Oceans and Sea Life

The big blue planet

If you looked at Earth from space, you would see lots of blue. That is because the ocean covers more than two thirds of our planet. The ocean is one giant body of salty water, but we give different parts of it names. There are five oceans: the Pacific (the biggest), the Atlantic, the Indian, the Southern and the Arctic.

Why is the sea salty?

Ocean water tastes salty. Rivers carry tiny bits of salt and minerals from rocks on land down to the sea. Over a very long time, that salt has built up, making the ocean salty. The freshwater you drink at home does not taste salty at all.

Zones of the ocean

The ocean is very deep, and it changes as you go down.

• The sunlight zone is the top layer. Sunlight reaches here, so this is where most sea plants and animals live, like fish, turtles and dolphins.
• The twilight zone is deeper and dim. Strange animals like jellyfish and squid live here.
• The deep sea is the bottom layer. It is dark, cold and the water presses down very hard. Some animals here even make their own light to find food!

Amazing sea life 🐋

The ocean is full of incredible animals:

• The blue whale is the largest animal that has ever lived — even bigger than the dinosaurs!
• Dolphins are clever and talk to each other in clicks and whistles.
• Octopuses have eight arms and can change colour to hide.
• Coral reefs look like underwater gardens. A coral is actually a tiny animal! Reefs are home to thousands of colourful fish.

The tiny giants: plankton

Floating in the sea are millions of tiny living things called plankton, far too small to see clearly. Plankton may be tiny, but they are mighty. They are food for many sea animals, and tiny plant plankton make a huge amount of the oxygen we breathe.

Protecting our oceans 💙

Sadly, plastic rubbish ends up in the sea and harms animals that mistake it for food. Oil spills and overfishing cause problems too. We can all help by using less plastic, never littering, joining a beach clean-up and recycling. A clean ocean keeps sea life safe.

Explore a shoreline

If you visit the seaside, become an ocean explorer! Look in rock pools at low tide — you might spot crabs, limpets, tiny fish and seaweed. Watch the waves roll in and out, and notice the line of seaweed and shells left on the sand. Take any litter you find home to bin it. If you cannot reach the coast, visit an aquarium to see sea creatures up close.

To learn how rain returns water to the sea, read The Water Cycle Explained. To see how plankton, fish and whales depend on each other, read Food Chains and Ecosystems.