How to use this quiz: choose an answer before opening the explanation. Each answer is supported by two independent sources checked on 2026-08-27.
10 earth systems questions
1 · Warm-up
A GPS station records movement on a tectonic plate. Which familiar growth rate is comparable?
- A blade of lawn grass
- A strand of head hair
- A fingernail
- A bamboo shoot
Show the answer, explanation, and sources
Answer: A fingernail. Tectonic plates move at approximately the rate that fingernails grow.
Most plates shift only a few centimeters per year, approximately the rate of fingernail growth. Over geologic time, this movement opens oceans and raises mountains.
Sources: U.S. Geological Survey and NOAA Ocean Service.
2 · Warm-up
How hot can the air inside a lightning channel briefly become?
- Colder than a household freezer
- About as hot as boiling water
- About as hot as fresh lava
- Hotter than the Sun's surface
Show the answer, explanation, and sources
Answer: Hotter than the Sun's surface. A lightning channel can heat air above the Sun's surface temperature.
A lightning channel can heat nearby air to around 50,000°F, several times the Sun's surface temperature. That explosive heating creates thunder.
Sources: National Weather Service and NASA Disasters Program.
3 · Core
Cold, dense water descends between Greenland and Iceland. Beneath which strait is this underwater waterfall?
- Denmark Strait
- Strait of Gibraltar
- Bering Strait
- Strait of Malacca
Show the answer, explanation, and sources
Answer: Denmark Strait. The largest known waterfall lies beneath the Denmark Strait.
Cold Nordic water sinks beneath warmer Atlantic water in a drop about 3.5 kilometers tall. Its flow is much greater than that of any waterfall on land.
Sources: NOAA Ocean Service and Woods Hole Oceanographic Institution.
4 · Core
Where is most of Earth's approximately 65,000-kilometer connected mountain system located?
- Along the Andes
- Across the ocean floor
- Through the Himalayas
- Under Antarctic ice
Show the answer, explanation, and sources
Answer: Across the ocean floor. Most of the system lies along the ocean floor as the mid-ocean ridge.
The global mid-ocean ridge extends through every ocean basin as plates spread apart and magma rises. Its connected system is far longer than any mountain range on land.
Sources: NOAA Ocean Exploration and Smithsonian Ocean.
5 · Core
Lake Baikal contains roughly what share of Earth's unfrozen surface freshwater?
- About 2%
- About 10%
- About 20%
- About 50%
Show the answer, explanation, and sources
Answer: About 20%. Lake Baikal holds about one-fifth of Earth's unfrozen surface freshwater.
The ancient Siberian lake is both the world's deepest and its largest freshwater lake by volume, storing roughly 20 percent of unfrozen surface freshwater.
Sources: UNESCO World Heritage Centre and Encyclopaedia Britannica.
6 · Core
Over very long timescales, how does the Moon's tidal pull change the length of an Earth day?
- Shorter
- Random from year to year
- Exactly unchanged
- Longer
Show the answer, explanation, and sources
Answer: Longer. Tidal friction gradually lengthens Earth's day.
Ocean tides dissipate rotational energy as heat, slowing Earth's spin. The angular momentum is transferred to the Moon, which gradually moves farther away.
Sources: NASA and National Institute of Standards and Technology.
7 · Core
How can an ash plume accumulate enough electrical charge to produce lightning?
- Ash and ice particles collide and separate charge
- Hot gases ionize the plume into a steady wire
- The plume draws charge down from the ionosphere
- Magnetic minerals turn the crater into a lightning rod
Show the answer, explanation, and sources
Answer: Ash and ice particles collide and separate charge. Collisions among ash and ice particles separate electrical charge in the plume.
Colliding ash particles can exchange charge; in tall, icy plumes, ice collisions add more. Separated charges build an electric field until lightning discharges it.
Sources: U.S. Geological Survey and NOAA Institutional Repository.
8 · Core
An ROV sees a shimmering pool with its own rippling surface deep underwater. What fills it?
- Fresh meltwater trapped below saltwater
- Extra-dense, extremely salty brine
- Liquid methane leaking from rock
- Warm oil released by microbes
Show the answer, explanation, and sources
Answer: Extra-dense, extremely salty brine. Dense, highly saline brine fills these seafloor pools.
Brine can be sufficiently saltier and denser than seawater to collect in seafloor depressions. The difference in density creates a visible boundary around the pool.
Sources: NOAA Ocean Exploration and Smithsonian Ocean.
9 · Challenge
In deep water, a tsunami can travel at a speed comparable to which type of transportation?
- A sprinting person
- A highway car
- A jet airliner
- A drifting iceberg
Show the answer, explanation, and sources
Answer: A jet airliner. A deep-water tsunami can travel at jet-airliner speed.
Deep-ocean tsunami waves can travel around 800 kilometers per hour. They are low and hard to notice there, then slow and grow taller in shallow coastal water.
Sources: NOAA Ocean Service and U.S. Geological Survey.
10 · Challenge
Models indicate that Japan's 2011 earthquake shortened the day. What change increased Earth's rotation rate?
- Ocean tides briefly reversed direction
- The Moon moved into a slightly lower orbit
- The atmosphere gained extra eastward wind
- Earth's mass shifted closer to its spin axis
Show the answer, explanation, and sources
Answer: Earth's mass shifted closer to its spin axis. The earthquake may have shortened the day by about 1.8 microseconds.
The magnitude-9 earthquake shifted some of Earth's mass closer to its rotation axis. This reduced rotational inertia and slightly increased the rotation rate.
Sources: NASA Jet Propulsion Laboratory and National Geographic.
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