The ocean covers most of our planet, yet huge parts of it have never been seen up close by people. It hides mountains taller than any on land, creatures that make their own light, and currents that act like giant rivers flowing through the sea. Every fact below is based on what ocean scientists have measured and explored, so you can share them with confidence.
When you've finished, test your knowledge of our watery world with the world geography quiz, or meet more amazing sea creatures on our animal fun facts page.
Our Big Blue Planet
- The ocean covers about 71% of Earth's surface. Seen from space, our planet looks mostly blue, which is why it's often called the Blue Planet.
- About 97% of Earth's water is in the ocean. Only a small share is fresh water, and much of that is locked away in ice and underground.
- There is really just one world ocean. The Pacific, Atlantic, Indian, Arctic and Southern Oceans are all connected, so water can flow between them.
- The Pacific is the biggest ocean. It's so large that all the land on Earth could fit inside it with room to spare.
- The average depth of the ocean is about 3,700 meters. That's deeper than many mountain peaks are tall.
- Most of the ocean has never been explored by people. Large areas of the deep sea have never been visited or seen up close, and our maps of the seafloor are far less detailed than our maps of the Moon.
- The ocean is blue because water soaks up red light. Water absorbs the red, orange and yellow parts of sunlight more than the blue, so blue light is what bounces back to our eyes.
Into the Deep
- The deepest known spot is about 11 kilometers down. It's called the Challenger Deep, at the bottom of the Mariana Trench in the Pacific Ocean.
- Mount Everest would disappear in the Mariana Trench. If you dropped the world's highest mountain into the deepest point, its peak would still be more than two kilometers underwater.
- The pressure at the bottom of the deepest trench is enormous. It's more than 1,000 times the air pressure we feel at sea level, which is why only specially built vehicles can survive a trip down there.
- Sunlight fades out quickly underwater. Below about 200 meters, there isn't enough light for plants or algae to grow, and below about 1,000 meters it is completely dark.
- Seawater can be hotter than boiling without bubbling. Hydrothermal vents on the seafloor shoot out water above 350 °C, but the crushing pressure stops it from boiling.
- Whole communities live around those vents in total darkness. Instead of relying on sunlight, the base of their food chain is bacteria that make energy from chemicals pouring out of the vents.
Ocean Animals and Plants
- The blue whale is the largest animal known to have ever lived. It's bigger than any dinosaur, and one preserved blue whale heart weighed about 180 kilograms, as much as two or three adults.
- Many deep-sea creatures can make their own light. This glow, called bioluminescence, helps them find food, attract mates, confuse predators and signal to each other.
- Ocean algae make a huge share of the oxygen we breathe. Tiny drifting plant-like life called phytoplankton produce an estimated half of the oxygen made on Earth.
- Sea stars don't have blood. Instead, they pump seawater through a network of canals to move their hundreds of tiny tube feet.
- Jellyfish have no brain, heart or bones. They are mostly water, yet they've drifted through the oceans for hundreds of millions of years.
- Sea turtles find their way back to the beaches where they hatched. Scientists believe they navigate partly by sensing Earth's magnetic field.
- Some kelp can grow more than half a meter in a single day. Giant kelp forms underwater forests that shelter fish, seals and sea otters.
- Parrotfish help make sandy beaches. They bite off chunks of coral to eat the algae on it, and grind the hard bits into fine sand that comes out the other end.
- Some parrotfish sleep in a bubble of slime. At night they wrap themselves in a mucus cocoon that seems to help protect them from tiny parasites while they rest.
- Sharks have been around longer than trees. Sharks first appeared more than 400 million years ago, while the earliest trees showed up later.
- Greenland sharks may live for centuries. A study of their eyes suggested some of these slow-moving sharks could be more than 250 years old, making them the longest-living vertebrates known.
- Octopuses can taste with their arms. Their suckers are lined with sensors that let them taste and feel whatever they touch.
- Clownfish live safely among stinging anemones. A special layer of slime on their skin protects them from the anemone's stings, and in return they help chase away fish that would nibble on the anemone.
Waves, Tides and Currents
- The Moon is the main cause of the tides. The Moon's gravity tugs on Earth's oceans, making the sea level rise and fall, usually twice a day along most coasts.
- The Bay of Fundy has some of the highest tides on Earth. In this bay between New Brunswick and Nova Scotia in Canada, the water can rise and fall by about 16 meters.
- The Gulf Stream moves more water than all the world's rivers combined. This powerful current carries warm tropical water up along the east coast of North America and across the Atlantic toward Europe.
- Wind makes most ocean waves. As wind blows across the water, it passes along energy that can travel thousands of kilometers before the waves reach a shore.
- Tsunami waves can travel as fast as a jet plane. In the deep ocean, these waves race along at hundreds of kilometers an hour, but they only grow tall as they reach shallow water.
- There's a giant waterfall under the ocean. Between Greenland and Iceland, cold, heavy water spills down a slope on the seafloor called the Denmark Strait cataract, dropping about 3.5 kilometers.
- The ocean has a slow global "conveyor belt." Cold, salty water sinks near the poles and drifts along the bottom of the sea, and scientists estimate a single drop can take around a thousand years to complete the loop.
- Rubber ducks helped scientists study currents. In 1992, thousands of bath toys fell off a cargo ship in the Pacific, and people tracking where they washed up learned more about how ocean currents flow.
Salty Science
- Most of the ocean's salt came from rocks on land. Rain slowly wears away rocks, and rivers carry tiny amounts of dissolved minerals out to sea, where they build up over time.
- If you dried up the ocean, the salt could bury the land. Spread evenly over Earth's land, the ocean's salt would make a layer more than 150 meters thick.
- Salt water freezes at a colder temperature than fresh water. Typical seawater freezes at about −2 °C instead of 0 °C.
- Sea ice is mostly fresh. When ocean water freezes, most of the salt gets pushed out of the ice and left behind in the water below.
- Salty water helps you float. Salt makes water denser, so it pushes up harder on you, which is why it's easier to float in the sea than in a swimming pool.
- There are lakes and rivers on the ocean floor. In some places, extra-salty water collects in dips on the seafloor and forms "brine pools" with their own shorelines.
Reefs, Islands and Underwater Landscapes
- The Great Barrier Reef is the largest structure built by living things. Stretching more than 2,000 kilometers along Australia's coast, it's made by countless tiny coral animals.
- Coral is an animal, not a plant. Each coral is made of tiny creatures called polyps, and many of them get food from tiny algae living inside their bodies.
- The longest mountain range on Earth is underwater. The mid-ocean ridge winds around the globe for about 65,000 kilometers, mostly hidden beneath the sea.
- Mauna Kea is taller than Everest if you measure from its base. This Hawaiian volcano starts far down on the seafloor and rises more than 10,000 meters to its peak.
- Most of Earth's volcanic eruptions happen underwater. Much of this activity takes place along the mid-ocean ridges, deep beneath the waves, where new seafloor is constantly forming.
Myths we left out
Some ocean "facts" sound great but don't hold water: - Myth: The ocean is blue because it reflects the sky. Reality: The sky can add some color, but water itself absorbs red light and looks blue even under cloudy skies. - Myth: You can see a huge floating island of plastic in the Pacific. Reality: Much of the plastic pollution there is made of small pieces spread through the water, more like a cloudy soup than a solid island. - Myth: Drinking salt water is fine in an emergency. Reality: Seawater is far too salty for the human body, and drinking it makes thirst worse. - Myth: Seashells let you hear the ocean. Reality: The "waves" you hear are background sounds from around you echoing inside the shell.
Frequently asked questions
How many oceans are there?
Geographers usually name five: the Pacific, Atlantic, Indian, Arctic and Southern Oceans. They're all connected, so scientists often talk about one global ocean.
Why is the ocean salty?
Rain wears down rocks on land, and rivers carry the dissolved minerals to the sea. When ocean water evaporates, the salt is left behind and slowly builds up.
What is the deepest part of the ocean?
The Challenger Deep, in the Mariana Trench in the western Pacific, is the deepest known spot, at roughly 11 kilometers below the surface.
Where can I find more fun facts and trivia?
Head into orbit with our space fun facts, take on a daily challenge, or browse every topic on our trivia quizzes page.