Slab Pull, Not Floating, Drives the Plates

Lab Brief #2

🎯 Your mission

Understand the idea. Then look for it everywhere.

⚡ The twist

The slowest changes are the biggest ones.

What you'll learn

Plates do not drift on a liquid mantle — the mantle is solid rock that creeps over millions of years. The dominant driver is slab pull: oceanic plate that has cooled and grown dense sinks at a subduction zone and drags the rest of its plate behind it, with ridge push at the spreading centre contributing a smaller share. The evidence is in the speeds: plates with long subducting margins, like the Pacific, move several times faster than plates with almost none, like the African.

Key words

slab pull
The force from a cold, dense oceanic plate sinking at a subduction zone and dragging the rest of its plate along.
subduction
The sinking of one tectonic plate beneath another where the two converge.

Make a hypothesis first

Predict: which will erode faster?

Say your guess out loud — then find out if you were right.

Step 1 of 4 · Read

Think about what you just learned: say what "slab pull" and "subduction" mean in your own words before you start.

Step 2 of 4 · Do

Use a plate motion data table to plot each major plate's speed against the length of its subducting margin. Describe the relationship you find and state what it implies about which driving force dominates.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 3

The main force driving plate motion is:

How sure are you?😐 maybe

Question 2 of 3

The mantle beneath the plates is best described as:

How sure are you?😐 maybe

Question 3 of 3

Plates with long subducting margins tend to move:

How sure are you?😐 maybe

Mind = blown

🪨 Every grain of sand on every beach used to be a mountain.

Nice work!

You got 0 of 3 right.

Next: Why Ocean Floor Is Young and Continents Are Old All lessons

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✨ More to explore

🌍 Where you see this in real life: This is shaping the ground you walk on, slowly, every single day.

🏆 Stretch challenge (try it this week): Find a rock outside and try to guess how old it is.

👨‍👩‍👧 For the dinner table: “What's the slowest change you can think of?”

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Slab Pull, Not Floating, Drives the Plates

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