The expansion of the ocean floor
Hess postulated, in the early 1960s, the hypothesis of the expansion of the ocean floor. He claimed that the earth's crust was forming in the ridges and that it should be disappearing elsewhere. He suggested that the newly created oceanic crust was moving away from the ridges, and that millions of years later, it would descend into the ocean trenches. According to Hess, the Atlantic Ocean was expanding while the Pacific Ocean was shrinking.
For this reason also, the thickness of marine sediments is greater in areas far from the ridge, since they have had more time to settle.
This, coupled with evidence of symmetrical magnetic bands on either side of the ridges indicating magnetic inversions, would support the idea that the newer crust is closer to the ridge and the older crust further away.
Therefore, as proposed by Hess, the oceanic crust is formed in the oceanic ridges from materials from the mantle and would accumulate on both sides of the ridge, growing the oceanic crust. The destruction of said crust would take place in the oceanic trenches, where subduction takes place, introducing the crust inside the Earth.