"Natural Science 4" is an interactive encyclopedia that includes scientific information in the understanding of fourth grade students, wonderfully illustrated and animated.
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* Chapter 2 Lesson 9 *
* The Sea *
You already know that more than three quarters of the planet's surface is covered by seas and oceans. Because of this fact, seen from the cosmos, the Earth is blue.
Seas and oceans are bodies of still, deep, salty water. But did you know that the marine aquatic environment is considered the cradle of life? More than 4 billion years ago, the first life forms appeared in the water of the oceans. They were not visible to the naked eye.
The water temperature of the seas and oceans differs depending on their geographical location, as well as their depth. Depending on these factors, different living things are encountered.
Today, the seas and oceans are home to a multitude of plants and animals, from plankton to whales.
Plankton consists of living organisms, algae and animals (larvae, crustaceans, worms, jellyfish). These creatures are so small that they can only be seen under a microscope. A bucket of seawater contains millions of such organisms. Although it is so small, plankton is the basis of the food of marine animals. Corals, mussels, oysters and jellyfish feed on plankton in shallow water. Some fish, such as mackerel, eat it early in life. The largest marine animal, the blue fin whale, filters tons of plankton and krill.
The main consumers of plankton are fish and squid. Schools of small fish abound in surface marine waters and in turn attract larger predators. The Portuguese frigate (blue jellyfish) floats on the surface, where it spreads its poisonous tentacles up to 9 meters long to catch small fish.
Seabirds, such as the wandering albatross and cormorant, soar above the waves in search of fish. Some catch fish from the surface with their beaks or claws, others dive into the water to catch their prey.
In the deep, small fish are caught by larger and faster predators such as tuna or sharks, as well as turtles, seals, dolphins and whales. To survive in the face of so many predators, many fish defend themselves with protective coloring, spines or bony plates.
In tropical areas, in the clear waters near the shores, at shallow depths where the sun's rays penetrate, coral reefs live. They are home to a variety of life forms: jellyfish, clams, snails, octopuses, crabs, starfish and more.
Do creatures live in the dark depths of the seas? If so, how did they do it?