The formation of Earth's deepest ocean trench is primarily due to the process of subduction, which occurs when a denser tectonic plate converges with a lighter plate. In this scenario, the denser oceanic plate is forced beneath the lighter continental or oceanic plate, leading to the creation of a deep trench in the ocean floor.
Therefore, the correct explanation is:
A denser plate converged with a lighter plate.
This subduction process is responsible for forming major ocean trenches, like the Mariana Trench, which is the deepest part of the world's oceans.