Quiz of the Day
Oceans & Seas of the World
Friday, 25 September 2026
Balboa became the first European to sight the Pacific on 25 Sep 1513 — diving into the world's oceans, seas, tides and marine geography.
1. Vasco Núñez de Balboa, the first European to sight the Pacific Ocean in 1513, was an explorer serving which crown?
- Portugal
- England
- France
- Spain
Balboa was a Spanish conquistador and explorer who led an expedition across the Isthmus of Panama in 1513. On 25 September of that year he became the first European to see the eastern shore of the Pacific from the Americas. He claimed the ocean and all its shores for the Spanish Crown.
2. Which is the largest and deepest ocean on Earth?
- Atlantic Ocean
- Arctic Ocean
- Indian Ocean
- Pacific Ocean
The Pacific Ocean covers roughly a third of Earth's surface, making it larger than all the planet's land area combined. It stretches from the Arctic in the north to the Southern Ocean in the south. It also contains the deepest known point in any ocean.
3. Balboa named the newly sighted ocean 'Mar del Sur.' What does that name mean in English?
- Calm Sea
- South Sea
- West Sea
- Great Sea
Because Balboa's party marched south across the Isthmus of Panama to reach it, he called the water 'Mar del Sur,' meaning the South Sea. The name 'Pacific' came later, coined by Ferdinand Magellan. For centuries afterward, European maps still labelled the region the South Seas.
4. Which explorer gave the Pacific Ocean its modern name, meaning 'peaceful'?
- Ferdinand Magellan
- James Cook
- Christopher Columbus
- Amerigo Vespucci
During his circumnavigation voyage around 1520, Ferdinand Magellan named the ocean 'Mar Pacífico,' meaning peaceful sea, after encountering unusually calm waters. The name stuck despite the Pacific being home to some of the world's most violent storms and typhoons. Magellan himself died in the Philippines before completing the voyage.
5. Which is the smallest and shallowest of the world's five oceans?
- Arctic Ocean
- Southern Ocean
- Atlantic Ocean
- Indian Ocean
The Arctic Ocean is the smallest and shallowest of the world's oceans, surrounding the North Pole. Much of its surface is covered by sea ice for large parts of the year. It is also the coldest ocean on the planet.
6. The rise and fall of ocean tides is caused primarily by the gravitational pull of which body?
- The Moon
- Jupiter
- Nearby ocean currents
- The Sun
Tides are driven mainly by the Moon's gravitational pull on Earth's oceans, with the Sun contributing a smaller effect. When the Sun and Moon align at new and full moons, their combined pull creates especially large 'spring' tides. When they are at right angles, weaker 'neap' tides occur.
7. Which salty body of water is so dense that swimmers float easily on its surface?
- Caspian Sea
- Red Sea
- Black Sea
- Dead Sea
The Dead Sea, bordering Jordan and Israel, is roughly ten times saltier than typical seawater. Its extreme density lets bathers float effortlessly without swimming. Its shores also sit at the lowest land elevation on Earth, hundreds of metres below sea level.
8. The Great Barrier Reef, the world's largest coral reef system, lies off the coast of which country?
- Mexico
- Philippines
- Australia
- Indonesia
The Great Barrier Reef stretches for over 2,300 kilometres off the northeast coast of Australia. It is the largest living structure on Earth and can be seen from space. The reef is home to thousands of species of fish, coral, molluscs and marine mammals.
9. Which is the second largest ocean on Earth?
- Arctic Ocean
- Southern Ocean
- Atlantic Ocean
- Indian Ocean
The Atlantic Ocean is the second largest ocean, separating the Americas from Europe and Africa. It is still slowly widening as the seafloor spreads apart at the Mid-Atlantic Ridge. This underwater mountain range is the longest such chain on the planet.
10. The deepest known point in any ocean, in the Mariana Trench, is called what?
- Galathea Depth
- Meteor Deep
- Challenger Deep
- Sirena Deep
Challenger Deep, at the southern end of the Pacific's Mariana Trench, plunges nearly 11 kilometres below the surface. It is named after HMS Challenger, whose crew first sounded these depths in the 1870s. If Mount Everest were placed inside it, its peak would still be more than a kilometre underwater.
11. The Gulf Stream, a powerful warm current that moderates Western Europe's climate, flows within which ocean?
- Pacific Ocean
- Atlantic Ocean
- Arctic Ocean
- Indian Ocean
The Gulf Stream is a warm Atlantic current that carries tropical heat from the Gulf of Mexico up along North America and toward Europe. It helps keep countries like Britain and Ireland far milder than their northern latitude would suggest. This flow is part of a larger system of ocean currents that redistribute heat around the globe.
12. In 2021 National Geographic officially recognized a fifth ocean encircling Antarctica. What is it called?
- Austral Sea
- Antarctic Ocean
- Southern Ocean
- Polar Ocean
The Southern Ocean surrounds Antarctica and is defined by the swift Antarctic Circumpolar Current rather than by surrounding continents. National Geographic began officially labelling it as the fifth ocean on World Oceans Day in 2021. Its cold, nutrient-rich waters support rich populations of krill, whales and penguins.
13. Approximately what fraction of Earth's surface is covered by oceans?
- About 81%
- About 71%
- About 51%
- About 61%
Oceans cover roughly 71 percent of Earth's surface, which is why our planet is often called the 'blue marble.' Despite this vast expanse, much of the deep ocean remains unmapped and unexplored. The oceans hold about 97 percent of all the water on Earth.
14. The Sargasso Sea is unusual because it is the only sea on Earth with no land borders. In which ocean is it found?
- South Pacific Ocean
- Southern Ocean
- Indian Ocean
- North Atlantic Ocean
The Sargasso Sea sits in the middle of the North Atlantic and is bounded not by coastlines but by four ocean currents that circle it. It is named after the floating Sargassum seaweed that drifts on its calm, deep-blue waters. This mysterious region serves as a crucial breeding ground for European and American eels.
15. Which bay on Canada's Atlantic coast experiences the highest tidal range in the world?
- Bay of Biscay
- Chesapeake Bay
- Hudson Bay
- Bay of Fundy
The Bay of Fundy, between Nova Scotia and New Brunswick, sees tides that can rise and fall by as much as 16 metres. Its funnel shape amplifies the incoming Atlantic water into these enormous swings. Around 100 billion tonnes of seawater flow in and out of the bay with each tide.