Science & Tech

How deep is your knowledge of the ocean?

Illustrations by Liz Zonarich/Harvard Staff

Sy Boles

Harvard Staff Writer

April 21, 2026

1 min read

If you’ve got thalassophobia, this research-backed quiz is not for you.

Oceans cover about 70 percent of Earth’s surface area, but largely remain a mystery to us, particularly the deep sea. They are less mysterious to Jeffrey Marlow, author of “The Dark Frontier: Unlocking the Secrets of the Deep Sea,” who completed postdoctoral research in Harvard’s Girguis Lab and is now an assistant professor of biology at Boston University. Marlow helped us develop this quiz on the geology, chemistry, and biology of one of the strangest parts of the world.

Related story: ‘Dark Frontier’ author details life in one of Earth’s harshest environments

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1. Hydrothermal vents, hotbeds of deep-sea life, regularly reach what temperatures, measured in Fahrenheit?

120 degrees

280 degrees

410 degrees

660 degrees

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2. If you could stand at the bottom of the Challenger Deep, the deepest known point of the oceans, the pressure pushing down on your head would be about as heavy as which of the following?

A Boeing 747

Four elephants

The Empire State Building

The Moon

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3. Approximately how many microbes make their homes beneath the sediment of the sea floor?

200 billion, about twice the number of stars estimated to be in the Milky Way

6 trillion, about as many miles as there are in a light year

300 octillion — that’s 3 with 29 zeroes after it

More than a googol, or 10 to the 100th power

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4. In what way do some deep-sea microbes protect us from climate change?

They cool the surrounding sea water, lowering ocean temperatures

They eat methane, a greenhouse gas that traps heat in the atmosphere

They sequester argon, another greenhouse gas

They create porous channels in rocks, which trap methane and carbon

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5. Alvinella pompejana, also known as Pompeii worms, live in the ashy flanks of deep-sea vents and can withstand temperatures up to 200 degrees Fahrenheit. The worms are covered with microbes that produce globs of slime called deepsane. How have humans repurposed deepsane?

Ultrasound gel

Protective coating for wiring on spaceships

Data center cooling mechanisms

Anti-aging skin cream

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6. Other seafloor materials have been repurposed for human ends, from anti-cancer drugs to biodiesel processing. How big was the marine biotechnology market estimated to be in 2025?

$800 million

$1.1 billion

$6.4 billion

$32.5 billion

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7. Deep-sea-dwelling mussels in the Bathymodiolus genus in the Gulf of Mexico live hundreds of meters away from the surface world. But they’re connected to the surface in what surprising way?

They only feed around the full moon

They exhibit seasonal patterns in spawning

They’re diurnal

They enjoy jazz

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8. In 2002, a genus of worm was discovered in the corpse of a whale that had fallen to the sea floor. The worm was dubbed Osedax, a Latin description of what unusual behavior?

Eating bones

Eating eyeballs

Eating eels that feed on the whale’s meat

Swimming in the whale’s veins

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9. What is an unusual adaptation of Bathyopsurus nybelini, a deep-sea isopod first documented off the coast of Puerto Rico?

It swims upside down and backwards

It swims using flat translucent pads like ping-pong paddles

It has antennae five times the length of its body

It has no eyes

All of the above

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10. True or false: Life in deep-sea trenches tends to be more diverse near the equator and less diverse near the poles, just like on land.

True

False

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11. Which of the following bodies in the solar system is believed to contain liquid water, one of the key ingredients for life?

Venus

Charon, one of Pluto’s moons

Haumea, a dwarf planet beyond Pluto

Europa, one of Jupiter’s moons

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