to tectonic activity, not to the magnetic reversals observed in seafloor basalts. Therefore, this option is incorrect.

Step 3: Conclusion.
The process responsible for the alternate bands of magnetic polarity observed in seafloor basalts is convection in the outer core. Hence, the correct answer is (B).
\[ \boxed{\text{Convection in the outer core}} \]