Mystery of the Ocean


We call Earth Our Blue Planet because more than 70% of its surface is covered with water: oceans, seas, rivers, lakes and huge areas of ice.

The largest blue areas are the world’s oceans.

  • They make up 97% of our planet’s water.
  • They are always on the move (waves, tides and currents).
  • On the ocean floor there are plains, mountains, volcanoes and volcanic eruptions like those on land.
  • The deepest parts of the ocean landscape are trenches: long, narrow, deep, dark and mysterious; the deepest one is the Mariana Trench in the Pacific Ocean (10,994m deep) – you can compare it to Mount Everest, which is 8,848m high.
  • Perhaps the most mysterious detail about the oceans is the fact that 95% of the underwater world remains unexplored. Will man ever find out what creatures live deep down?
  • Over 1 million known species of plants and animals (50% of all known species on Earth) live in the oceans; they come in all kinds of weird shapes, colours and sizes.
  • Marine biologists are scientists who study marine life (organisms which live in seas and oceans).

Two particularly interesting kinds of marine animals:


  • mammals: breathe air into lungs; warm-blooded; feed their young milk; have (very little) hair;
  • live in all of the world’s oceans (different species);
  • diet: depending on the species, it can range from microscopic plankton to large marine mammals;
  • many whales migrate long distances each year; they travel alone or in groups (pods);
  • active in water: jump high out of water and back; thrust their tails out of water and slap the surface; communicate with each other using very loud sounds that can be heard for many miles; sleep (like all mammals) but not for too long (they have to break the surface in order to breathe).


  • fish: breathe through gills (5 to 7 on each side of the body); have skeletons more flexible and lighter than bone; have multiple rows of teeth (lose them on a regular basis, new teeth grow and replace those); their ‘skin’ is made up of scales (outer skeleton for easy movement and for saving energy);
  • have lived in the Earth’s oceans for 450 million years (they existed long before dinosaurs appeared);
  • diet: at (or near) the top of the food chain; they are very important for the oceans’ ecosystems;
  • over 465 known species: live at various temperatures, in deep or shallow waters, on the ocean floor or in the open ocean, swim in salty or fresh waters;
  • most sharks are active in the evening or at night.

Coral reefs

  • diverse ecosystems, housing tens of thousands of marine species;
  • corals – ancient animals; an individual coral = a polyp (a very small and simple organism); they are animals that act like plants (they stay in one place and get some of their energy from the sun);
  • thousands of identical polyps live together and form a coral colony; each polyp ‘produces’ calcium carbonate exoskeleton beneath itself and over long periods of time the skeletons of many coral colonies build the structure of a coral reef;
  • many other species (fish, invertebrates, algae and microorganisms) make their homes on and around a coral reef;
  • live in shallow (≠deep) waters because of sunlight: various types of algae live inside corals, provide them with food and help them to grow;
  • found all around the world in tropical and subtropical oceans.

Polar seas

  • the Arctic Ocean and the Southern Ocean;
  • low temperatures, sea ice;
  • marine biodiversity reaches a minimum in the polar oceans: diving birds (penguins, puffins), marine mammals (whales, seals, walruses, polar bears), invertebrates and microscopic creatures.

Explore the ocean live with Dr Robert Ballard and his international team of explorers:

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