Topic 1.2: Sea floor spreading and plate tectonic theory

What are the layers of the Earth shown in the diagram?

a

b

c

d

Inner Core

Outer Core

Crust

Mantle

Convection currents cause the tectonic plates to move in different directions. Explain how convection currents cause plates to move? Use the numbers on the figure to help you explain the processes.

Firstly, the heat from the core heats up the mantle, causing it to expand and ​ ​ (a)   .

The mantle material will then spread out beneath the plates, dragging the plates along with it, causing them to move apart from each other in a ​ (b)   plate movement. ​

Over time, the hot mantle material will lose heat and ​ (c)   down, ​ (d)   the plates into the mantle.

Lastly, the mantle material will ​ (e)   up again and the whole process repeats itself.

• rise
• divergent
• convergent
• sink
• heat
• dragging

The earth's lithosphere is made up of two types of plates. The oceanic plate and the ____________ plate.

Describe one difference between the continental plate and the oceanic plate.

Answer explanation

The oceanic plate is denser than the continental plate.

The continental plate is thicker than the oceanic plate.

The oceanic plate is found beneath the oceans while continental plate is found beneath the continents / land.

What is the name of the 'force' that pulls the oceanic plate down into the mantle and causes the oceanic plate to sink beneath the continental plate?

• Slab-pull force

• Convection currents

What is sea-floor spreading?

It is a process where the two oceanic crusts are ____________ away from each other.

How will the divergence of two oceanic plates cause new oceanic crusts to be formed?

Answer explanation

When two oceanic plates diverge, a gap is formed. Magma from the mantle will rise to fill up the gap. The magma will then cool and solidify when it comes into contact with water, to form new igneous rocks/oceanic crusts, thus replacing the oceanic crusts that has been destroyed at the subduction zones.

What is the name of the landform that is formed in the sea due to the 'piling' up of the new oceanic plates that is formed at the divergent zone?

• Mid-oceanic ridge

• Volcanoes

• Oceanic trench

Why do you think the ocean temperature around the mid-oceanic ridge is warmer than the other parts of the ocean?