Tectonic plate map
Tectonic plate theory tells us that the
Earth's outer layer is made up of a number
of pieces called plates that sit over the
mantle.
In this activity, we will investigate
evidence to find out if these plates are
stationary or if they move. Select the
highlighted location to begin.
lens Next
Tectonic plate map
Side view
Ma (million years ago)
5.00
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event

We've gone back in time 5 million years.

Here is a side view of a small area of the Pacific Ocean floor, which
is part of the Pacific plate. There
is a fairly stationary region of
rising magma (molten rock from
the mantle) under the plate.

Move the arrow in the direction it
is pointing to move the plate as
far as possible, and observe what happens.

Back Next
Tectonic plate map
Side view
Ma (million years ago)
3.90
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event
1.1 million years
Seamount

Did you notice what happened?
Hot, rising mantle creates what is called a hot spot. As you moved
the plate, the pressure at the hot spot made rising magma burst through the sea floor.

Where the magma broke through the plate, it formed an
underwater volcano called a seamount.

Now look at the year counter. In reality, it would have taken
1.1 million years for this to
happen.

Back Next
Tectonic plate map
Side view
Ma (million years ago)
3.90
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event
1.1 million years
Seamount
Check Back Next
Tectonic plate map
Side view
Ma (million years ago)
3.90
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event
1.1 million years
Seamount

Use the arrow to move the plate again and see what happens.

Back Next
Tectonic plate map
Side view
Ma (million years ago)
3.10
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event
1.1 million years
Seamount
0.8 million years
Volcanic island

The hot spot stayed in the same location, but because the plate moved over time, the pressure
from the rising magma broke through the sea floor at a new
spot.

This time more magma erupted through the plate, forming a new volcanic island.

How long did this process take?

Check Back Next
Tectonic plate map
Side view
Ma (million years ago)
3.10
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event
1.1 million years
Seamount
0.8 million years
Volcanic island
Seamount
Volcanic
island
Check Back Next
Tectonic plate map
Side view
Ma (million years ago)
3.10
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event
1.1 million years
Seamount
0.8 million years
Volcanic island

Use the arrow to move the plate again and see what happens.

Back Next
Tectonic plate map
Side view
Ma (million years ago)
1.80
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event
1.1 million years
Seamount
0.8 million years
Volcanic island
Seamount
Volcanic
island 1
Volcanic
island 2
1.3 million years
Volcanic island

It was another big eruption, which created an island.

If a geologist measured the age of the rocks in the seamount, the
first island and the second island, which would contain the oldest rocks?

Check Back Next
Tectonic plate map
Side view
Ma (million years ago)
1.80
Sea
Plate
Mantle (hot, plastic rock)
Time passed
Event
1.1 million years
Seamount
0.8 million years
Volcanic island
Seamount
Volcanic
island 1
Volcanic
island 2
1.3 million years
Volcanic island
Check Back Next
Tectonic plate map
Position A
4.7
Position B
2.5
1.6
1.1
Position C

Here is a real line of islands. The age of each island is shown in millions of years (1.1, 1.6, 2.5, 4.7).

If you were a geologist trying to find the location of the hot spot that created them, where would you look?

Check Back Next
Tectonic plate map
4.7
2.5
1.6
1.1

Select the arrow that shows the direction the plate is moving.

Arrow1 Arrow2 Arrow3 Arrow4 Back Next
Tectonic plate map
Emperor
Seamounts
North America
Pacific Ocean
Hawaiian Ridge
< 1 million years old
Hawaii

The Hawaiian Islands are part of
a long chain of islands and seamounts that stretches for
6000 kilometres across the Pacific Ocean.

Each island and seamount is a different age.

Back Next
Tectonic plate map
Emperor
Seamounts
North America
Pacific Ocean
Hawaiian Ridge
< 1 million years old
Hawaii

Presuming that the Pacific plate moves at a constant speed, if
the youngest island is less than 1 million years old and the islands halfway along the chain are 30 to 40 million years old, how old are the oldest islands in the chain?

Check Back Next
Tectonic plate map
The Hawaiian Islands

Well done! You've completed this activity. You've found out that geologists consider volcanic chains produced by hot spots as evidence that the Earth's tectonic plates are moving.

In the case of the Hawaiian Islands, the island of Hawaii is roughly above the hot spot at present. An active submarine volcano, Loihi, lies south of Hawaii. It may be the next island in the chain – it's 3 kilometres above the ocean floor, and within a kilometre of the ocean surface.

When you're ready , select another activity from the top of the screen.

Acknowledgements
X Acknowledgements

Please refer to Conditions of use.

The satellite image of the Hawaiian Islands has been reproduced by kind permission of Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC.

Back Restart
Very dense ...

More than 300 years ago, all-round smart guy Isaac Newton used his studies of gravity to calculate the average density of the Earth. He found that its overall density is twice that of the rocks near the surface.

What does this suggest?

X Acknowledgements

Please refer to Conditions of use.

Image of Sir Isaac Newton is in the public domain.

Check Acknowledgements Next
Very dense ...

Over centuries, scientists have put forward theories to describe the Earth's interior.

Given Newton's findings (and what you may already know), choose what you think is a reasonable theory.

Check Back Next
Very dense ...

How can we test the theory you chose?

We can't see the interior of the Earth. The deepest we've been able to drill down is about
12 kilometres, which is only about 0.2% of the Earth's radius.

So how can we find evidence to either support or disprove these theories?

Back Next

Perhaps the most important evidence of the Earth's interior shows up when the seismic waves caused by an earthquake are measured at different points on the Earth's surface.

There are two types of seismic waves that travel through the Earth's interior: P-waves (primary waves) and S-waves (secondary waves).

Select the P-wave and S-wave animations to see the difference.

Back Next
P-wave

Here are some properties of the seismic waves that travel through the Earth's interior:

• P-waves travel through both
   solids and liquids.
• S-waves can travel through solids
   but not through liquids.

Select Play and look at which seismic stations record S-waves and which record P-waves. Do all of them record both types?

What does this tell us about the centre of the Earth's interior?

Check Back Next

Using observations of seismic waves and other data, geologists have deduced the structure of the Earth.

The innermost layer, the inner core, is solid. It is composed almost entirely of iron.

Inner core (solid)
Back Next

Here are the other main layers.

From the seismic observations of P-waves and S-waves, we can deduce there is a liquid layer.

Select the layer you think is
liquid.

Back Next

The next layer is the mantle. It is composed of very dense rocky material that is 'plastic'. This means that the material in the mantle moves as if it is flowing very, very slowly.

Because the mantle is more like a solid than a liquid, both S-waves and P-waves can pass through it.

Back Next

The outermost layer is the crust. It is composed of solid rocks. Its thickness ranges from 5 kilometres under oceans to 70 kilometres on continents.

However, the crust is not one continuous, unbroken layer, like an eggshell. Tectonic plate theory indicates that the Earth's crust and upper mantle are broken into pieces called tectonic plates that sit over the rest of the mantle.

The word 'tectonic' comes from the Greek tekton, which means builder. Let's find out the connection.

Back Next

Here are the major tectonic plates. They fit together like a jigsaw puzzle.

See if you can find the correct location for each of the plates.

Back Next

Well done. You've assembled all the tectonic plates.

Plates consist of crust plus some upper mantle. Plate size varies greatly. They can stretch from hundreds to thousands of kilometres across.

The thickness of a plate can range from 15 kilometres in some parts to 200 kilometres in others.

Back Next

Rotate the globe to get a full view of the African tectonic plate.

You can use Show oceans to help you locate the continents.

Select the African plate.

Back Next

Now rotate the globe to get a full view of the Pacific plate – the plate that contains the Pacific Ocean. Select the plate.

Use Show oceans if you need
help.

Back Next

You've seen that the outer layer of the Earth is made up of a number of plates that 'float' on the mantle.

Play the animation to help you decide which of these statements is true.

Play Pause
Tectonic Plate
Mantle
Outer core
Check Back Next
Play Pause
Tectonic Plate
Mantle
Outer core
Check Back Next

Well done! You've finished this activity. You found out that geological evidence suggests:

The Earth has distinct layers:
the solid inner core, a molten outer core, a plastic mantle, and
a rocky crust.
The outermost layer (the crust) ranges from 5 to 70 kilometres
in depth.
The crust and upper mantle are broken into a number of plates.

When you're ready, select the next activity from the top of the screen.

Back Restart
Tectonic plate map
Tectonic plate theory tells us that the
Earth's crust and upper mantle are broken
into a number of pieces called plates that
sit over the 'plastic' part of the mantle.
The plasticity means that the material in
the mantle moves as if it is flowing very,
very slowly.
Next
Tectonic plate map
In this activity, we will investigate
evidence to find out if these plates are
stationary or if they also move.

Select the highlighted location to begin.
lens Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.89
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

We've gone back in time 5 million years.

Here is a top view and side view of a small area of the ocean floor where two plates meet under the Atlantic Ocean.

Use the arrows in the Top view to pull the plates apart as much as possible.

Compass1 Compass2 Compass3 Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.89
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

Did you notice what happened?

As the plates pulled apart, magma (molten rock from the mantle) rose up to fill the gap.

Now look at the year counter. In reality, it would have taken
110 000 years for this to happen.

Compass1 Compass2 Compass3 Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.89
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

We have a special compass that ignores the magnetic field of the Earth and measures only the magnetic fields inside rocks.

Select and move the compass to the new section of rock that has formed in the Top view.

Compass1 Compass2 Compass3 Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.89
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

The compass is indicating a magnetic field. The red part of the compass needle is pointing
north.

This happens because as magma rises to the Earth's surface, it
cools to form basalt rock. As it solidifies, a magnetic mineral in the basalt, called magnetite, lines up with the Earth's magnetic field.

The rock then carries a permanent record of the direction of the Earth’s magnetic field at the time the rock was formed.

Compass2 Compass3 Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.89
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

The magma has now solidified into basalt to fill the gap.

Use the arrows in the Top view
and try to pull the plates further apart.

Compass2 Compass3 Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.81
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

As you might expect, more magma has risen to fill the gap between the plates and has solidified to form basalt.

This has taken a further 80 000 years. A total of 190 000 years has now elapsed.

Select and move the compass to the Top view of the new section
of rock to check the magnetic
field of the new basalt.

Compass2 Compass3 Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.81
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

This time the compass needle is pointing in the opposite direction to the first compass.

What do you think explains this? Choose the option you think is the most realistic.

Compass3 Check Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.81
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

Now pull the plates further apart. Then use the compass to check
the polarity of the new section.

Compass3 Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.64
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

Notice that the magnetic polarity of the latest section of basalt is the opposite of the previous section. This is because the Earth's polarity has flipped again.

Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.64
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate
Plate boundary

If this pattern were repeated for millions of years, we would expect to see a series of magnetic stripes preserved in the rocks on either side of the boundary. The stripes on one side would mirror the stripes on the other.

What would this observation indicate?

Check Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.64
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate
Plate boundary
Check Back Next
Tectonic plate map
Side view
Ma (million years ago)
4.64
Sea
Plate
Mantle (hot, plastic rock)
Top view (without water)
Compass
Plate

Good! You've finished this activity. We investigated the South American and African plate boundary in the Atlantic Ocean.

As the plates move apart, magma rises and solidifies into basalt, which is added to the oceanic crust. Along the edge of each plate, there are new, matching strips of basalt of the same age and magnetism. As the new rocks form, the older ones move further from the boundary.

Geologists use this as evidence that, in this location, the plates are moving apart.

Now select the next activity from the top of the screen.

Back Restart

Are you sure you want to go to
a new activity?

Yes No