Which feature is commonly used as evidence for plate tectonics?

Which feature is commonly used as evidence for plate tectonics?

• A. Fossil distribution
• B. Lunar cycles
• C. Ocean salinity
• D. Magnetic polarity of ocean rocks

Answer: (D)

The main concept being tested is how the ocean floor records Earth’s magnetic field to reveal plate movements. As magma erupts at mid-ocean ridges and cools into rock, magnetic minerals lock in the direction of the current magnetic field. Over time, as the plates move apart, new rock forms and pushes older rock outward, preserving a history of magnetic polarity reversals. When the field flips, rocks formed after that flip capture the opposite polarity. This results in clear, alternating stripes of normal and reversed polarity on both sides of the ridges that line up with the timing of reversals and the spreading rate. That pattern provides strong, direct evidence that the sea floor—and the continents riding on it—is moving. Fossil distribution can suggest past connections between continents, but it doesn’t provide the same time-resolved record of seafloor spreading, while lunar cycles and ocean salinity aren’t tied to crustal movement in the same way.

The main concept being tested is how the ocean floor records Earth’s magnetic field to reveal plate movements. As magma erupts at mid-ocean ridges and cools into rock, magnetic minerals lock in the direction of the current magnetic field. Over time, as the plates move apart, new rock forms and pushes older rock outward, preserving a history of magnetic polarity reversals. When the field flips, rocks formed after that flip capture the opposite polarity. This results in clear, alternating stripes of normal and reversed polarity on both sides of the ridges that line up with the timing of reversals and the spreading rate. That pattern provides strong, direct evidence that the sea floor—and the continents riding on it—is moving. Fossil distribution can suggest past connections between continents, but it doesn’t provide the same time-resolved record of seafloor spreading, while lunar cycles and ocean salinity aren’t tied to crustal movement in the same way.