Magnetic stripes on the seafloor are caused in part by:
A. tidal forces.
B. gravity.
C. movement of ocean crust.
D. declination of the poles.
The correct answer and explanation is:
The correct answer is C. movement of ocean crust.
Magnetic stripes on the seafloor are primarily caused by the movement of oceanic crust due to seafloor spreading. These stripes are a result of the Earth’s magnetic field periodically reversing, a phenomenon known as geomagnetic reversal. The Earth’s magnetic field flips, so the magnetic north and south poles switch places. This reversal happens irregularly but with a distinct pattern over geological time scales.
When the oceanic crust forms at mid-ocean ridges, magma rises to the surface and cools, solidifying into rock. As the magma cools, iron-rich minerals within the rock align with the Earth’s magnetic field. If the magnetic field is in a certain orientation at the time of cooling, the minerals will align in that direction. When the magnetic field reverses, the minerals will align in the opposite direction. This creates alternating bands of magnetized rock, with stripes of normal and reversed polarity parallel to the mid-ocean ridges.
As the oceanic plates move away from the ridge due to seafloor spreading, these magnetic stripes get preserved in the crust. Over millions of years, the movement of the crust spreads these bands farther apart. The alternating stripes are symmetrical on either side of the ridge, providing strong evidence for the theory of plate tectonics and seafloor spreading.
Tidal forces (A), gravity (B), and declination of the poles (D) do not significantly contribute to the formation of these magnetic stripes. The process of seafloor spreading and geomagnetic reversal, driven by the movement of the ocean crust, is the primary cause. This evidence has been crucial in confirming that continents and ocean basins are dynamic and constantly changing over time.