How are ocean basins formed?

• A. By spreading of the seafloor due to tectonic plates splitting apart, creating basalt oceanic crust and continental granite crust.
• B. By river erosion carving basins.
• C. By meteor impacts creating circular basins.
• D. By volcanic lava pooling on land.

Answer: (A)

Ocean basins form mainly through plate tectonics. When tectonic plates pull apart at divergent boundaries, magma rises into the gap and solidifies as new oceanic crust, which is predominantly basalt. As spreading continues, more space opens up and seawater fills the area, creating a large ocean basin between the separating plates. The crust that forms near these basins is oceanic basalt, while the surrounding continents are underlain by granitic crust. This combination—spreading seafloor and the contrasting crust types—explains how ocean basins develop.