What process describes the creation of new ocean floor as tectonic plates move apart?

• A. Subduction
• B. Seafloor spreading
• C. Mantle plumes
• D. Weathering

Answer: (B)

When tectonic plates move apart at mid-ocean ridges, magma from the mantle rises into the gap, erupts along the ridge, and then solidifies to form new oceanic crust. As the plates continue to separate, this newly formed crust pushes away from the ridge on both sides, creating fresh sea floor. This process—upwelling mantle magma filling the widening gap and solidifying to birth new crust—is what drives seafloor spreading. It also explains why ocean floors get younger closer to the ridges and older farther away, and why magnetic stripes appear as the rocks record reversals in Earth’s magnetic field.

Subduction involves one plate sinking beneath another, recycling crust rather than creating new crust. Mantle plumes lead to volcanic activity hotspots (often not at plate boundaries) and don’t describe the steady creation of ocean floor along spreading centers. Weathering is the breakdown of rocks at the surface and does not generate new oceanic crust.