At the mid-ocean ridges, lava is pushing the sea floor away from the ridge on each side. Eventually that part of the seafloor will be subducted under a continental plate at a convergent boundary. That means that the seafloor is constantly being renewed. The newest rocks will be found closest to the mid-ocean ridge and the oldest the greatest distance from the mid-ocean ridge.
The oldest rock found beneath the ocean dates back only about 200 million years.
However, the rock underlying the continents is as much as four billion years old.
