Ocean

The ocean is the vast body of salt water that covers most of Earth's surface. It is divided into five major parts, including the Pacific Ocean, Atlantic Ocean, Indian Ocean, Antarctic/Southern Ocean, and Arctic Ocean. These oceans are home to many plants, animals, and tiny organisms, many of which produce the oxygen we breathe.

Oceans help shape our planet's climate and weather. They store and move energy around the world through currents like the Gulf Stream and Kuroshio Current. These currents help control temperatures and affect rain and wind patterns.

Life in the ocean ranges from the sunlit surface, where plants and tiny algae make food, to the deep, dark waters far below. This rich environment supports many different species, which we often eat. However, oceans face threats from pollution, overfishing, and changes in climate, which can harm the plants and animals that live there.

Terminology

The terms "the ocean" and "the sea" mean all the salt water that covers most of Earth. This includes the Pacific, Atlantic, Indian, Antarctic/Southern, and Arctic oceans. Sometimes "sea" refers to smaller parts of the ocean that are partly surrounded by land, like the North Sea or the Red Sea.

The idea of the "World Ocean" started in the early 1900s by a Russian scientist named Yuly Shokalsky. He used it to talk about the one big ocean that connects and wraps around most of Earth. This helps scientists who study the ocean, called oceanography. The word "ocean" comes from an old story about a giant river that the ancient Greeks and Romans believed encircled the world.

Natural history

Further information: List of ancient oceans

Origin of water

Further information: Origin of water on Earth

Scientists think Earth may have had water from the start, even as it was forming. Over time, gases from volcanic activity and space impacts added more water vapor to the air. As Earth cooled, this water vapor became liquid and formed the first oceans. These early oceans might have been hot and green because of iron.

We know water was on Earth as early as 3.8 billion years ago from special rocks found in Quebec, Canada. Some studies suggest Earth may have always had enough water to fill its oceans.

Ocean formation

Main article: Paleoceanography

How Earth's oceans formed is still a mystery, but they likely appeared very early. The movement of Earth's plates, changes in ice, and rising sea levels have reshaped coastlines and oceans over time. In cold periods, lots of water was stored as ice, making oceans lower. In warm periods, oceans were higher.

Geography

Further information: Water distribution on Earth

The ocean covers most of Earth. About 70.8% of Earth's surface is water. It holds 97% of all Earth's water. Because of this, Earth is often called a "water world" or an "ocean world". The ocean is divided into parts, including the Pacific, Atlantic, Indian, Arctic, and Southern (Antarctic) oceans. These divisions help us learn about the big water around us.

The ocean's farthest point from land is called "Point Nemo", in the South Pacific Ocean. This spot is far from any land and is sometimes called the "spacecraft cemetery" because old spacecraft often fall there. The ocean also has smaller parts like seas, gulfs, and straits. These are important for travel and marine life.

Physical properties

Ocean water is the largest body of water on Earth. It makes up about 97% of all the water on our planet. The ocean helps shape our climate and weather. It covers most of Earth and helps control things like rainfall and temperature.

The ocean's surface is where we see waves and tides. Waves are made when wind blows over the water. They can be big or small, depending on the wind. Tides are the regular rising and falling of ocean water. They are mainly caused by the pull of the Moon and the Sun on Earth's water. These movements change water levels near coasts.

Deep below the surface, the ocean has many layers. Each layer has different temperatures and light. These layers help support many sea creatures and plants.

Chemical properties

Main article: Seawater § Properties

The ocean's water has many dissolved salts. This is called salinity. Salinity changes in different parts of the ocean. It is usually about 34.7 parts in a thousand. Salinity affects how cold water can get before it freezes and how hot it can get before it boils.

Ocean water also holds gases like oxygen, carbon dioxide, and nitrogen. These gases dissolve better in cold water. Tiny plants in the ocean, called phytoplankton, use carbon dioxide and make oxygen. But when these plants die, they sink and use up oxygen. This can create areas where sea creatures cannot live.

Marine life

Main articles: Marine life, Marine habitats, Marine primary production, Marine biology, and Marine ecosystem

The ocean is home to many amazing plants and animals. They have lived there for billions of years, long before any life appeared on land. The kinds of plants and animals you find depend on how deep you go and how far you are from the shore.

Many animals live in the ocean. Some of these animals include sponges, corals, jellyfish, lobsters, crabs, shrimp, fish, sharks, whales, dolphins, octopuses, and squids. Some birds, like seagulls, penguins, and pelicans, also live near the ocean. Sea turtles spend their time in the water too. Plants in the ocean include sea grasses and mangroves. Algae come in many shapes and sizes, from tiny single-celled types to larger seaweed like kelp. Bacteria and other tiny organisms called archaea are found all throughout the ocean.

Human uses of the oceans

Main articles: Sea § Humans and the sea, and The sea in culture

The ocean has been important to humans for a long time. People use the ocean to travel, for trade, and to move goods between seaports around the world. Many foods come from the ocean through fishing and aquaculture.

The ocean also gives us energy from ocean waves, tides, and wind turbines in the water. It contains valuable resources like petroleum and natural gas that we get using special equipment.

Threats from human activities

Further information: Human impact on marine life

Human activities can harm marine life and marine habitats. This happens in several ways. One way is pollution, like plastic waste in the water. Another way is overfishing, which means taking too many fish from the ocean. Climate change also causes problems, such as ocean acidification.

These activities can upset the balance of ocean ecosystems. They affect many plants and animals that live in the sea. It is important for everyone to help protect our oceans and the life they support.

Protection

Main articles: Marine conservation and marine protected area

Ocean protection helps keep ocean ecosystems safe for humans and nature. One way to protect oceans is by creating special areas called marine protected areas. In these areas, human activities are limited to keep the ocean healthy.

We can also protect oceans by making rules to stop pollution, helping important habitats like coral reefs, and supporting sustainable fishing and aquaculture. There are projects that work to clean up the ocean, such as removing plastic waste.

In 2023, an important agreement called the High Seas Treaty was signed. This treaty helps countries create protected areas in international waters. It aims to protect 30% of the world's oceans by 2030 to keep them healthy for both nature and people.