Final answer:
The thickness of the lithosphere decreases when moving from an oceanic ridge to an oceanic trench.
Step-by-step explanation:
When moving from an oceanic ridge to an oceanic trench, the thickness of the lithosphere decreases.
The lithosphere is the rigid outer layer of the Earth's crust and upper mantle. It consists of the crust and the uppermost part of the mantle, and it is broken into tectonic plates. At oceanic ridges, new crust is formed through volcanic activity and spreads apart, creating a new lithosphere. As the lithosphere moves away from the ridge and towards an oceanic trench, it becomes older and denser. When it reaches a trench, it can be subducted or forced beneath another plate, leading to its destruction. This subduction process causes the lithosphere to become thinner as it sinks into the mantle.