Ocean

The ocean is the vast body of salt water that covers about 71% 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 countless plants, animals, and tiny organisms, many of which produce the oxygen we breathe.

Oceans play a crucial role in shaping our planet's climate and weather. They act like a giant heat reservoir, storing and moving energy around the world through currents like the Gulf Stream and Kuroshio Current. These currents help regulate temperatures and influence patterns of rain and wind.

Life in the ocean varies from the sunlit surface, where plants and microscopic algae use sunlight to create food, to the deep, dark waters far below. This rich environment supports a huge variety of species, many of which we rely on for food. However, oceans also face serious threats from pollution, overfishing, and changes in climate, which can harm the plants and animals that call them home.

Terminology

The terms "the ocean" and "the sea" usually 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" was introduced in the early 1900s by a Russian scientist named Yuly Shokalsky. He used it to describe 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 believe that Earth may have had water from the very beginning, even as it was forming. Over time, gases from volcanic activity and impacts from space added more water vapor to the air. As Earth cooled, this water vapor turned into liquid and formed the first oceans. These early oceans might have been very hot and looked green because of iron in the water.

We know that water was present on Earth as early as 3.8 billion years ago because of special rocks found in Quebec, Canada. Some studies even suggest that Earth may have always had enough water to fill its oceans since it formed.

Ocean formation

Main article: Paleoceanography

The exact way Earth's oceans formed is still a mystery, but they likely appeared very early in Earth's history. The movement of Earth's plates, changes in ice levels, and rising sea levels have constantly reshaped coastlines and the shape of the oceans over time. During cold periods, large amounts of water were stored in ice, making oceans lower. In warm periods, oceans were higher.

Geography

Further information: Water distribution on Earth

The ocean covers most of Earth, with about 70.8% of the planet's surface being 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 different parts, including the Pacific, Atlantic, Indian, Arctic, and Southern (Antarctic) oceans. These divisions help us understand and study the vast water body that surrounds us.

The ocean reaches its furthest point from land at a spot called "Point Nemo", located in the South Pacific Ocean. This place is far from any nearby land and is sometimes called the "spacecraft cemetery" because old spacecraft often fall here. The ocean also has many smaller parts like seas, gulfs, and straits, which are all important for navigation and marine life.

Physical properties

Ocean water is the largest body of water in the world, making up about 97% of all Earth's water. It plays a big role in shaping our planet's climate and weather. The ocean covers most of Earth and helps control things like rainfall and temperature around the world.

The ocean's surface is where we often see waves and tides. Waves are created when wind blows over the water, and they can vary in size depending on how strong and long the wind blows. Tides are the regular rising and falling of ocean water, mainly caused by the pull of the Moon and the Sun on Earth's water. These movements affect coastal areas and can create big changes in water level. Deep below the surface, the ocean has many layers, each with different temperatures and amounts of light. These layers help support a wide variety of sea creatures and plants.

Chemical properties

Main article: Seawater § Properties

The ocean's water contains many dissolved salts, which affect its properties. Salinity, a measure of these salts, changes with where you are in the ocean. It is usually around 34.7 parts per thousand. Salinity impacts 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 colder water. Plants in the ocean, called phytoplankton, use carbon dioxide and release oxygen. However, when these plants die, they sink and use up oxygen, which can create areas with very little oxygen where many sea creatures cannot survive.

Marine life

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

The ocean is full of amazing life that has lived there for billions of years, long before any life appeared on land. The types of plants and animals you can find depend a lot on how deep you go and how far you are from the shore.

Many kinds of animals live in the ocean, including sponges, corals, jellyfish, lobsters, crabs, shrimp, fish, sharks, whales, dolphins, octopuses, and squids. Even some birds like seagulls, penguins, and pelicans, as well as sea turtles, have made the ocean their home. Plants in the ocean include sea grasses and mangroves, while algae come in many forms, from tiny single-celled types to larger seaweed like kelp. Bacteria and other tiny organisms called archaea are also 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 for travel, trade, and moving goods between seaports around the world. Many things we use, like food, come from the ocean through fishing and aquaculture.

The ocean also provides energy through ocean waves, tides, and wind turbines placed in the water. It even holds valuable resources like petroleum and natural gas that we extract using special equipment.

Threats from human activities

Further information: Human impact on marine life

Human activities can harm marine life and marine habitats in several ways. These include marine pollution, such as plastic waste in the water, overfishing which takes too many fish from the ocean, and problems caused by climate change like ocean acidification.

These activities disrupt the balance of ocean ecosystems and affect many plants and animals that live in the sea. It's 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 the ecosystems in the oceans safe so humans can continue to rely on them. One important way to protect oceans is by creating and managing special areas called marine protected areas where human activities are limited. Other ways to protect oceans include making rules to stop pollution, helping important habitats like coral reefs, and supporting sustainable fishing and aquaculture. There are also projects aimed at cleaning up the ocean, like removing plastic waste.

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