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 scientific phenomena questions
1 · Warm-up
By total area, which place is Earth's largest desert?
- The Sahara
- The Gobi
- Antarctica
- The Arabian Desert
Show the answer, explanation, and sources
Answer: Antarctica. Antarctica is Earth's largest desert.
A desert is defined by scarce precipitation, not heat or sand. Antarctica receives very little snowfall and spans about 14.2 million square kilometers.
Sources: British Antarctic Survey and Natural History Museum, London.
2 · Warm-up
Botanically, which fruit is a true berry even though a strawberry is not?
- A peach
- An apple
- A mango
- A banana
Show the answer, explanation, and sources
Answer: A banana. A banana is botanically a berry, while a strawberry is not.
A botanical berry develops from one flower with one ovary and has fleshy layers around its seeds. Bananas qualify; strawberries are aggregate accessory fruits.
Sources: McGill University Office for Science and Society and University of California Agriculture and Natural Resources.
3 · Core
A wombat is the only known animal to routinely leave droppings in what shape?
- Cubes
- Spirals
- Hollow rings
- Flat discs
Show the answer, explanation, and sources
Answer: Cubes. Wombats routinely produce cube-shaped droppings.
Dry material and unevenly stiff regions of the intestine form the corners before exit. The flat sides may help territorial markers stay put on rocks and logs.
Sources: Georgia Institute of Technology and Cleland Wildlife Park, Government of South Australia.
4 · Core
From a vantage point high above water droplets, what complete shape can a rainbow form?
- A wider semicircle
- A complete circle
- A flattened oval
- Two concentric arcs
Show the answer, explanation, and sources
Answer: A complete circle. A rainbow can appear as a complete circle.
Sunlight refracts and reflects inside water droplets. From the ground, the horizon blocks the lower part; high above droplets, a viewer may see the rainbow close into a complete circle.
Sources: NOAA NESDIS and UK Met Office.
5 · Core
At Oklo, ore was depleted in uranium-235 and contained fission products. What process had occurred?
- A meteorite had mixed into the ore
- The deposit had partly melted
- A natural fission chain reaction had run
- Groundwater had carried uranium away
Show the answer, explanation, and sources
Answer: A natural fission chain reaction had run. A natural fission chain reaction occurred at Oklo.
About two billion years ago, uranium-rich rock at Oklo reached criticality. Groundwater slowed neutrons enough to maintain fission, leaving depleted uranium-235 and fission products behind.
Sources: International Atomic Energy Agency and U.S. Geological Survey.
6 · Core
Shark ancestors date to about 450 million years ago and the first trees to about 385 million. What is the approximate difference?
- 15 million years
- 35 million years
- 100 million years
- 65 million years
Show the answer, explanation, and sources
Answer: 65 million years. Shark ancestors predated the first trees by about 65 million years.
Shark-like scales appear around 450 million years ago, while the first trees arrived around 385 million years ago. Subtracting the dates gives a 65-million-year gap.
Sources: Natural History Museum, London and New York State Museum.
7 · Core
What movement occurs after the sun heats one side of the Eiffel Tower?
- It expands and leans away
- It contracts and leans toward
- It rotates slightly eastward
- It stays exactly the same
Show the answer, explanation, and sources
Answer: It expands and leans away. Solar heating makes the Eiffel Tower expand and lean away from the heat.
Heat expands the iron, making the tower a few millimeters taller. Uneven heating also makes its top trace a curve about 15 centimeters across during a clear day.
Sources: Société d’Exploitation de la Tour Eiffel and OpenStax.
8 · Core
Which word names the earthy scent after rain?
- Geosmin
- Petrichor
- Ozone
- Humus
Show the answer, explanation, and sources
Answer: Petrichor. The word is petrichor.
CSIRO chemists coined petrichor in 1964 from Greek petra, stone, and ichor, the gods’ ethereal blood. Moisture releases the characteristic scent from soil and rock.
Sources: Commonwealth Scientific and Industrial Research Organisation and American Chemical Society.
9 · Challenge
While a wood frog is frozen, what happens to its heartbeat?
- It speeds up and stays fast
- It slows but never stops
- It stops, then restarts on thawing
- It continues in short bursts
Show the answer, explanation, and sources
Answer: It stops, then restarts on thawing. A wood frog's heart stops during freezing and restarts during thawing.
Glucose helps protect the frog's cells while much of its body freezes. Breathing and heartbeat stop; during thawing, the heart is among the first organs to resume function.
Sources: U.S. National Park Service and Yale Peabody Museum.
10 · Challenge
At water’s triple point, which three phases coexist in equilibrium?
- Liquid, vapor, and plasma
- Ice, liquid, and plasma
- Ice, vapor, and plasma
- Ice, liquid, and vapor
Show the answer, explanation, and sources
Answer: Ice, liquid, and vapor. Ice, liquid water, and water vapor coexist at the triple point.
At about 0.01°C and 4.6 torr, solid, liquid, and gas coexist in equilibrium. Triple-point cells turn that precise condition into a temperature reference.
Sources: National Institute of Standards and Technology and Purdue University Department of Chemistry.
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