Geological structure and relief of the ocean floor
The ocean floor consists of large lithosphere plates; most of them form single plates together with continents and so are named after the continents, and only the Pacific floor is an independent plate. The floor is covered with sediments: near the coast terrigenous deposits carried from land (about 25 % of the ocean area), in deeper parts ooze formed from organism remains, and at depths over 5 000 m red deep-sea clay (about 36 %). The relief forms are the continental shelf (to 200 m), the continental slope, the continental foot, ocean basins, mid-ocean ridges and the deepest trenches. Mid-ocean ridges cross all the oceans, with a total length over 60 thousand km (modern estimates about 65 thousand km). The deepest place is the Mariana Trench in the Pacific (about 10 935 m). The ocean floor is the thin, 5–10 km, part of the crust. Five drainage basins are shown on the map: Pacific, Atlantic, Indian, Arctic and closed basins; a river belongs to the basin of the ocean it flows into.
“Ocean floor profile”: make a cross-section of the ocean floor from cardboard or plasticine, label the shelf, slope, plain, ridge and trench and write their depths.