What would you find if you dug a hole straight down?
What makes topsoil dark and crumbly?
What is subsoil, the lighter layer below the topsoil?
What is bedrock?
What is the deepest hole people have ever drilled?
Why does it get hotter the deeper you go underground?
What is the water table?
Why does mud get so sticky and slippery?
What is the frost line, and why are pipes buried below it?
What is a pingo, a hill with an ice heart?
How can solid-looking ground hold both air and water?
Why is soil different colors in different places?
Why does frozen ground push rocks up to the surface?
Why does water sink through sand but sit on top of clay?
Where does rainwater go when it soaks into the ground?
Why does the ground sometimes sink to make a sinkhole?
Why is there always leftover dirt when you fill a hole back in?
Why can you see stripes in a road cut or riverbank?
How long does it take to make an inch of topsoil?
What happens to things we bury in the ground?
How can a jar of muddy water show the layers in soil?
How deep does life go underground?
How does an excavator dig so powerfully?
How does a tunnel boring machine work?
What holds up the roof while a tunnel is being dug?
How do workers get fresh air in a long tunnel?
How do builders dig a tunnel from both ends and meet in the middle?
How long can a tunnel be?
How do builders make tunnels under rivers and seas?
How did people dig tunnels before machines?
What is a mine?
What useful things come out of mines?
How do miners reach a deep ore deposit?
How do mines stay safe for workers?
Why is there a giant salt mine under Lake Huron?
Why do open-pit mines look like giant steps?
Why are mining trucks so huge?
How do we get metal out of rock?
Why is Sudbury, Ontario, famous for mining?
How deep is the deepest mine in the world?
How do miners break up hard rock?
