Book 24 activities
Try it at home: 150 science activities from Book 24
Every question in A Million Whys Book 24, The Underground Expedition, ends with a "Think like a scientist" idea. Here they are in one place. Each one links to its question page, with the video and the full answer.
Expedition 1: Layers Beneath Your Feet (25)
1. What would you find if you dug a hole straight down?
With permission and a grown-up, dig a small hole in a garden. Look at the colors of the soil as you go down. Draw what you see.
Do this with a grown-up2. What makes topsoil dark and crumbly?
Compare a handful of garden soil with a handful of sand. Which is darker, clumpier, and damper?
3. What is subsoil, the lighter layer below the topsoil?
Look at a muddy bank or a freshly dug trench with a grown-up. Notice if the lower layer is a different color.
Do this with a grown-up4. What is bedrock?
Find a place where bare bedrock shows, like a rocky outcrop or cliff. Draw it and see if you can find cracks.
5. What is the deepest hole people have ever drilled?
Draw Earth as a big circle and mark a hole that is 7.6 miles deep. How small does your mark have to be?
6. Why does it get hotter the deeper you go underground?
Use a thermometer to compare the temperature of the air, the soil's surface, and the soil two inches down. Ask a grown-up to help.
Do this with a grown-up7. What is the water table?
Pour water on a tray of sand and watch it soak in. Where does the wet sand stop and the dry sand begin?
8. Why does mud get so sticky and slippery?
Mix a spoonful of clay-rich soil with a few drops of water in one cup and with lots of water in another. Compare how they feel. Wash your hands afterward.
9. What is the frost line, and why are pipes buried below it?
Look up the frost depth in your region. Mark that depth on a drawing of a house and its pipes.
10. What is a pingo, a hill with an ice heart?
Fill a small balloon or a zip bag with water, lay it under a towel, and freeze it. Notice how the frozen water bulges. How does this help you picture a pingo?
11. How can solid-looking ground hold both air and water?
Fill a cup with dry sand and add water slowly. Watch the bubbles rise as the water fills the gaps.
12. Why is soil different colors in different places?
Collect soil from three places, put each in a clear cup, and compare their colors. Which one is darkest?
13. Why does frozen ground push rocks up to the surface?
Fill a small plastic cup with water, mark the water level, and freeze it. How much did the ice rise?
14. Why does water sink through sand but sit on top of clay?
Pour the same amount of water onto a cup of sand and a cup of clay-rich soil. Time how long each takes to drain.
15. Where does rainwater go when it soaks into the ground?
Put a sponge on a tray and pour water on it slowly. Watch how much it holds and how much flows out.
16. Why does the ground sometimes sink to make a sinkhole?
With a grown-up, put a few drops of vinegar on a piece of chalk, which is a kind of limestone. Watch it fizz and wear away. Do not touch your eyes, and rinse your hands afterward.
Do this with a grown-up17. Why is there always leftover dirt when you fill a hole back in?
Fill a cup with packed soil, tip it out, and try to put it back without pressing it. What changed?
18. Why can you see stripes in a road cut or riverbank?
Layer different colors of sand or flour in a clear jar to model stripes. Which layer is at the bottom?
19. How long does it take to make an inch of topsoil?
Imagine you were alive 500 years ago. Make a timeline showing what happened while one inch of soil formed.
20. What happens to things we bury in the ground?
With a grown-up, bury a piece of apple and a piece of plastic in a pot of soil. Check them every week for a month.
Do this with a grown-up21. How can a jar of muddy water show the layers in soil?
Try the jar test with soil from your yard. Mark the layers with tape after one minute, one hour, and one day.
22. How deep does life go underground?
Imagine a creature living far underground with no sunlight. Draw it and decide what it eats.
23. What is leaf litter, and what happens to it?
Gently look through a handful of leaf litter with a magnifying glass. Count the tiny animals you find, then put them back.
24. Why does the ground smell so fresh after rain?
Next time it rains after a dry spell, go outside with a grown-up and smell the air. Describe the smell in three words.
Do this with a grown-up25. Why is soil deep in some places and thin in others?
Pour water down a pile of soil on a tray tilted at different angles. Where does the most soil wash away?
Expedition 2: Life in the Dark Ground (25)
26. How many living things can fit in a spoonful of soil?
Look at a pinch of soil on white paper with a magnifying glass. Draw any tiny creatures or bits you see.
27. What is inside an ant nest?
Draw a cross-section of an ant nest with at least four different rooms. Label what each room is for.
28. How do ants get through the winter underground?
Look for ant hills in the spring. Note when the ants first appear and what the weather is like.
29. Why do some cicadas spend 13 or 17 years underground?
If a group of cicadas came out in 2021 and they have a 17-year life cycle, in what year will they come out again?
30. What are grubs, and what do they become?
Draw the life cycle of a beetle: egg, grub, pupa, adult.
Do this with a grown-up31. How does a worm push through hard soil without legs?
Squeeze a long balloon or a sock to see how squeezing in one direction makes it longer in another.
32. How can a worm sense the world without eyes?
Gently shine a flashlight near a worm on damp soil. Watch it move away from the light, then let it be.
33. What are nematodes, and where do they live?
Draw a nematode as a very thin, clear worm. Why is it so hard to see one without a microscope?
34. How do springtails jump when they have no wings?
Draw a springtail with its spring-like tail tucked under and then released.
35. How are millipedes different from centipedes?
Look at pictures of both animals. Count the legs on one segment of each.
36. What are pill bugs, and why do they curl into balls?
Find a pill bug with a grown-up, watch it curl up, and gently put it back where you found it.
Do this with a grown-up37. Why do most animals that live in the soil see so poorly?
Sit down with a grown-up and close your eyes. Use only touch to figure out what is in a bag of small, safe objects.
Do this with a grown-up38. Do animals underground ever run out of air?
Roll paper into a tube. Hold a tissue at one end and blow gently into the other. Notice how the air moves through the tunnel.
39. How does a groundhog survive winter in its burrow?
Graph how a groundhog's weight might change over the seasons. When is it heaviest?
40. How can some frogs and toads dig themselves into the ground?
Pretend to be a spadefoot toad. Push your feet backward in a tray of sand and see how far you sink.
41. How can thousands of garter snakes share one winter den?
Find Manitoba on a map and mark the snake dens. Write one rule for watching wildlife kindly.
42. Why do so many kinds of bees nest in the ground?
Look for small holes and mounds in bare soil on a sunny spring day. Watch from a distance and draw them.
43. How do animals find food in the dark ground?
With a grown-up helper, hide a small piece of food scented with vanilla and let a friend find it blindfolded by smell. Stay sitting down or move slowly, away from stairs.
Do this with a grown-up44. What do expert diggers' bodies have in common?
Look at a garden trowel and a toy digger. Compare them with a badger's claws. What do they share?
45. Why do many animals dig to escape heat and cold?
Put a thermometer in a shady spot and another a few inches down in the soil. Compare readings at noon.
46. What is a rabbit warren, and who lives in one?
Draw a warren map with tunnels, entrances, and a nursery. Use arrows to show how rabbits move through it.
47. Why do prairie dogs build whole underground towns?
Draw a prairie dog town with mounds, tunnels, a sentry, and grass. Add labels.
48. How do small insects survive the winter in the soil?
Make a leaf pile in a corner of your yard to give insects a winter shelter. Check it in spring.
49. How can a funnel and a lamp show you what lives in soil?
Try the funnel trap with a grown-up and count the creatures you find. Release them where you found them.
Do this with a grown-up50. How do soil animals share food and recycle nutrients?
Draw a soil food web with arrows from plants to the animals that eat them.
Expedition 3: Roots & Hidden Networks (25)
51. What jobs do roots do for a plant?
Gently pull a weed with a grown-up and look at its roots. Draw what you see and label anchor, take in, and store.
Do this with a grown-up52. How do roots sense where gravity is pulling?
Sprout a bean on a damp paper towel in a clear bag. Turn it sideways and watch the root bend downward over a few days.
53. How do roots find water in the soil?
Draw a root growing toward a wet patch of soil and away from a dry patch. Add arrows to show where it bends.
54. What are root hairs, and why do roots have so many?
Sprout a radish seed on a damp paper towel and use a magnifying glass to see the fuzzy root hairs.
55. Why do roots grow around rocks instead of through them?
Place a small rock in a pot of soil with a bean seed beside it. Dig up the plant after a few weeks to see how roots grew around it.
56. What is the difference between a taproot and fibrous roots?
Draw two plants, one with a taproot and one with fibrous roots, and write which would be harder to pull up.
57. Which vegetables are really roots?
Wash and slice a carrot lengthwise with a grown-up. Look inside for the center and the thin outer layer.
Do this with a grown-up58. How far do tree roots spread?
Look at a tree and measure how wide its branches stretch. Imagine its roots spread two or three times that far.
59. Why do tree roots sometimes lift sidewalks and crack pipes?
Look for a sidewalk lifted by a tree root. Take a photo and measure how high the sidewalk has risen.
60. How do roots hold a hillside together?
Make two soil piles on trays, one with grass roots and one bare. Sprinkle water on both and compare how much soil washes away.
61. How long could the roots of one small plant stretch?
A mile is about 1,600 meters. Multiply to find about how many meters long 380 miles is. Is it more than a million?
62. What is a mycorrhiza, the partnership between roots and fungus?
Draw a root with fungus threads reaching out. Use arrows to show water going in and sugar going out.
63. What are the thin threads of a fungus that spread underground?
With a grown-up, look up photos of mycelium threads online. Draw how they branch like a tiny web.
Do this with a grown-up64. Do trees really share food through underground fungus networks?
Draw two trees connected by fungus threads and show an arrow for sharing. Add a question mark for what we still do not know.
65. How big can a single fungus grow?
Mark out the size of a football field outside using your steps. Imagine 1,800 of them side by side.
Do this with a grown-up66. Why do mushrooms sometimes grow in a circle called a fairy ring?
Look at a lawn or park after rain with a grown-up. Do you spot a circle of mushrooms? Draw it, but do not touch or eat any. Wash your hands afterward if you touched the grass.
Do this with a grown-up67. How do bean and pea roots get help from bacteria?
Look for small round lumps on the roots of a clover or pea plant. Draw what you see.
68. Is a potato a root?
Put a potato with eyes in a dark spot and see sprouts grow. Do not eat it. Observe weekly.
69. How do tulip and daffodil bulbs sleep through the cold?
Cut an onion in half with a grown-up. Look for the layers and the tiny bud in the center.
Do this with a grown-up70. Why is it so hard to dig up grass that spreads underground?
Look at a patch of grass edge with a grown-up and trace where new shoots appear in a line.
Do this with a grown-up71. How can a forest of trees be one single living thing?
Look for a stand of aspen trees near you. Do their leaves turn color at the same time?
72. Why can a cut-down tree stump grow new shoots?
Look for a cut stump or shrub with new green shoots. Draw it and mark where the new shoots grow.
Do this with a grown-up73. Why do prairie grasses have roots deeper than the plants are tall?
Draw a prairie grass with its roots to scale. Make the roots longer than the leaves above ground.
74. What is the rhizosphere, the busy zone around a root?
Draw a root with a halo around it. Label the helpers, such as bacteria and fungi, living in that zone.
75. How can scientists watch roots grow underground?
Pack a clear jar with damp paper towel and a bean seed near the glass. Measure the root every day and make a graph.
Expedition 4: Dig, Tunnel & Mine (25)
76. How does an excavator dig so powerfully?
With a grown-up, connect two needle-free syringes with a short tube filled with water. Push one and watch the other move, like an excavator’s cylinders. Do this over a tray.
Do this with a grown-up77. How does a tunnel boring machine work?
Press a round cookie cutter into soft clay to cut a tunnel shape. How is that like a TBM?
Do this with a grown-up78. What holds up the roof while a tunnel is being dug?
Build a tunnel from a cardboard tube. Cut a slit along the top and see how wrapping it with tape makes it stronger.
Do this with a grown-up79. How do workers get fresh air in a long tunnel?
Make a tunnel from a long paper tube. Use a hair-dryer on cool with a grown-up to see how fans can move air through.
Do this with a grown-up80. How do builders dig a tunnel from both ends and meet in the middle?
Have a friend start from one end of a hallway while you start from the other. Walk toward the middle with a ruler to see how close you can meet.
81. How long can a tunnel be?
Find a map of your city and stretch a string 35 miles from your home. Where does it reach?
82. How do builders make tunnels under rivers and seas?
Float a plastic bottle in a tub, then fill it with water and sink it. How is it like a tunnel section?
83. How did people dig tunnels before machines?
Draw a qanat showing the slanted tunnel underground, the vertical shafts, and the town at the end.
84. What is a mine?
Make a list of five objects in your home that came from materials dug out of the ground.
85. What useful things come out of mines?
Pick a bike or a toy. List the materials it is made from and where each might come from.
86. How do miners reach a deep ore deposit?
Draw a cross-section of a mine with a shaft, flat tunnels, and a spot marked ore.
87. How do mines stay safe for workers?
Design a safety poster for a mine with at least four rules.
88. Why is there a giant salt mine under Lake Huron?
Put some salt on an ice cube and watch it melt. Why do road crews use salt in winter?
89. Why do open-pit mines look like giant steps?
Make a pit in a tray of sand with big steps on its sides. Compare how steep sides crumble.
90. Why are mining trucks so huge?
Measure 13 feet on a wall, and mark it. Compare it with the height of your house door.
91. How do we get metal out of rock?
With a grown-up, mix sand with tiny iron filings in a sealed zip bag. Use a magnet outside the bag to pull the filings out. Do not open the bag, and wash your hands afterward.
Do this with a grown-up92. Why is Sudbury, Ontario, famous for mining?
Find Sudbury on a map of Ontario and mark it. What else is nearby?
93. How deep is the deepest mine in the world?
The CN Tower is 1,815 feet tall. How many CN Towers stack up to equal 2.5 miles (13,200 feet)?
94. How do miners break up hard rock?
Break up a chocolate bar along its grooves and observe how it splits along weak lines. Rocks also split along cracks.
95. Why do some cities build walkways underground?
Draw a map of an underground walkway connecting four buildings. Add signs that help people find their way.
96. How do builders dig a deep basement without the sides caving in?
Fill a bucket with damp sand. Scoop out a small pit with a spoon and see it cave in. Then hold the sides with cardboard and see how it stays up.
97. Why do root cellars keep food fresh?
Compare the temperature in a basement or cool room with the temperature outside. Which is steadier?
Do this with a grown-up98. Why do scientists build laboratories far underground?
Draw an underground lab with rock above it as a shield. Add arrows for cosmic rays being blocked.
99. What is the tall tower over a mine called?
Make a pulley by running a string over a pencil taped to a doorway and lifting a small bag with it.
100. How do pumps keep underground spaces dry?
Place a sponge in a pan of water and use a turkey baster to move the water into a cup, like a pump.
Expedition 5: Treasures & Deep Secrets (25)
101. What is peat, and how does it turn into coal?
Press layers of damp paper towels under a heavy book for a day. How are they like squished plant layers?
102. Why do some oil wells stand out in the ocean?
Draw an offshore platform. Label the legs, the drill, the pipes, and a helipad. Then write one safety rule for the workers who live and work on it.
103. How do geologists find oil and gas hiding deep in the rock?
Stand in a big room and clap. Listen for the echo and estimate how far away the wall is.
104. Why does oil stay trapped underground instead of floating to the top?
Put a sponge in a dish, pour on some oil and water, and notice how the oil sits above the water.
105. How do fish that live in dark caves get by without eyes?
Draw a fish that lives in a dark cave. Which senses would you give it instead of eyes? Show where they would be on its body.
106. How does the Oak Ridges Moraine soak up rain like a giant sponge?
Fill a clear cup with sand and pour in water until the lower half is wet. Use a turkey baster to pull water out of the wet sand. How is this like a well drawing water from an aquifer?
107. How does a well bring water up from underground?
Poke a straw into a cup of water, cover the top with your finger, and lift the straw. See how it holds water.
108. What is an artesian well?
Hold a clear tube full of water so one end is high, and lower the other end. See how the water flows out the low end.
109. Where does the water in a spring come from?
With a grown-up, look for a spot at a park or on a trail where water seeps out of a hillside. Draw what you see, but do not drink the water.
Do this with a grown-up110. Why do some wells run dry?
Keep a water-use log for a day. Find three ways to use less water at home.
111. Can a forked stick really find water underground?
Hold a pencil loosely between your fingers and try to keep it still with your eyes closed. Notice how it wobbles.
112. How do veins of metal form in rock?
Draw a crack in a dark rock filled with shiny stripes of mineral. Label it a vein and add arrows for the hot water that made it.
Do this with a grown-up113. Why is gold found in streams?
Mix a few bits of metal glitter into a bowl of sand. Add water and swirl gently to see what stays behind.
114. Why are there huge piles of sand and gravel in some places?
Mix pebbles, sand, and soil in a jar of water, shake, and watch how they settle in layers.
115. How can solid rock be made of tiny shells?
Look closely at a limestone building or a piece of chalk with a magnifying glass. Can you find any shapes of shells?
116. Where does the clay for bricks and pots come from?
Shape a small bowl from air-dry clay and let it harden for a day.
117. Why is there a seed vault inside a frozen mountain?
Choose three seeds from your kitchen and imagine you were keeping them safe for 100 years. What would you do?
118. What is a time capsule?
Make your own time capsule with a grown-up. Choose five items and write a letter to be opened in 10 years.
Do this with a grown-up119. Why do old things get buried deeper over time?
With a grown-up, set up a worm jar with layers of sand and soil. Watch the layers mix over a few weeks, then free the worms.
Do this with a grown-up120. What causes a landslide, and what are the warning signs?
Pile damp sand on a tray, tilt one end a little, and sprinkle water on top with a cup. Watch how the pile slumps, then push twigs in as “roots” and try again.
121. Why do basements feel cool and damp?
Place a thermometer in your basement and another outside and compare the two readings over a week.
Do this with a grown-up122. How does loose sand become solid sandstone?
Mix sand with white glue and let it dry. This is a quick model of how sandstone forms.
123. How do quarries cut big blocks of stone?
Look at the stone on a local building. Find out what kind it is and draw it.
124. What else do we make from oil besides fuel?
Look around your home for five things made from plastic. Think about what could replace them.
125. How can people use the ground's treasures wisely?
Make a plan for how your family can reduce, reuse, and recycle one thing this week.
Expedition 6: Underground Detectives & Care (25)
126. How can a machine see underground without digging?
Clap in front of a wall and listen for the echo. Does it come back sooner or later when you step farther away?
127. How can a tiny camera peek down a narrow hole?
Tape a small flashlight to a long stick and look into a tall cardboard tube. What can you see on the walls inside?
128. How do scientists take a core sample of soil?
Push a clear straw into a tub of layered sand and soil, then lift it out. What layers did you collect?
129. How do archaeologists map a dig site?
Mark a grid of squares on paper and place small objects on it. Write the square and depth of each one.
130. What happens to a fragile artifact after it comes out of the ground?
Draw a pretend artifact. Make a label card for it with where it was found, how deep, the date, and who found it.
131. Why must crews call before they dig?
Draw a street and use colored pencils to show the buried lines using the right colors.
132. What is humus, the dark crumbly part of soil?
With a grown-up, scoop a spoonful of soil from under a tree and one from a bare spot. Which is darker and crumblier? Wash your hands afterward.
Do this with a grown-up133. How can you tell what kind of soil you have just by squeezing it?
Do the squeeze test with soil from three places and write down how each feels.
134. How can scientists tell if soil is thirsty or soaked?
Weigh a cup of soil, let it dry on a tray for a few days, and weigh it again. How much water was in it?
135. How can dogs find food that grows underground?
Hide a scented object under a towel and have a friend try to find it by smell alone.
136. How do scientists count the creatures living in the ground?
Mark a square foot of ground with string, look carefully in the top layer, and count the animals you see. Put them back.
137. Can scientists listen to life in the soil?
Put your ear near the ground in a quiet park for one minute. What do you hear? Write it down.
138. How does carbon dating tell the age of buried wood or bones?
Start with 16 pennies. Take away half to show one half-life. Keep halving it until one is left.
139. What secrets can a drilled rock core hold?
Layer clay of different colors in a straw, slice it open, and read the layers like a core.
140. Why do ghostly lines show up in dry grass or crops?
Look at a park's grass in a dry spell from a high window or hill. Do you see any lines or shapes?
141. Why should you never go into an old well, mine, or tunnel?
Make a safety sign for a hidden hole. What words and pictures would warn people best?
142. Why can a deep hole in the sand cave in?
Build a sand pile and slowly add more to the top. At what angle does it start sliding?
143. Why can squished soil make it hard for plants to grow?
Press a strip of soil in a cup with your thumb and compare it with loose soil. Plant a seed in each.
144. How can people stop soil from washing or blowing away?
Spray water on two soil trays on a slope, one covered with grass and one bare. Compare the runoff.
145. How can we protect the water hidden in the ground?
Make a poster that tells people three ways to protect the water in the ground.
146. How do people heal land after a mine closes?
Pick a place near you that could use a makeover. Draw a plan for how you would transform it.
147. What goes in an underground detective kit?
Pack your own detective kit and use it on a one-square-foot patch of ground. Write down three discoveries.
148. Who works with the ground for a living?
Pick one of these jobs and write three questions you would ask a person who does it.
149. What puzzles about the ground are scientists still chasing?
Write down three questions about the ground that you would like to explore.
150. What is the big story of the world beneath our feet?
Draw a cross-section of the ground with at least five things you learned about. Share it with a friend.