Raven hands out four colored crayons: brown, blue, white and green. "Today we spot systems on a family walk," she says.
"Brown for geosphere, blue for hydrosphere, white for atmosphere, green for biosphere," she explains.
Rocket is already pointing. "Puddle, blue! Tree, green! Sidewalk, brown!"
Nova laughs her chiming laugh. "Bonus points for finding two colors touching," she says. "That is an interaction."
Next week we zoom in on the hydrosphere. How much of Earth's water is fresh?