01
New crust forms at a ridge
Hot rock rises where two ocean plates move apart. It cools and becomes new seafloor.
Earth & space · 25 minutes
The seafloor is a moving tape
Magma rises at a ridge, cools into rock, and moves away on both sides. Earth's magnetic field sometimes reverses direction.
Keep this question in mindWhat evidence shows that Earth's surface moves?
01
Notice the problem
Rock records motion that no person can see.
Magnetic stripes match across the ridge and grow older with distance.
A barcode under the oceanRock records motion that no person can see.
Magnetic stripes match across the ridge and grow older with distance.
02
Three things to notice
Look at these three ideas.
Each picture shows one part of the question. You will test the ideas next.
02
Cooling rock records a direction
Magnetic minerals line up with Earth's field while the rock is hot, then lock in place as it cools.
03
Old crust moves away
Each new strip pushes earlier seafloor farther from the ridge on both sides.
03
Your prediction
If the seafloor spreads from the ridge, where should magnetic stripes appear?
Choose what you think will happen. It is fine to be wrong. The experiment will help you find out.
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