The ocean is a huge body of salty water. The ocean covers most of Earth. There is one big world ocean. It has five named parts. The Pacific is the biggest ocean.

Salt in the ocean mostly comes from rocks on land. Rain and rivers carry it to the sea.

Sunlight reaches only about the top 200 meters of the ocean. Deep down in the ocean it is dark.

The ocean floor has tall mountains. It has deep valleys called trenches. The longest mountain range on Earth is under the sea. It is called the mid-ocean ridge.

The deepest place in the ocean is called the Challenger Deep. As of November 2026, most of the deep ocean has never been seen by people.

Many deep-sea animals make their own light. An anglerfish has a glowing lure. It uses the lure to bring small fish close enough to eat.

Coral reefs are built by tiny animals called polyps.

The blue whale lives in the ocean. It is the biggest animal that has ever lived. Blue whales eat krill, which are tiny sea animals.

Much of the trash in the ocean starts on land. Microplastics are bits of plastic. They are less than five millimeters long. Sea animals and birds can mistake plastic for food.

The ocean soaks up heat from the sun. It moves the heat around the planet.

Words to know

• trenches: deep valleys
• Microplastics: tiny plastic bits
• ridge: mountain range