Which is a main surface feature on Earth formed by plate tectonics?

• A. Island chains
• B. Mid-ocean ridges
• C. Continents
• D. Shelves

Answer: (B)

Plate tectonics creates new crust at divergent boundaries, and the most conspicuous surface expression of this process is the mid-ocean ridge. As two tectonic plates pull apart, mantle rock rises, partially melts, and erupts as magma to form fresh oceanic crust. This continuous seafloor spreading lifts up a vast, continuous underwater mountain range—the mid-ocean ridges—that winds through all the world’s oceans. They define the map of the seafloor and mark areal boundaries where new crust is constantly being created, which is a direct and ongoing result of plate tectonic activity.

Island chains arise from volcanic activity associated with specific tectonic settings (subduction zones or volcanic hotspots) and aren’t the global, primary surface feature formed by plate tectonics. Continents and shelves are major crustal features, but they’re large-scale landmasses or continental margins rather than the ongoing, tectonically driven surface feature that characterizes Earth’s ocean floors.