---
title: "Plate Tectonics: the Evidence and the Engine"
description: "The idea that continents move was resisted for fifty years because nobody could say what pushed them, and it was accepted when the sea floor turned out to be spreading and recording magnetic reversals"
canonical: https://lightmysky.com/learn/science/plate-tectonics-the-evidence-and-the-engine-mt_K4hJlyOZ7p
source: https://lightmysky.com/learn/science/plate-tectonics-the-evidence-and-the-engine-mt_K4hJlyOZ7p.md
retrieved: 2026-09-12
---

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# Plate Tectonics: the Evidence and the Engine

The idea that continents move was resisted for fifty years because nobody could say what pushed them, and it was accepted when the sea floor turned out to be spreading and recording magnetic reversals as it went. Density differences driving slow flow in the mantle are what make the plates move, and every boundary type follows from the direction of that motion.

Subject: Science · Area: Earth's Systems · Ages 14 to 15
Page: https://lightmysky.com/learn/science/plate-tectonics-the-evidence-and-the-engine-mt_K4hJlyOZ7p

## Ready when they can

- List the independent lines of evidence for plate motion and say what each one alone could not show
- Explain sea-floor spreading and the magnetic stripe pattern that confirmed it
- Predict the landforms, earthquakes and volcanism expected at each type of plate boundary

## Lesson: Why geologists changed their minds

About a hundred years ago Wegener said the continents had moved. Coastlines on far shores fit together, and the same fossils sat on both sides of an ocean. But no single clue could carry the case, and he could not say what pushed whole continents, so most geologists rejected his idea for fifty years.

The proof came from the sea floor. At a mid ocean ridge, fresh rock wells up and fills the gap where two plates pull apart. As each batch cools it records the direction of Earth field, like a compass frozen in stone. The stripes flip back and forth, and they mirror each other on both sides of the ridge.

**Example.** Think of a pot of soup on a stove. Hot soup rises because it is less dense, and cooler soup sinks because it is denser. The mantle creeps the same way over millions of years. That slow circling is the missing engine, and its push and pull carry the plates.

**Tip.** To read any boundary, ask which way the plates move. Pulling apart builds new sea floor. Crashing together builds mountain ranges. One plate diving under another digs deep trenches and feeds volcanoes. Sliding past each other builds earthquake faults.

**Recap.** Matching coasts and mirror stripes showed the plates move, slow mantle flow moves them, and the direction of motion decides each boundary.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Seismic Waves & Earth's Interior](https://lightmysky.com/learn/science/seismic-waves-and-earths-interior-mt__kFxuAgs6d)
- [Plate Boundaries](https://lightmysky.com/learn/science/plate-boundaries-mt_-JnOhdei6F)
- [How Tectonic Plates Move](https://lightmysky.com/learn/science/how-tectonic-plates-move-mt_gv_uoHkdjR)

## Opens up

- [Minerals and the Three Rock Families](https://lightmysky.com/learn/science/minerals-and-the-three-rock-families-mt_S0edEKh084)