Part 1 of Essay
A trench is any long, narrow, steep-sided depression in the ocean bottom. The deepest known depression of this kind is the Mariana Trench, which lies east of the Mariana Islands in the western North Pacific Ocean . Of the Earth's 20 major trenches, 17 are found in the Pacific. The only Atlantic trenches are the Puerto Rico ....

Part 2 of Essay
.... graded layers are found in the trench. Large amounts of remains cannot build up because they either are dragged into the Earth's interior or are distorted into folded masses and molded into new material of the continents. Deep trench in the sea bed indicating the presence of a destructive margin (produced by the movements of plate tectonics). The dragging downwards of one plate of the lithosphere beneath another means that the ocean floor is pulled down. Ocean trenches are found around the edge of the Paci ....