A faint planetary clue
Magnetic sense
What does Earth feel like, if you can feel it at all?
Generated interpretation
First look
Earth is a magnet. The field is faint at the surface. Some animals can still use it.
A compass answers which way. A map answers where. They are not the same gift.
Look closer
Field lines tilt. They are steep near the poles and flatter near the equator. Strength also changes from place to place.
Together, tilt and strength can mark a region of ocean the way a street sign marks a corner, only much more roughly.
Keep looking
Two families of explanation are in play: chemical reactions that care about electron spin, and tiny magnetic minerals that torque in the field.
Earth is magnetic because liquid metal in the outer core is moving. The planet is a dynamo. What animals read is only the faint surface of that engine.
In sea turtles, experiments suggest the compass and the map can be taken apart. That does not mean every animal uses two sensors. Do not draw one universal magnet in every skull.
Where else
Sea turtles, Some birds, Spiny lobsters, Some fish.
Stories that use this
A question to carry outside
If the stars go out, what is still there to read?