Where is new oceanic crust formed?

• A. At mid-ocean ridges where divergent boundaries occur.
• B. At subduction zones where crust sinks.
• C. In continental interiors at hotspots exclusively.
• D. At the Earth's core-mantle boundary.

Answer: (A)

New oceanic crust forms at mid-ocean ridges, where divergent boundaries exist. As tectonic plates pull apart, mantle material rises to fill the gap and erupts as magma. When this magma cools and solidifies, it becomes basaltic oceanic crust. As spreading continues, new crust is created at the ridge and slowly moves away on both sides, making the newest crust closest to the ridge and the oldest farther away. This process, sea-floor spreading, also explains the symmetric ages of seafloor rocks and the magnetic striping pattern recorded in the rocks.

Subduction zones recycle crust by sinking old oceanic crust back into the mantle, rather than creating new crust. Hotspots under oceans can produce volcanic activity, but they don’t generate new oceanic crust in the same regular, symmetrical way as mid-ocean ridges. The core–mantle boundary is deep inside Earth and not the site where new surface crust forms.