Collection · COL-02

Extreme Cold

Liquid nitrogen, millikelvin fridges, a tunnel built for -40 °F, a city carved from river ice, Everest's death zone, a glacier that bleeds, a nuclear icebreaker built for 2.8 m of ice, a nebula at 1 K, snowflakes that never quite match, glacier ice that glows blue, emperor penguin dads who fast all winter, polar bears that swim between floes, Mercury's frozen nights and the tundra's permafrost.

31 case files · 62 quiz questions · Nature, Science, Tech, Locations, History, People, Dark Facts, Space

31 case files in this collection

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Free PDF: every quick fact with its ID, the write-ups, sources and a quiz with an answer key.

What Is in Extreme Cold?

31 case files where extreme cold does the work. Freeze-branding irons are copper or brass and are chilled in liquid nitrogen (-196 °C / -320 °F) or a dry ice and alcohol bath. DD-006 A superconducting quantum chip sits on the bottom plate of a dilution refrigerator at around 10–15 millikelvin, more than 180 times colder than deep space. DD-012

The Case Files, in Order

  1. 01
    DID YOU
    KNOW?    CryoBrandingDD-006

    DD-006Nature

    CryoBranding

    Farmers brand horses with freezing cold, not fire.

    Open case file →
  2. 02
    DID YOU
    KNOW?    Quantum InfrastructureDD-012

    DD-012Science+ Tech

    Quantum Infrastructure

    This golden chandelier keeps qubits colder than outer space.

    Open case file →
  3. 03
    DID YOU
    KNOW?    One Roof TownDD-008

    DD-008Locations+ History

    One Roof Town

    This Alaska town lives under one roof.

    Open case file →
  4. 04
    DID YOU
    KNOW?    Winter in HarbinDD-034

    DD-034Locations+ People

    Winter in Harbin

    Every winter, Harbin builds a city out of river ice.

    Open case file →
  5. 05
    DID YOU
    KNOW?    ForeverestDD-063

    DD-063Dark Facts+ Locations+ Nature

    Foreverest

    Why many who die on Everest are never brought down.

    Open case file →
  6. 06
    DID YOU
    KNOW?    The Glacier That BleedsDD-725

    DD-725Nature+ Locations

    The Glacier That Bleeds

    Antarctica's glacier that seems to bleed.

    Open case file →
  7. 07
    DID YOU
    KNOW?    Uranium UralDD-579

    DD-579Tech

    Uranium Ural

    Two reactors, three propellers.

    Open case file →
  8. 08
    DID YOU
    KNOW?    Cosmic FreezerDD-752

    DD-752Space

    Cosmic Freezer

    The coldest place in the universe isn't empty space.

    Open case file →
  9. 09
    DID YOU
    KNOW?    No Perfect CrystallizationsDD-288

    DD-288Nature+ Science

    No Perfect Crystallizations

    Every snowflake writes its own flight log.

    Open case file →
  10. 10
    DID YOU
    KNOW?    Iceberg BlueDD-299

    DD-299Nature+ Science

    Iceberg Blue

    Dense glacier ice glows blue.

    Open case file →
  11. 11
    DID YOU
    KNOW?    Emperor PenguinsDD-115

    DD-115Nature

    Emperor Penguins

    Emperor penguin fathers fast for about four months.

    Open case file →
  12. 12
    DID YOU
    KNOW?    PolarDD-119

    DD-119Nature

    Polar

    Polar bears are classified as marine mammals.

    Open case file →
  13. 13
    DID YOU
    KNOW?    MercuryDD-133

    DD-133Space

    Mercury

    Mercury swings by about 600 °C between day and night.

    Open case file →
  14. 14
    DID YOU
    KNOW?    Earth's Harshest BiomeDD-212

    DD-212Nature+ Science

    Earth's Harshest Biome

    Tundra soil stays frozen year-round just below the surface.

    Open case file →
  15. 15
    DID YOU
    KNOW?    The Fingers of DeathDD-264

    DD-264Nature+ Science

    The Fingers of Death

    Brinicles are tubes of ice that grow down from sea ice.

    Open case file →
  16. 16
    DID YOU
    KNOW?    What Are You Waiting For?DD-273

    DD-273Nature+ Locations

    What Are You Waiting For?

    Avalanches can reach 80 mph within seconds.

    Open case file →
  17. 17
    DID YOU
    KNOW?    Glacial WaterfallsDD-316

    DD-316Nature+ Locations

    Glacial Waterfalls

    Meltwater can pour off a glacier's edge as a waterfall.

    Open case file →
  18. 18
    DID YOU
    KNOW?    To Break the IceDD-318

    DD-318Tech+ Locations

    To Break the Ice

    Icebreakers ride up onto the ice and crush it with their weight.

    Open case file →
  19. 19
    DID YOU
    KNOW?    Preserve Your BubblesDD-326

    DD-326Science+ Nature

    Preserve Your Bubbles

    In deep cold, a soap bubble can freeze into a crystal shell.

    Open case file →
  20. 20
    DID YOU
    KNOW?    ICECOREDD-398

    DD-398Science+ Nature

    ICECORE

    Ice cores hold air bubbles hundreds of thousands of years old.

    Open case file →
  21. 21
    DID YOU
    KNOW?    nICEDD-382

    DD-382Tech

    nICE

    Ice factories freeze huge blocks, then slice them with saws.

    Open case file →
  22. 22
    DID YOU
    KNOW?    SnowplowerDD-409

    DD-409Tech

    Snowplower

    Rotary plows can throw snow far from the tracks.

    Open case file →
  23. 23
    DID YOU
    KNOW?    Advanced Bicycle Riding IIDD-419

    DD-419People

    Advanced Bicycle Riding II

    Fat bikes ride snow on extra-wide tires.

    Open case file →
  24. 24
    DID YOU
    KNOW?    FREEZINGDD-444

    DD-444Science

    FREEZING

    Ice floats because freezing water spreads out into an open lattice.

    Open case file →
  25. 25
    DID YOU
    KNOW?    Just a Chill DogDD-458

    DD-458Nature

    Just a Chill Dog

    A husky's double coat traps warm air against its skin.

    Open case file →
  26. 26
    DID YOU
    KNOW?    Immune to ColdDD-467

    DD-467Nature

    Immune to Cold

    A husky's undercoat traps warm air next to its skin.

    Open case file →
  27. 27
    DID YOU
    KNOW?    How Water FreezesDD-468

    DD-468Science

    How Water Freezes

    Freezing water locks into a six-sided lattice.

    Open case file →
  28. 28
    DID YOU
    KNOW?    Layer by LayerDD-470

    DD-470Nature

    Layer by Layer

    Ice sheets can build up in visible layers.

    Open case file →
  29. 29
    DID YOU
    KNOW?    Frozen GatorsDD-491

    DD-491Nature

    Frozen Gators

    Alligators can poke their snouts through ice to breathe.

    Open case file →
  30. 30
    DID YOU
    KNOW?    The PlungeDD-497

    DD-497Nature

    The Plunge

    Young penguins gather at the ice edge before their first swim.

    Open case file →
  31. 31
    DID YOU
    KNOW?    Feeling Froggy?DD-758

    DD-758Nature+ Science

    Feeling Froggy?

    Wood frogs can freeze solid in winter and thaw back to life.

    Open case file →

Collection Quiz

All quizzes →

62 questions from all 31 case files in Extreme Cold. Test Your Knowledge: answers are revealed instantly.

  1. Freeze-branding irons are chilled in liquid nitrogen. How cold is it?

    1. -18 °C
    2. -60 °C
    3. -196 °C
    4. -273 °C
    Show the answer

    Answer: C. -196 °C Now You Know: Liquid nitrogen is -196 °C (-320 °F). Source: DD-006 · CryoBranding · Slide 02 · Exhibit A (Liquid nitrogen: -196 °C)

  2. Why does freeze-branded hair grow back white?

    1. The cold destroys pigment cells but spares the growth follicle
    2. The iron leaves white dye in the skin
    3. The cold bleaches the hair shaft
    4. The follicle dies and is replaced by scar hair
    Show the answer

    Answer: A. The cold destroys pigment cells but spares the growth follicle Now You Know: The cold destroys the pigment cells (melanocytes) but spares the follicle, so the hair grows back colorless. Source: DD-006 · CryoBranding · Slide 03 · Exhibit B (It kills only the color)

  3. What is the gold 'chandelier' seen in photos of quantum computers?

    1. A dilution refrigerator
    2. A cooling fan array
    3. The quantum processor itself
    4. A power supply
    Show the answer

    Answer: A. A dilution refrigerator Now You Know: It's a multi-stage dilution refrigerator, and each plate down is colder. Source: DD-012 · Quantum Infrastructure · Write-up · Exhibit B (The 'chandelier' is a fridge) · An in-depth look at an IBM quantum computer (Popular Science); How Does a Dilution Refrigerator Work? (Bluefors)

  4. Where in the fridge does the quantum chip sit?

    1. At the top, at room temperature
    2. In the middle
    3. At the bottom, on the coldest plate
    4. Outside the fridge
    Show the answer

    Answer: C. At the bottom, on the coldest plate Now You Know: The processor is mounted on the mixing-chamber plate, the coldest stage, at the bottom. Source: DD-012 · Quantum Infrastructure · Write-up · Exhibit C (Chip at the bottom) · Microwave Package Design for Superconducting Quantum Processors (PRX Quantum 2, 020306, 2021); An in-depth look at an IBM quantum computer (Popular Science)

  5. How many stories tall is Begich Towers, home to most of Whittier, Alaska?

    1. 4
    2. 14
    3. 40
    4. 104
    Show the answer

    Answer: B. 14 Now You Know: Begich Towers is a 14-story tower housing most of Whittier's ~300 year-round residents. Source: DD-008 · One Roof Town · Slide 02 · Exhibit A (Begich Towers)

  6. What was Begich Towers originally built as?

    1. A luxury hotel
    2. A hospital
    3. Cold War Army barracks
    4. A prison
    Show the answer

    Answer: C. Cold War Army barracks Now You Know: The U.S. Army built it as Cold War barracks. Locals moved in after the military left. Source: DD-008 · One Roof Town · Slide 03 · Exhibit B (Built for soldiers)

  7. Which river supplies the ice for Harbin's festival?

    1. Yangtze
    2. Yellow River
    3. Songhua River
    4. Amur
    Show the answer

    Answer: C. Songhua River Now You Know: Crews cut blocks two to three feet thick from the frozen Songhua every December. Source: DD-034 · Winter in Harbin · Write-up · Exhibit C (Cut from the river) · Harbin International Ice and Snow Sculpture Festival (Wikipedia); One of the World's Largest Ice and Snow Carnivals Is Underway in China (Smithsonian Magazine)

  8. When did the modern Harbin Ice and Snow Festival begin?

    1. 1963
    2. 1985
    3. 1999
    4. 2008
    Show the answer

    Answer: B. 1985 Now You Know: It opened on January 5, 1985. The 1963 event was an ice-lantern show. Source: DD-034 · Winter in Harbin · Write-up · Exhibit B (The festival is born) · 从公园里简陋冰灯到满城冰雕雪塑 (Heilongjiang Department of Culture and Tourism, Oct. 2024); Harbin International Ice and Snow Sculpture Festival (Wikipedia); One of the World's Largest Ice and Snow Carnivals Is Underway in China (Smithsonian Magazine)

  9. About how many bodies are thought to remain on Everest?

    1. About 20
    2. More than 200
    3. More than 2,000
    4. None
    Show the answer

    Answer: B. More than 200 Now You Know: More than 300 people have died in the region over a century. Source: DD-063 · Foreverest · Write-up · Exhibit A (How many remain) · Everest: Bodies of fallen mountain climbers finally recovered from 'death zone' (BBC News, 2024); Mount Everest: Eleven tonnes of rubbish taken off Himalayan peaks (BBC News, 2024); As ice melts, Everest's 'death zone' gives up its ghosts (Phys.org / AFP, 2024)

  10. Above what altitude does the 'death zone' begin?

    1. 5,000 m
    2. 6,500 m
    3. About 8,000 m
    4. 8,849 m
    Show the answer

    Answer: C. About 8,000 m Now You Know: The air there holds about a third of sea-level oxygen. Source: DD-063 · Foreverest · Write-up · Exhibit B (The death zone) · Everest: Bodies of fallen mountain climbers finally recovered from 'death zone' (BBC News, 2024); Mount Everest (Encyclopaedia Britannica)

  11. Which glacier is Blood Falls on?

    1. Thwaites
    2. Taylor
    3. Beardmore
    4. Lambert
    Show the answer

    Answer: B. Taylor Now You Know: It's in the McMurdo Dry Valleys, ending at Lake Bonney. Source: DD-725 · The Glacier That Bleeds · Write-up · Exhibit A (Where it is) · Badgeley et al., An englacial hydrologic system of brine within a cold glacier: Blood Falls (Journal of Glaciology, 2017); Solving the mystery of Antarctica's 'Blood Falls' (Cambridge Core Blog, 2017)

  12. What was the red color first blamed on?

    1. Volcanic ash
    2. Red algae
    3. Blood from seals
    4. Paint
    Show the answer

    Answer: B. Red algae Now You Know: Griffith Taylor found the falls in 1911. Source: DD-725 · The Glacier That Bleeds · Write-up · Exhibit B (Not algae) · Researchers solve the century-old mystery of Blood Falls (University of Alaska Fairbanks); Solving the mystery of Antarctica's 'Blood Falls' (Cambridge Core Blog, 2017)

  13. How many nuclear reactors does Ural have?

    1. Two
    2. One
    3. Four
    4. Six
    Show the answer

    Answer: A. Two Now You Know: Two RITM-200 reactors. Source: DD-579 · Uranium Ural · Write-up · Exhibit C (Reactors to propellers) · Wikipedia: Ural (icebreaker); Wikipedia: Project 22220 icebreaker

  14. How many propellers does Ural have?

    1. Three
    2. One
    3. Two
    4. Four
    Show the answer

    Answer: A. Three Now You Know: Each is driven by a 20 MW electric motor. Source: DD-579 · Uranium Ural · Write-up · Exhibit C (Reactors to propellers) · Wikipedia: Ural (icebreaker); Wikipedia: Project 22220 icebreaker

  15. About how cold is the Boomerang Nebula?

    1. 1 K
    2. 2.7 K
    3. 10 K
    4. 77 K
    Show the answer

    Answer: A. 1 K Now You Know: About 1 Kelvin, or -272 °C / -458 °F, one degree above absolute zero. Source: DD-752 · Cosmic Freezer · Slide 03 · Exhibit B (1 Kelvin)

  16. What keeps empty space at about 2.7 K?

    1. Starlight from the Milky Way
    2. The Big Bang's afterglow
    3. Cosmic rays
    4. Dark matter
    Show the answer

    Answer: B. The Big Bang's afterglow Now You Know: The Big Bang's afterglow keeps space at about 2.7 K, and the Boomerang is colder than that. Source: DD-752 · Cosmic Freezer · Slide 04 · Exhibit C (Colder than space)

  17. What do snow crystals form on?

    1. A tiny particle like dust or pollen
    2. A raindrop's surface
    3. Lightning
    4. Nothing at all
    Show the answer

    Answer: A. A tiny particle like dust or pollen Now You Know: It's called nucleation. Source: DD-288 · No Perfect Crystallizations · Write-up · Exhibit A (A seed particle) · Kenneth G. Libbrecht, Caltech: SnowCrystals.com; Wikipedia: Snowflake

  18. How do snow crystals grow?

    1. Water vapor deposits onto the ice
    2. Raindrops stick together
    3. They melt and refreeze
    4. Wind sculpts them
    Show the answer

    Answer: A. Water vapor deposits onto the ice Now You Know: The vapor skips the liquid stage. Source: DD-288 · No Perfect Crystallizations · Write-up · Exhibit B (Growth from vapor) · Kenneth G. Libbrecht, Caltech: SnowCrystals.com

  19. How does glacier ice form?

    1. Snow is buried and compressed
    2. Seawater freezes
    3. Rain freezes on contact
    4. Hail piles up
    Show the answer

    Answer: A. Snow is buried and compressed Now You Know: Air bubbles are squeezed out. Source: DD-299 · Iceberg Blue · Write-up · Exhibit A (Compressed snow) · Wikipedia: Blue ice (glacial)

  20. Which light does ice absorb more?

    1. Red
    2. Blue
    3. Green only
    4. None
    Show the answer

    Answer: A. Red Now You Know: The difference is small but adds up. Source: DD-299 · Iceberg Blue · Write-up · Exhibit B (Red is absorbed) · Wikipedia: Blue ice (glacial); Wikipedia: Color of water

  21. When do emperor penguins breed?

    1. In the Antarctic winter
    2. In summer only
    3. Never on ice
    4. In spring rain
    Show the answer

    Answer: A. In the Antarctic winter Now You Know: In extreme cold. Source: DD-115 · Emperor Penguins · Write-up · Exhibit A (Winter breeders) · Wikipedia: Emperor penguin

  22. Who incubates the egg?

    1. The male
    2. The female
    3. Both in turns
    4. Neither
    Show the answer

    Answer: A. The male Now You Know: Only emperors do this. Source: DD-115 · Emperor Penguins · Write-up · Exhibit B (Egg handoff) · Wikipedia: Emperor penguin

  23. How are polar bears classified?

    1. Marine mammals
    2. Fish
    3. Reptiles
    4. Amphibians
    Show the answer

    Answer: A. Marine mammals Now You Know: They live on sea ice. Source: DD-119 · Polar · Write-up · Exhibit A (Marine mammals) · Wikipedia: Polar bear

  24. What does Ursus maritimus mean?

    1. Maritime bear
    2. Snow cat
    3. Ice wolf
    4. White giant
    Show the answer

    Answer: A. Maritime bear Now You Know: Sea bear. Source: DD-119 · Polar · Write-up · Exhibit B (Sea bear) · Wikipedia: Polar bear

  25. Why can't Mercury hold heat?

    1. It has almost no atmosphere
    2. It's too far out
    3. It has oceans
    4. It's cloudy
    Show the answer

    Answer: A. It has almost no atmosphere Now You Know: Only a thin exosphere. Source: DD-133 · Mercury · Write-up · Exhibit A (No atmosphere) · Wikipedia: Mercury (planet)

  26. How hot do days get?

    1. About 430 °C
    2. About 43 °C
    3. About 4,300 °C
    4. 0 °C
    Show the answer

    Answer: A. About 430 °C Now You Know: Hot enough to melt lead. Source: DD-133 · Mercury · Write-up · Exhibit B (430 °C days) · Wikipedia: Mercury (planet)

  27. What defines tundra?

    1. Treeless, cold land
    2. Rainforest
    3. Desert dunes
    4. Coral reef
    Show the answer

    Answer: A. Treeless, cold land Now You Know: Short growing seasons. Source: DD-212 · Earth's Harshest Biome · Write-up · Exhibit A (Treeless) · Wikipedia: Tundra

  28. Where is alpine tundra?

    1. On high mountains
    2. In oceans
    3. In caves
    4. At the equator's coast
    Show the answer

    Answer: A. On high mountains Now You Know: Also Arctic tundra. Source: DD-212 · Earth's Harshest Biome · Write-up · Exhibit B (Arctic and alpine) · Wikipedia: Tundra

  29. What is a brinicle?

    1. A hollow ice tube
    2. A fish
    3. An iceberg
    4. A volcano
    Show the answer

    Answer: A. A hollow ice tube Now You Know: Under sea ice. Source: DD-264 · The Fingers of Death · Write-up · Exhibit A (Ice tube) · Wikipedia: Brinicle

  30. What sinks to form it?

    1. Cold dense brine
    2. Fresh water
    3. Warm water
    4. Sand
    Show the answer

    Answer: A. Cold dense brine Now You Know: Expelled salt. Source: DD-264 · The Fingers of Death · Write-up · Exhibit B (Brine) · Wikipedia: Brinicle

  31. What is an avalanche?

    1. Snow sliding rapidly downhill
    2. A rockfall only
    3. A flood
    4. A storm
    Show the answer

    Answer: A. Snow sliding rapidly downhill Now You Know: A mass of snow. Source: DD-273 · What Are You Waiting For? · Write-up · Exhibit A (Definition) · Wikipedia: Avalanche

  32. What can trigger one?

    1. Heavy snowfall
    2. Sunlight only
    3. Birds
    4. Nothing
    Show the answer

    Answer: A. Heavy snowfall Now You Know: Also people. Source: DD-273 · What Are You Waiting For? · Write-up · Exhibit B (Triggers) · Wikipedia: Avalanche

  33. What feeds a glacial waterfall?

    1. Meltwater
    2. Rain only
    3. Seawater
    4. Groundwater only
    Show the answer

    Answer: A. Meltwater Now You Know: Melting ice. Source: DD-316 · Glacial Waterfalls · Write-up · Exhibit A (Meltwater) · Wikipedia: Meltwater

  34. When are they biggest?

    1. In warm seasons
    2. In midwinter
    3. At night only
    4. Never
    Show the answer

    Answer: A. In warm seasons Now You Know: More melting. Source: DD-316 · Glacial Waterfalls · Write-up · Exhibit B (Seasonal) · Wikipedia: Meltwater

  35. How do icebreakers break ice?

    1. Riding up and using their weight
    2. Lasers
    3. Explosives
    4. Heating the sea
    Show the answer

    Answer: A. Riding up and using their weight Now You Know: Sloped bows. Source: DD-318 · To Break the Ice · Write-up · Exhibit A (Purpose) · Wikipedia: Icebreaker

  36. What protects the hull?

    1. Reinforcement
    2. Paint only
    3. Rubber
    4. Nothing
    Show the answer

    Answer: A. Reinforcement Now You Know: Thick steel. Source: DD-318 · To Break the Ice · Write-up · Exhibit B (Bow) · Wikipedia: Icebreaker

  37. What is a bubble's skin?

    1. A thin soapy water film
    2. Plastic
    3. Glass
    4. Ice from the start
    Show the answer

    Answer: A. A thin soapy water film Now You Know: Very thin. Source: DD-326 · Preserve Your Bubbles · Write-up · Exhibit A (Film) · Wikipedia: Soap bubble

  38. What forms on it in the cold?

    1. Ice crystals
    2. Salt
    3. Sand
    4. Mold
    Show the answer

    Answer: A. Ice crystals Now You Know: Branching. Source: DD-326 · Preserve Your Bubbles · Write-up · Exhibit B (Freezing) · Wikipedia: Soap bubble

  39. What do bubbles preserve?

    1. Ancient air
    2. Water
    3. Fish
    4. Dust only
    Show the answer

    Answer: A. Ancient air Now You Know: Atmosphere. Source: DD-398 · ICECORE · Write-up · Exhibit A (Drilling) · Wikipedia: Ice core

  40. How far back do Antarctic cores go?

    1. About 800,000 years
    2. 100 years
    3. 10 million years
    4. 1,000 years
    Show the answer

    Answer: A. About 800,000 years Now You Know: Long record. Source: DD-398 · ICECORE · Write-up · Exhibit B (Depth) · Wikipedia: Ice core

  41. What cuts the blocks?

    1. Bandsaws
    2. Knives only
    3. Lasers only
    4. Fire
    Show the answer

    Answer: A. Bandsaws Now You Know: Industrial. Source: DD-382 · nICE · Write-up · Exhibit A (Molds) · Wikipedia: Icemaker

  42. Where is ice frozen?

    1. In molds
    2. In rivers
    3. Outdoors
    4. In bags
    Show the answer

    Answer: A. In molds Now You Know: Blocks. Source: DD-382 · nICE · Write-up · Exhibit B (Lifting) · Wikipedia: Icemaker

  43. Which plow throws snow far?

    1. Rotary
    2. Wedge
    3. Flanger
    4. Shovel
    Show the answer

    Answer: A. Rotary Now You Know: Spinning. Source: DD-409 · Snowplower · Write-up · Exhibit A (Wedge) · Wikipedia: Snowplow

  44. What does a wedge plow do?

    1. Pushes snow aside
    2. Melts it
    3. Packs it
    4. Lifts rails
    Show the answer

    Answer: A. Pushes snow aside Now You Know: Sides. Source: DD-409 · Snowplower · Write-up · Exhibit B (Rotary) · Wikipedia: Rotary snowplow

  45. What bikes are used on snow?

    1. Fat bikes
    2. Road bikes
    3. BMX only
    4. Unicycles
    Show the answer

    Answer: A. Fat bikes Now You Know: Wide tires. Source: DD-419 · Advanced Bicycle Riding II · Write-up · Exhibit A (Fat bikes) · Wikipedia: Fat bike

  46. Why low tire pressure?

    1. Flotation and grip
    2. Speed
    3. Looks
    4. Noise
    Show the answer

    Answer: A. Flotation and grip Now You Know: Snow. Source: DD-419 · Advanced Bicycle Riding II · Write-up · Exhibit B (Pressure) · Wikipedia: Fat bike

  47. What shape is the ice lattice?

    1. Hexagonal
    2. Cubic only
    3. Round
    4. Random
    Show the answer

    Answer: A. Hexagonal Now You Know: Six-sided. Source: DD-444 · FREEZING · Write-up · Exhibit A (Lattice) · Wikipedia: Ice

  48. What bonds hold it?

    1. Hydrogen bonds
    2. Ionic bonds
    3. Metal bonds
    4. Glue
    Show the answer

    Answer: A. Hydrogen bonds Now You Know: Water. Source: DD-444 · FREEZING · Write-up · Exhibit B (Bonds) · Wikipedia: Ice

  49. What coat type?

    1. Double
    2. Single
    3. None
    4. Wool
    Show the answer

    Answer: A. Double Now You Know: Two layers. Source: DD-458 · Just a Chill Dog · Write-up · Exhibit A (Coat) · Wikipedia: Siberian Husky

  50. What does the undercoat trap?

    1. Warm air
    2. Water
    3. Snow
    4. Dirt
    Show the answer

    Answer: A. Warm air Now You Know: Insulation. Source: DD-458 · Just a Chill Dog · Write-up · Exhibit B (Guard hairs) · Wikipedia: Siberian Husky

  51. Coat type?

    1. Double
    2. Single
    3. None
    4. Wool
    Show the answer

    Answer: A. Double Now You Know: Layers. Source: DD-467 · Immune to Cold · Write-up · Exhibit A (Coat) · Wikipedia: Siberian Husky

  52. Undercoat traps?

    1. Warm air
    2. Water
    3. Snow
    4. Dirt
    Show the answer

    Answer: A. Warm air Now You Know: Insulation. Source: DD-467 · Immune to Cold · Write-up · Exhibit B (Guard hairs) · Wikipedia: Siberian Husky

  53. Lattice shape?

    1. Hexagonal
    2. Square
    3. Round
    4. Random
    Show the answer

    Answer: A. Hexagonal Now You Know: Six sides. Source: DD-468 · How Water Freezes · Write-up · Exhibit A (Lattice) · Wikipedia: Ice

  54. Which bonds?

    1. Hydrogen
    2. Ionic
    3. Metallic
    4. Nuclear
    Show the answer

    Answer: A. Hydrogen Now You Know: Water. Source: DD-468 · How Water Freezes · Write-up · Exhibit B (Bonds) · Wikipedia: Ice

  55. What builds the sheets?

    1. Layers of ice
    2. Sand
    3. Snow only
    4. Salt
    Show the answer

    Answer: A. Layers of ice Now You Know: Stacking. Source: DD-470 · Layer by Layer · Write-up · Exhibit A (Formation) · Wikipedia: Ice

  56. What drives variation?

    1. Temperature swings
    2. Moonlight
    3. Fish
    4. Boats
    Show the answer

    Answer: A. Temperature swings Now You Know: Weather. Source: DD-470 · Layer by Layer · Write-up · Exhibit B (Driver) · Wikipedia: Ice

  57. Dormancy term?

    1. Brumation
    2. Hibernation only
    3. Molting
    4. Estivation
    Show the answer

    Answer: A. Brumation Now You Know: Reptiles. Source: DD-491 · Frozen Gators · Write-up · Exhibit A (State) · Wikipedia: Brumation

  58. How do they breathe?

    1. Snout above ice
    2. Gills
    3. Skin
    4. They don't
    Show the answer

    Answer: A. Snout above ice Now You Know: Nostrils. Source: DD-491 · Frozen Gators · Write-up · Exhibit B (Metabolism) · Wikipedia: Brumation

  59. Why hesitate?

    1. Predators
    2. Cold air
    3. Hunger
    4. Noise
    Show the answer

    Answer: A. Predators Now You Know: Risk. Source: DD-497 · The Plunge · Write-up · Exhibit A (Moment) · Wikipedia: Emperor penguin

  60. A predator?

    1. Leopard seal
    2. Polar bear
    3. Shark only
    4. Eagle
    Show the answer

    Answer: A. Leopard seal Now You Know: Antarctic. Source: DD-497 · The Plunge · Write-up · Exhibit B (Behavior) · Wikipedia: Emperor penguin

  61. How much body water can freeze?

    1. About 65%
    2. 5%
    3. 100%
    4. 20%
    Show the answer

    Answer: A. About 65% Now You Know: Up to 65-70%. Source: DD-758 · Feeling Froggy? · Write-up · Exhibit A (Species) · Wikipedia: Wood frog

  62. Heart while frozen?

    1. Stops
    2. Speeds up
    3. Unchanged
    4. Doubles
    Show the answer

    Answer: A. Stops Now You Know: No heartbeat. Source: DD-758 · Feeling Froggy? · Write-up · Exhibit B (Range) · Wikipedia: Wood frog