Oceans cover most of the Earth, yet we have mapped them less than the surface of Mars. A gentle tour of the seas — with a surprising fact after every answer.
Most of the planet is ocean, and most of the ocean is unlike anything we see from the shore: crushing pressure, total darkness, and more living things than the land holds. This quiz covers the seas and oceans, from the largest and deepest to the currents that move heat around the globe and shape the weather. The explanations connect each fact to why it matters, because the ocean is less a blank blue space than the engine room of the whole climate. It is a good way to get your bearings on the two-thirds of the world that rarely makes it into a quiz.
Every question in this quiz is listed below with its correct answer and the reasoning behind it. Play first if you would rather not see the answers — or read through as a study sheet.
Play it insteadAnswer: A. The Pacific
Why: The Pacific covers about a third of the planet's surface — larger than all the land combined.
Answer: C. The Arctic
Why: The Arctic Ocean, largely covered by sea ice, is the smallest of the five oceans.
Answer: C. The Mariana Trench
Why: The Challenger Deep in the Mariana Trench reaches about 11,000 m — deeper than Everest is tall.
Answer: B. The Dead Sea
Why: The Dead Sea is nearly ten times saltier than the ocean, making it easy to float and impossible for fish to live in.
Answer: A. The Strait of Gibraltar
Why: The Strait of Gibraltar, only about 13 km wide at its narrowest, is the gateway between the Mediterranean and the Atlantic.
Answer: D. Australia
Why: The Great Barrier Reef off Australia is the world's largest coral reef system and is visible from space.
Answer: D. The Indian
Why: The Indian Ocean is the third-largest and the warmest of the world's oceans.
Answer: B. About 71%
Why: About 71% of the planet's surface is water, the vast majority of it ocean.
Answer: A. The Sargasso Sea
Why: The Sargasso Sea in the North Atlantic is bounded by currents rather than land, and is named for its floating sargassum seaweed.
Answer: D. The Moon's gravity
Why: Tides are driven mainly by the Moon's gravity pulling on the oceans as the Earth rotates, with the Sun adding a smaller effect.
Each correct answer awards 10 XP. There is zero point penalty for incorrect guesses, encouraging learning through exploration.
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