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What did Harry H. Hess propose about seafloor spreading in 1960?

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oceanic ridge Major features of the ocean basins.

In 1960, Harry H. Hess proposed a model of seafloor spreading that provided a global explanation for tectonic features. Drawing on the concept of convective flow in the mantle, Hess suggested that oceanic ridges are the surface expressions of rising, diverging mantle material.12

According to this model:
* New oceanic crust is continuously generated at ridge crests as molten material wells up and cools.12
* This crust is carried laterally away from the ridges, causing the ocean floor to spread and the continents to drift apart.12
* The crust eventually cools, subsides, and is destroyed as it descends into deep-sea trenches and reenters the mantle.12

This hypothesis explained why the age of the oceanic crust increases with distance from the ridges and why no oceanic rocks older than 200 million years are found, as the seafloor is constantly being recycled. This work was foundational to the development of plate tectonics.12