Which feature on the ocean floor provides evidence for plate tectonics?

Which feature on the ocean floor provides evidence for plate tectonics?

• A. Fossil records
• B. Magnetic reversals recorded in rocks
• C. Coral reefs
• D. Deep trenches at one location

Answer: (B)

Magnetism recorded in rocks on the ocean floor provides strong evidence for plate tectonics. When magma at mid-ocean ridges cools and solidifies, it preserves the Earth's magnetic field direction at that moment. Over geological time, the field has reversed many times, so rocks lock in either normal or reversed polarity. As new magma keeps rising at these ridges and pushes old crust outward, a pattern of magnetic stripes forms on both sides of the ridge, mirroring each other. This symmetrical arrangement of normal and reversed magnetic zones matches the idea that new crust is being created at ridges and the plates are moving apart, then being recycled at trenches. This direct, historical record from the ocean floor spatially ties the motion of lithospheric plates to changes in Earth's magnetic field, making it the strongest, most specific evidence for plate tectonics. Fossil records do support the idea that continents were once joined, since similar fossils are found on now-separate landmasses, but they’re not a feature on the ocean floor itself that demonstrates ongoing movement. Coral reefs indicate shallow, warm waters and can inform past climate and sea levels, not plate-motion processes. Deep trenches at one location point to subduction, which is part of plate tectonics, but observing a single trench doesn’t demonstrate the global pattern and mechanism of plate movement that the magnetic record reveals.

Magnetism recorded in rocks on the ocean floor provides strong evidence for plate tectonics. When magma at mid-ocean ridges cools and solidifies, it preserves the Earth's magnetic field direction at that moment. Over geological time, the field has reversed many times, so rocks lock in either normal or reversed polarity. As new magma keeps rising at these ridges and pushes old crust outward, a pattern of magnetic stripes forms on both sides of the ridge, mirroring each other. This symmetrical arrangement of normal and reversed magnetic zones matches the idea that new crust is being created at ridges and the plates are moving apart, then being recycled at trenches. This direct, historical record from the ocean floor spatially ties the motion of lithospheric plates to changes in Earth's magnetic field, making it the strongest, most specific evidence for plate tectonics.

Fossil records do support the idea that continents were once joined, since similar fossils are found on now-separate landmasses, but they’re not a feature on the ocean floor itself that demonstrates ongoing movement. Coral reefs indicate shallow, warm waters and can inform past climate and sea levels, not plate-motion processes. Deep trenches at one location point to subduction, which is part of plate tectonics, but observing a single trench doesn’t demonstrate the global pattern and mechanism of plate movement that the magnetic record reveals.