Tectonics Lesson 2: Plate Tectonic Theory

Question 1

James Hutton theory

Answer 1

1785
Process of erosion, deposition and uplift were connected and operated continuously - driven by Earth’s internal heat.
Earth older than 6000 years
‘Theory of the Earth’

Question 2

Alfred Wegener theory

Answer 2

1912
Continental drift
200 million years ago a supercontinent called Pangaea broke into pieces forming fragments today

Question 3

Harry Hess theory

Answer 3

1962
Proposed that ridges on the ocean floor were the result of molten rock rising from the asthenosphere
Hypothesis of seafloor spreading
Discovered oceans are shallower in the middle and identified mid-ocean ridges as high as 1.5 km above the sea floor

Question 4

John Tuzo Wilson

Answer 4

1963
Volcanic island chains are created by fixed ‘hotspots’
1965
Transform faults (conservative plate boundaries)

Question 5

How many fragments is the lithosphere broken up into?

Answer 5

7 major and several minor

Question 6

How do plates move?

Answer 6

Relative to each other over the asthenosphere through a number of process

Question 7

Define asthenosphere

Answer 7

Part of the mantle below the lithosphere where the rock is semi-molten

Question 8

Describe mantle convection

Answer 8

Heat produced by the decay of radioactive elements in the Earth’s core heats the lower mantle creating convection currents
These currents move spherically in the asthenosphere - moves the plates

Question 9

Describe slab pull

Answer 9

Newly formed oceanic crust at mid-ocean ridges becomes deeper and thicker as it cools
This causes it to sink into the mantle under its own weight pulling the rest of the plate down as well

Question 10

Describe subduction

Answer 10

Process of plate destruction
2 oceanic or an oceanic and continental plate move towards each other, one slides underneath the other into the mantle, melting into an area called the subduction zone

Question 11

Describe seafloor spreading

Answer 11

New crust pushes plates apart
Mid-ocean ridges and underwater mountain ranges in the middle of oceans
Formed from hot magma forced up from the asthenosphere forming new oceanic crust

Question 12

Describe palaeomagnetism

Answer 12

1950s studies confirmed seafloor was spreading.
Every 400,000 years the Earth’s magnetic field changes direction
Lava cools to rock, minerals in the rock lines up with the Earth’s magnetic direction at the time

Question 13

How much do plates move up to each year?

Answer 13

15cm