Oceans Lesson: Definition, Major Oceans, and Facts

Lesson Overview

• What Are Oceans?
• The Five Major Oceans
• How Much of Earth Do Oceans Cover?
• Oceans and the Biosphere
• Oceans and the Water Cycle
• Oceans and the Carbon Cycle
• Oceans and Earth's Water
• Who Studies Oceans?
• Ocean Animals – Who Lives Where?
• Where Did Oceans Come From?
• Earth's Systems – What's Not Covered by Oceans?

Have you ever looked at a globe and noticed how much of it is blue? That's because most of our planet is covered by oceans - vast, mysterious, and powerful bodies of saltwater that play a huge role in shaping life on Earth. Oceans are not just places for swimming or spotting sea creatures; they are essential for the planet's climate, weather, ecosystems, and even the air we breathe.

What Are Oceans?

Oceans are massive bodies of saltwater that cover most of the Earth's surface. Oceans are different from lakes or rivers because they are much larger, deeper, and made of salty water. Although we give them different names, all oceans are connected, forming one continuous global ocean.

The water in oceans is constantly moving through waves, currents, and tides. These movements help distribute heat around the planet, influence weather patterns, and support life.

The Five Major Oceans

There are five recognized oceans on Earth. Let's look at them in detail:

How Much of Earth Do Oceans Cover?

Oceans are so big that they cover about 71% of the Earth's surface. That means almost three-fourths of the Earth is water, not land.

When we look at Earth from space, we mostly see blue - that's how much water there is!

Oceans and the Biosphere

The biosphere is all the places where life exists - on land, in the air, and in water. Oceans cover about 90% of the biosphere, meaning most life on Earth lives in or depends on the oceans.

Oceans are home to:

• Tiny plankton (that produce oxygen!)
• Fish, whales, and sharks
• Coral reefs filled with thousands of species

Even land animals and people depend on oceans for food, weather, and water.

Oceans and the Water Cycle

The water cycle is how water moves through the Earth's systems. Oceans play a huge role in this cycle. Here's how:

1. Evaporation – The sun heats the ocean, turning water into vapor.
2. Condensation – The vapor rises and cools into clouds.
3. Precipitation – Clouds release water as rain or snow.
4. Collection – Water returns to oceans through rivers and streams.

Without oceans, we wouldn't have enough water in the air for rain!

Oceans and the Carbon Cycle

Another important role of oceans is in the carbon cycle. Carbon is a gas found in the air (as carbon dioxide) and in living things.

Oceans:

• Absorb carbon dioxide from the atmosphere
• Store carbon deep in the water
• Help control the Earth's climate

This process is called carbon sequestration. Without it, too much carbon dioxide would cause harmful global warming.

Oceans and Earth's Water

Most of Earth's water is stored in oceans - about 97%! But this water is salty, so we can't drink it directly. Only 3% is freshwater, found in rivers, lakes, ice, and underground.

This is why conserving freshwater is so important.

Who Studies Oceans?

People who study oceans are called oceanographers.

Oceanographers study:

• Marine animals and plants
• Ocean currents, waves, and tides
• Sea floor and underwater volcanoes
• Ocean's role in climate change

They use submarines, satellites, and research ships to learn more about the ocean's secrets.

Ocean Animals – Who Lives Where?

Many animals live in the ocean, such as:

• Octopus: Very intelligent, lives in rocky reefs.
• Shark: A predator with sharp teeth, found in all oceans.
• Starfish: Lives on the sea floor, moves using tiny feet.

But some animals do not live in oceans, like the crocodile, which prefers freshwater rivers and swamps.

Where Did Oceans Come From?

Oceans didn't appear all at once. Scientists believe they formed from outgassing, a process where water vapor came out of Earth's volcanoes billions of years ago.

Here's what happened:

1. Volcanoes erupted and released gases, including water vapor.
2. The vapor cooled and formed clouds.
3. Rain fell for millions of years and collected in low places to form oceans.

So, oceans were not created by rocks, rainfall alone, or fish, but from Earth's early volcanic activity.

Earth's Systems – What's Not Covered by Oceans?

Earth has four main systems:

• Hydrosphere: All water - oceans, lakes, rivers (Oceans are here!)
• Biosphere: All living things (Oceans are part of this too!)
• Atmosphere: Gases around Earth (Oceans affect weather here!)
• Lithosphere: Solid part - rocks, soil, and land (Not covered by oceans)

The lithosphere is the only part not covered by ocean water.