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Why are ocean-floor rocks generally younger than continental rocks?

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continental landform Davis's proposed landscape-development states. The morphology shown is not actually time-indicative. For example, A could be a gully system in soft sediment or a canyon such as the Royal Gorge in Colorado, which is millions of years old. The ridge-ravine topography of B would normally develop under humid conditions, but the river meandering on alluvium indicates a prior or extraneous non-humid aggrading mechanism. The riverine plain of C implies a complex history of planation and aggradation in a current fluvial mode.

Ocean-floor rocks are generally much younger than continental rocks because of the continuous cycle of creation and destruction inherent in plate tectonics.

Oceanic crust is constantly formed at spreading centres along oceanic ridges as magma rises and cools. Because this crust is dense, it eventually cools further and becomes even heavier, leading it to subduct back into the Earth's mantle at deep-sea trenches. This process ensures that oceanic crust is transient, with a mean age of approximately 60 million years and rarely exceeding 200 million years.1234

In contrast, continental crust is composed of lighter, more buoyant material that resists subduction. Because it is not recycled into the mantle in the same way as oceanic crust, it is preserved over billions of years. Consequently, while the ocean floor is geologically young, the oldest continental rocks have been dated to more than 4 billion years old.534