Twenty questions from the sea: deep-sea creatures, record waves, currents and the parts of the ocean nobody has seen, each with the fact behind the answer. Play them as a quiz, or read the list with the answers marked.
Pick an answer and the fact behind it appears; the next question waits until you are ready. No clock, no sign-up.
Do you know this one?
Tap an answer, or press 1, 2 or 3; Enter for the next question
The same questions as the quiz, right answer highlighted and the fact under it. Print the page for a quiz night: the print layout keeps the questions and answers only. The Ocean topic in Lock&Learn holds 133 facts in all.
How many hearts does an octopus have?
Octopuses have three hearts and blue blood. Two hearts pump blood to the gills, one to the body, and copper-based blood makes it blue.
Source: NOAA
How much of the ocean have we actually seen?
More than 80% of the ocean has never been explored. We have better maps of the surface of Mars than of our own seafloor.
Source: NOAA
How big is the biggest heart on Earth?
A blue whale has the largest heart of any animal alive. It weighs around 180 kilograms and pushes blood through a body that can stretch up to 30 metres long.
Source: National Geographic
Where can you find a lake under the sea?
There are lakes and rivers at the bottom of the ocean. Super-salty brine pools collect in seafloor depressions, complete with their own shorelines, and they're toxic to most marine life.
Source: NOAA
Where does most of Earth's oxygen come from?
Most of the oxygen you breathe comes from the ocean. Scientists estimate 50-80% of Earth's oxygen is produced by oceanic plankton, not rainforests.
Source: NOAA
Could Everest fill the ocean's deepest point?
The Mariana Trench is deeper than Everest is tall. Drop Mount Everest into the Challenger Deep and its peak would still sit more than 2 km underwater.
Source: NOAA
How do sea otters stop drifting apart at night?
Sea otters wrap up in kelp so they don't drift apart. They doze in groups called rafts, often anchoring themselves in kelp. Holding paws has been seen too, mostly among otters in aquariums.
Source: Smithsonian
Which animal can age in reverse?
One jellyfish species is biologically immortal. When stressed, Turritopsis dohrnii can revert its adult cells back to a juvenile state and start life over, indefinitely.
Source: American Museum of Natural History
Which came first, sharks or trees?
Sharks are older than trees. Sharks have existed for about 450 million years; the first true trees appeared around 385 million years ago.
Source: Natural History Museum
What's the biggest thing ever built by living creatures?
The Great Barrier Reef is the largest living structure on Earth. Built by billions of tiny coral polyps, it stretches over 2,300 km and is visible from space.
Source: NOAA
Where does sound travel fastest, air or sea?
Sound travels more than four times faster underwater. Sound moves at about 1,500 metres per second in seawater versus 340 in air. Whale calls can cross entire ocean basins.
Source: NOAA
Which tiny animal throws the ocean's fastest punch?
A mantis shrimp punches with the acceleration of a bullet. Its club accelerates so fast it boils the water around it. The shockwave alone can stun prey.
Source: National Geographic
How do herring talk to each other at night?
Herring communicate by passing gas. Researchers found herring release bubbles from their rear ends in distinct patterns to keep their schools together in the dark.
Source: Biology Letters (2003)
How wide is the Pacific, really?
The Pacific Ocean is wider than five Moons in a row. At its widest, the Pacific spans about 19,000 km. You could line up five Moons across it with room to spare.
Source: NOAA
Is anything alive at the ocean's deepest point?
Life thrives even 11 km down, in total darkness. Shrimp-like amphipods and microbes live at the bottom of the Challenger Deep, nearly 11 km down. Snailfish endure the pressure too, though they stop a few km higher.
Source: NOAA
What powers whole ecosystems where no sunlight reaches?
Whole ecosystems run on chemicals instead of sunlight. Around deep-sea hydrothermal vents, bacteria turn the vent's chemicals into food through chemosynthesis, feeding entire food webs that never see the Sun.
Source: Wikipedia
How did Japan get hit by a tsunami with no local quake?
A 1700 quake in America sent an 'orphan' tsunami to Japan. Japanese records describe a tsunami in 1700 with no local quake. Scientists later traced it to a huge rupture off the Pacific Northwest, an ocean away.
Source: Wikipedia
Why is one whale known as the loneliest in the world?
One whale has sung alone in the Pacific for decades. Since the late 1980s, hydrophones have tracked a whale calling at an unusual 52 hertz, a pitch no other whale seems to answer, earning it the name 'loneliest whale'.
Source: Woods Hole Oceanographic Institution
Why is the mighty Congo River missing a delta?
The Congo River has no delta, it feeds a deep-sea canyon. Instead of piling up a delta, the Congo funnels its sediment straight into a vast submarine canyon that ferries it out to the deep ocean floor.
Source: Wikipedia
Did seagrasses always live underwater?
Seagrasses are land plants that went back to the sea. Seagrasses evolved from land plants that returned to the ocean 75 to 100 million years ago. They still flower and root in the seafloor like their ancestors did.
Source: Wikipedia
This page has 20, each with three answers and the fact that settles it. They are the first 20 of the 133 facts in the Ocean topic of Lock&Learn, which holds the rest.
Yes. Read them out, print the page (the right answers are marked) or play the quiz on a shared screen. Each question has one right answer and two plausible wrong ones, and the fact under it gives you something to say after the reveal. Please do not republish the questions elsewhere.
Every fact names its source under the answer, from space agencies and museums to encyclopedias and published research. Lock&Learn writes each one as a teaser question with three answers, and the fact that settles it.
Install Lock&Learn, then touch and hold your Lock Screen, tap Customize, tap the widget area and choose Lock&Learn. A question waits on every screen-wake; you guess, tap, and reveal the verified fact behind the answer. Pick the topics you like and the widget rotates through them.
Yes. Lock&Learn is free on iOS: every topic opens with a free preview and another question unlocks daily. Lock&Learn+ is an optional upgrade that opens every topic in full.