1.2A + 1.2B

How fast do Tectonic plates move per year?

2-5cm

How thick are tectonic plates?

100km

When was Alfred Wegener’s Hypothesis made?

1912

What was Alfred Wegener’s Hypothesis made?

Now separate continents had once been joined.

What did Arthur Holmes discover in 1930?

Earth’s internal radioactive heat was the driving force of mantle convection that could move tectonic plates.

What was discovered in 1960?

The asthenosphere

What is the asthenosphere?

A weak, deformable layer beneath the lithosphere

What was discovered in the later 1960s?

There was magnetic strips in the oceanic crust of the sea bed

What are the magnetic strips?

Palaeomagnetic signals from past reversals of the Earth’s magnetic field.

What do Palaeomagnetic signals prove?

That new ocean crust is created by the process of seafloor spreading at mid ocean ridges.

Where do seafloor spreading and palaeomagnetism occur?

constructive margins

What did Wilson discover in 1965?

Transform faults

What is subduction?

One plate sinking beneath another

What focal depths do subduction zones occur at?

10-400km

__ plates subduct under __ plates.

Oceanic plates subduct under continental plates.

What is gravitational sliding?

Divergent margins have elevated altitude because of the rising heat. This creates a slop down which oceanic plates slide.

What is slab pull?

Cold, dense oceanic plate is subducted beneath less dense continental plate. The density of the oceanic plate pulls itself into the mantle

Where does slab pull occur?

Convergent boundaries