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Why is the oldest known ocean floor only about 200 million years old?

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World map highlighting major features of the ocean basins, including trenches, ridges, basins, and plateaus labeled throughout the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. Continents are shown with shaded terrain, and prominent undersea features such as the Mid-Atlantic Ridge, Mariana Trench, and Kerguelen Plateau are marked across the map. — ocean basin Major features of the ocean basins.

The oldest known ocean floor is approximately 200 million years old because the Earth’s oceanic crust is continuously recycled through the process of plate tectonics.1

While new seafloor is constantly generated at mid-oceanic ridges through seafloor spreading, older, denser oceanic crust is eventually consumed at subduction zones, where it is dragged back into the Earth's mantle. Because this cycle of creation and destruction is ongoing, the vast majority of the ocean floor is geologically young compared to the continental crust, which is much more buoyant and does not subduct in the same way.123

The current phase of ocean basin development is linked to the breakup of the supercontinent Pangea, which began just under 200 million years ago. Consequently, the oldest preserved segments of seafloor—found in areas like the western equatorial Pacific—date back to this period of rifting.1