Our Amazing Oceans

The Blue Planet

If you could travel far out into space and look back at Earth, you would notice something straight away. Our planet is mostly blue. That blue is water — the vast, deep, rolling oceans that cover more of the Earth than all the land put together. In fact, oceans cover more than two thirds of our whole planet. This is why Earth is sometimes called the "Blue Planet."

The ocean is the largest place to live on Earth, home to more creatures than anywhere else. It is also one of the least explored. We have mapped distant planets in more detail than we have mapped the deepest parts of our own seas. In this book, we will dive in together to discover the wonders of the ocean, from the sunny waves at the surface to the dark, mysterious world far below.

One Giant Ocean

You may have heard of the Pacific, the Atlantic, the Indian, the Southern and the Arctic Oceans. We give them different names, but here is a secret: they are all joined together into one enormous ocean that wraps around the whole planet. A drop of water could travel from one ocean to another without ever leaving the sea.

Ocean water is salty. If you have ever swum in the sea and got a mouthful, you will know the taste! The salt comes from rocks and minerals that rivers have carried into the sea over millions and millions of years. The oceans are also amazingly deep. In some places, the seabed is so far down that the tallest mountain on land could sink beneath the waves and still have water far above its peak.

A Journey to the Bottom

Imagine putting on a diving suit and slowly sinking down through the ocean. As you go deeper, the ocean changes dramatically, and it is divided into layers.

Near the top is the sunlit layer. Here the water is bright and warm, lit by the Sun. Most of the sea creatures we know best live here, where there is light and plenty of food. This is where dolphins leap, turtles glide and shoals of fish flash in the sunlight.

Keep sinking, and you reach the twilight layer. The light grows dim and blue, and the water turns colder. Strange fish with big eyes live here, peering through the gloom.

Go deeper still, and you enter the midnight layer. Now it is completely dark, because no sunlight can reach this far down. It is freezing cold, and the weight of all the water above presses down with enormous pressure. You might think nothing could live here — but you would be wrong. Astonishing creatures glow with their own light, flashing and glowing in the blackness to find food and friends, just like underwater fireflies.

At the very bottom lies the deep seafloor, the least explored place on our entire planet. Scientists are still finding new and surprising creatures there every single year.

Creatures of the Sea

The ocean bursts with an incredible variety of life, from creatures too tiny to see to the largest animal that has ever lived.

The biggest is the blue whale, longer than three buses and heavier than a herd of elephants. Despite its giant size, it feeds on some of the smallest creatures in the sea — clouds of tiny floating animals called plankton. There are clever dolphins that talk to each other in clicks and whistles, eight-armed octopuses that can change colour to hide, and sharks that have patrolled the seas since long before the dinosaurs.

Tiny floating plants called plankton are some of the most important life in the ocean. They are food for countless sea creatures, and like all green plants, they make oxygen. In fact, much of the oxygen you breathe right now was made by tiny plants in the sea. The ocean truly helps every one of us to breathe.

Coral Reefs: Cities of the Sea

In warm, shallow waters, you can find one of the most colourful and crowded places in the entire ocean: a coral reef. From a distance, coral may look like rock or strange underwater plants, but it is actually made by millions of tiny living animals called coral polyps, working together over hundreds of years.

A reef is like a bustling underwater city. Bright fish of every colour dart in and out, sea turtles cruise by, and crabs, eels and starfish hide in the nooks and crannies. Coral reefs cover only a small part of the ocean, yet they are home to a huge share of all sea creatures. They are some of the busiest and most beautiful places in nature.

Waves and Tides

The surface of the ocean is always moving. Two of its most important movements are waves and tides.

Waves are mostly made by the wind. As wind blows across the sea, it pushes the water into rolling humps that travel across the surface. When these waves reach a beach, they tumble over and break, making the white foam and the splashing we love to play in.

Tides are different and even more surprising. Twice a day, the whole ocean slowly rises up the beach and then falls back again. What causes this? The answer is in the sky: the Moon. The Moon's gravity reaches all the way across space and gently pulls on the ocean, dragging the water into a bulge. As the Earth turns, this bulge moves around the planet, giving us high tide when the water comes in and low tide when it goes out. It is amazing to think that something as far away as the Moon can move the mighty oceans.

Protecting Our Oceans

The oceans give us so much. They are home to countless creatures, they make much of the oxygen we breathe, they provide food, and they help control the weather and keep our planet from getting too hot. But today, the oceans need our help.

Plastic rubbish ends up in the sea, where it can harm or trap animals that mistake it for food. Waste and chemicals can pollute the water. And as the world warms, some delicate coral reefs are becoming sick. The good news is that everyone can help, even from far inland. We can use less plastic, never drop litter, clean up beaches, and learn all we can about the sea so we know how precious it is. When we protect the oceans, we protect the whole living planet.

What We Learned

Our oceans cover most of the Earth and join together into one giant, salty sea. As you dive deeper, the water grows darker, colder and stranger, yet life thrives even in the pitch-black depths. The oceans are home to creatures great and small, from the enormous blue whale to tiny plankton that fill the air with oxygen. Waves are made by the wind, while the tides are pulled up and down by the distant Moon. The ocean is amazing, mysterious and precious — and it is ours to explore and protect.

To meet the brave people who explore the dark depths, read Explorers of the Deep Sea. Or follow the water on its endless journey around the planet in The Amazing World of Water.