4. Structure of Ocean Floor

• (i) There is land under water
• (ii) There are volcanoes under water
• (iii) Land is continuous and there is water in deeper parts.
• ✓ (iv) Though land is continuous, its level is not the same everywhere like that of water

Answer: Though land is continuous, its level is not the same everywhere like that of water

• ✓ (i) Continental shelf
• (ii) Continental slope
• (iii) Abyssal plains
• (iv) Marine deeps

Answer: Continental shelf

• ✓ (i) Rivers, glaciers, remains of plants and animals
• (ii) Volcanic ash, continental shelf, remains of plants and animals
• (iii) Volcanic ash, lava, fine particles of soil
• (iv) Volcanic ash, remains of plants and animals, abyssal plains

Answer: Rivers, glaciers, remains of plants and animals

Marine Trenches, Abyssal Plains, and the marine oozes/deposits found on the ocean bed are highly useful for deep sea research. They help scientists understand the age of the ocean floor, the availability of minerals, and the unique marine life existing at great depths.

Marine Islands and the Continental Shelf are the most appropriate landforms for protecting marine borders and building naval bases due to their proximity to the surface and strategic locations.

• The ocean floor contains vital marine deposits and oozes that help us understand prehistoric marine life and the age of the earth.
• The continental shelf provides extensive fishing grounds that sustain human food requirements.
• It is a rich source of economically important minerals, natural gas, and mineral oil (e.g., Mumbai High).
• Studying the active areas of the ocean floor helps in predicting earthquakes and tsunamis, thereby protecting coastal regions.

The continental shelf is the shallowest part of the ocean bed (extending up to a depth of roughly 200 meters). Because it is shallow, sunlight easily reaches the sea bed. This encourages the abundant growth of algae, plankton, and other marine vegetation. Since these microorganisms serve as the primary food for fish, millions of fish gather and breed in this region, making the continental shelf an absolute paradise for large-scale fishing activity.

The ocean bed is not perfectly flat; it consists of massive submerged hills, plateaus, and mountain ranges that are hundreds of kilometers wide and thousands of kilometers long. When the structural peaks of these towering submerged mountains rise above the sea level, they become visible to us. Surrounded by water on all sides, these exposed summits form what we call marine islands (e.g., the Andaman and Nicobar Islands).

Starting from the coast, the land gently extends under the sea as the continental shelf. Once the extent of the shallow shelf is over, the sea bed suddenly drops, and the slope becomes extremely steep. This steeply inclined region is the continental slope. Beyond this slope lie the deep abyssal plains and the true, deep ocean basin. Because it clearly marks the end of the shallower continental crust and the beginning of the deep ocean floor, its lower boundary is considered the boundary of the continents.

Humans routinely dump immense quantities of hazardous, human-induced materials into the oceans, including sewage, solid waste, radioactive materials, waste chemicals, and plastics. Most of these materials are highly toxic and non-perishable (non-biodegradable). They severely contaminate the sea water, suffocate aquatic animals, and destroy delicate coral reefs. Since the biodiversity found in seas and oceans is actually much higher than on land, this pollution poses an irreversible threat to the entire marine ecosystem and the global environment.

Answer: Marine Islands

Answer: Madagascar is located near the continent of Africa, and Sri Lanka is located near the continent of Asia.

Answer: The Andaman and Nicobar Islands in the Bay of Bengal are examples of the peaks of submerged mountains.