2. theory of plate tectonics

what are the discoveries in order

1. alfred werger

2. arthur holmes

3. WW1

4. WW2

5. hess and dietz

6. paleomagnetism

alfred wegner

• 1912

• came up with the theory of continental drift

• named supercontinent ‘pangea’ for ‘one land’

• largely rejected by anti moblists

• evidence used - geology, fossils, coal deposits in antarctica (coal needs hot and tropical conditions)

arthur holmes

• 1919

• came up with theory of plate movement explained by convection currents

WW1

• dicsovery of mid ocean ridges

• first time sonar imaging was used to create a map of the seafloor showing that there were mid ocean ridges

WW2

• seismometers were used to monitor nuclear energy

• it measured earthquakes that were occuring in belts

hess and dietz

• came up with the theory of seafloor spreading

• found oceans were shallower in the centre with younger rocks and deeper nearer continents with older rocks

• could only occur if plates were moving apart

paleomagnetism

the recoding of the earths magnetic field by magnetic particles in magma/rocks

• earths magnetic field switches approx every 400,000 years

• iron within rocks lines up with the magnetic field and then cools in place

• same pattern either side of ridges

• shows evidence of the conveyor belt movement

ridge push

the pushing force that plates experience as they slide down the asthenosphere underneath mid ocean ridges

slab pull

when gravity pulls a subducting plate into the mantle and as a result pulls the rest of the plate down