Plate Tectonics

Geologic time 0 million yr 1 second is about 1 million years

Key moment

Plate motion

Left plate

Right plate

Speed

About Plate Tectonics

A cut-open block of the Earth's outer layer, 500 km across. Two tectonic plates meet at its centre. The student sets how they move and what each is made of. A clock then counts about a million years a second, and it stops at each key moment so the event can play at its own speed.

Model details

The crust is a grid of rock parcels carried by a flow field fitted to each boundary type. The layers crumple and dive rather than sliding as rigid blocks. Uplift saturates, and the fold shapes are illustrative rather than predictive.

Vertical scale is exaggerated by roughly three to eight times. The 500 km ruler is horizontal and honest. Heights are not, because a range 6 km high on a 500 km block would be invisible.

The camera turns, tilts and zooms only a little, because a cross-section only reads as a cross-section from near one angle. Key moments move it and always return it.

The sliding boundary builds no range and no trench. Its one landform is a narrow valley along the fault, shallow on land and deep on the sea floor, and the offset in the stream and the tracks is the evidence of its motion. Divergent boundaries are left seismically quiet, which is a scope limit rather than a claim.

Sources. The sea floor deepens with the square root of its age, after Parsons and Sclater (1977). Earthquakes follow the elastic rebound model, after Reid (1910). The ocean crust is layered as the ophiolite sequence: sediment, pillow basalt, sheeted dykes and gabbro. Arc melting follows the standard picture in which water from the sinking plate lowers the melting point of the mantle above it. The volcano profile was measured from a photograph of Mayon Volcano.

How do I explore?

The block is the Earth's outer layer, cut open.
Two tectonic plates meet in the middle. Choose Push together, Pull apart or Slide past.
Choose Continent or Ocean for each plate.
Press Play at the top. The clock counts millions of years. The run stops at each key moment. Read the card, then press Continue.
Drag the block to turn it. Scroll to zoom. Double-click the block to reset the view.

What should I do/notice?

Set both plates to Continent and press Push together. The rock layers fold up into mountains.
Set the left plate to Ocean and press Push together again. The ocean plate dives under the continent.
Choose Pull apart. Hot rock rises into the gap. It cools into new crust.
Choose Slide past. No mountains or trench form. A narrow valley forms along the fault. Watch the stream and tracks where they cross the middle.
The ruler under the block is 500 km. Use it to measure the landforms.
Heights are stretched so you can see them. Widths match the ruler. Heights do not.
The brown rock under the plates is the mantle. It is solid but flows very slowly. The arrows show which way it flows.
A plate that dives into the mantle slowly becomes part of it again.

Standards

MS-ESS2-2 Construct an explanation based on evidence for how geoscience processes have changed Earth's surface at varying time and spatial scales.

The clarification asks for processes that behave gradually but are punctuated by catastrophic events. Six kinds of key moment exist across the five boundaries. Any one run raises one to three, and the timeline shows how many before they happen.

Design intent

The student sets the cause and the model supplies the effect. Relative motion and crust type together decide which boundary forms.
The mantle arrows show the flow that goes with the chosen boundary. The student still sets the motion, so the arrows follow it rather than drive it.
There is no data table. The performance expectation asks for an explanation built from a model, so the model itself is the artifact.

Discussion prompts

Two of these runs push the plates together. Why does one build a mountain range and the other a trench?
The volcano sits well back from the trench. What does that distance tell you about where the melt comes from?
Sliding past builds nothing at all. What does it produce instead, and what is your evidence?
An earthquake lasts under a minute. A mountain range takes tens of millions of years. Both sit on the same timeline. What does that tell you?