Continental Drift and the Theory of Plate Tectonics

Who created the first modern atlas?

Abraham Ortelius

Which meteorologist proposed the theory of continental drift?

Alfred Wegener

In what year was the theory of continental drift proposed?

1912

What evidence is there to support the theory of continental drift?

• the theory of plate tectonics

• Mesosaurus fossils

• geological columns

• plant fossils

• animal fossils

• complimentary continent shapes

plate tectonics

the process whereby heated rock is moved within the Earth in vast convection currents, which drag along the underside of the Earth’s plates, forcing them to slowly drift across the planet

What is the thickness of conintental crust?

30-70km

What is the age of continental crust?

over 1,500 million years old

What is the density of continental crust?

2.6g/cm³

What is the composition of continental crust?

mainly granite

What is the thickness of oceanic crust?

6-10km

What is the age of oceanic crust?

less than 200 million years old

What is the density of oceanic crust?

3.0g/cm³

What is the composition of oceanic crust?

mainly basalt

What was discovered by Dietz?

• an alternating North/South magnetic striping pattern

• each rock stripe is 400,000 years old

• the oldest rocks are the furthest away from the Mid-Atlantic Ridge

• the ocean crust is slowly spreading away from the boundary

• sea floor spreading

How did Harry Hess support Dietz’s theory of sea floor spreading?

• explained that the convection currents were the driving force behind sea floor spreading

• found evidence of sea floor spreading, confirmed by palaeomagnetism

palaeomagnetism

the swapping of magnetic north and south poles every 400,000 years or so

convection currents

1. Heat from the core (hot spots) warms the mantle, causing it to rise up

2. This movement within the mantle moves the plates above it

3. The mantle nearer the surface cools and creates new crust

4. The mantle moves back down towards the core

ridge push

1. At a constructive plate boundary, plates are pulling apart

2. Magma rises to the surface and forms new crust

3. This heats the surrounding rocks, which expand and rise above the surface, creating a slope

4. New crust cools and becomes denser, sliding downslope away from the late margin

5. This puts pressure on the plates, causing them to pull apart

slab pull

1. At destructive plate margins, denser crust is forced under less dense crust

2. The sinking of the plate edge pulls the rest of the plate towards the boundary