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Oceans: fun facts and quiz
The essentials in 7 ideas, with fun facts, an illustrated story and a quiz to see how much you know.
The essentials
One World Ocean
Oceans cover about 71% of Earth’s surface. The five named oceans, Pacific, Atlantic, Indian, Southern and Arctic, are all connected.
Key fact
The Pacific is bigger than all the land on Earth put together.
The Deep
The deepest point, Challenger Deep in the Mariana Trench, is about 11 km down. Mount Everest would fit inside with room to spare.
Key fact
The average depth of the ocean is about 3.7 km.
Salty Seas
Seawater is salty because rivers carry dissolved minerals into the sea, and they stay behind when the water evaporates.
Key fact
About 3.5% of seawater’s weight is salt.
Tides
Tides are the daily rise and fall of the sea, caused mainly by the Moon’s gravity pulling on the oceans. Most coasts get two high tides a day.
Key fact
Canada’s Bay of Fundy has the world’s highest tides, over 15 m.
Ocean Currents
Ocean currents are rivers within the sea, driven by wind, Earth’s spin, and differences in temperature and saltiness. They carry heat around the planet.
Key fact
The Gulf Stream helps keep Western Europe mild.
Coral Reefs
Coral reefs are built by tiny animals called polyps. They cover under 1% of the ocean floor, yet shelter about a quarter of all marine species.
Key fact
The Great Barrier Reef can be seen from space.
Deep-Sea Life
Sunlight fades within about 200 metres. Below that, creatures live in darkness, and many make their own light, called bioluminescence.
Key fact
Anglerfish lure their prey with a glowing tip.
Fun facts
National Geographic only began mapping the Southern Ocean as the fifth ocean in 2021.
The deepest ocean zone, below 6,000 m, is called the hadal zone, after Hades, the Greek underworld.
The Dead Sea is so salty that people float in it without trying.
Tides are slowly braking Earth’s spin: the day grows about 2 thousandths of a second longer every century.
The cold Humboldt Current keeps the coasts of Peru and Chile cool and full of fish, despite being close to the tropics.
Coral bleaching happens when stressed corals push out the algae that give them their colour and most of their food.
Giant squid were first filmed alive in their deep-sea home in 2012.
Story: Down to the Bottom of the World
Down to the Bottom of the World
January 1960. Jacques Piccard and US Navy officer Don Walsh squeeze into a steel ball hanging under the Trieste, above the Mariana Trench.
The descent takes almost five hours. About 9 km down, a window pane cracks with a loud bang. They keep going.
They reach the bottom of Challenger Deep and stay just 20 minutes, in a cloud of silt. Nobody went back for 52 years.
True or false?
Tap your answer to see if you got it, and why.
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Question 1 of 10
Oceans cover about 70% of Earth’s surface.
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True. About 71%.
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Question 2 of 10
Mount Everest would fit inside the Mariana Trench.
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True. With over 2 km of water above its peak.
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Question 3 of 10
Rivers carry dissolved minerals into the sea.
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True. They stay behind when water evaporates.
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Question 4 of 10
The Moon’s gravity is the main cause of tides.
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True. The Sun adds a smaller pull.
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Question 5 of 10
Ocean currents carry heat from one place to another.
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True. From the tropics towards the poles.
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Question 6 of 10
Corals are animals.
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True. Tiny polyps, related to jellyfish.
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Question 7 of 10
Many deep-sea animals make their own light.
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True. To hunt, hide or signal.
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Question 8 of 10
The Atlantic is the largest ocean.
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False. The Pacific is the largest.
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Question 9 of 10
The deepest part of the ocean is about 1 km down.
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False. It’s about 11 km down.
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Question 10 of 10
Drinking seawater is a good way to stay hydrated.
Show the answer
False. It has too much salt and makes you more dehydrated.
Keep going in the app
KnowSoda learns what you know and brings back what you’re about to forget. Oceans has 6 more ideas at the Advanced and Expert levels.
Sources
- NOAA Ocean Service — Ocean facts
- Smithsonian Ocean — Deep sea and coral reefs
- Fisheries and Oceans Canada — Bay of Fundy tides
- Encyclopaedia Britannica — Mariana Trench, Gulf Stream
- NOAA — Tsunamis; hydrothermal vents; marine debris
- Lebreton et al. (2018), the Great Pacific Garbage Patch, Scientific Reports 8
- Seabed 2030 — Mapping progress
