Theory Of Continental Drift

• Alfred Wegener

• It is this German man to

whom we credit with the

proposal of the theory of

Continental Drift.

• https://youtu.be/_5q8hz

F9VVE?t=181

• While pondering the similarities between the coastlines of South America and Africa, Wegener came up with an idea:

• What if the continents were once all connected and just drifted over the years?

Continental Drift

• The continents drift at a

rate of 2 inches a year.

• This process started 200

million years ago

• What evidence do we

have?

– Fossil and rock/mountain

correlation

– Paleoclimate data

Canadian Correction

• J. Tuzo Wilson

• the 1960’s Canadian scientist who resurrected Wegener’s theory after years of disbelief by the science community.

• Today, we know that that's false, thanks to the discovery of crustal plates.

• The plates of the earth are not composed of just land; they're composed of ocean too.

Plates of the earth p. 12

Plate Tectonics

• Within Earth is energy – heat & pressure acting upon

crust – called Tectonic Activity

• Tectonic plates move or float on top of the upper mantle.

• However they do not float freely. The plates are forced in

specific directions by the flow of magma beneath.

• This movement produces landscape features like

mountains!

Plate Tectonics – cont’d

• The magma closer to the core heats and then risestowards the surface as its density decreases.

• Once the rising magma reaches the lithosphere it moves in opposite directions.

• The magma forms convectional currents.

Plate Tectonics – Convection Currents

Divergent Boundaries

• Tensional Forces occur where two tectonic plates

are pushed apart. The tension is created as the

plates move away from each other.

• Ridge Zones sometimes occur where two plates

move apart. The magma rises between the plates

and forms a ridge.

• Again caused by convectional currents in the

magma

Tensional Forces – Ridge Zones

This diagram above shows “Sea Floor Spreading”

Oceanic ridge

Where’s the TENSION?

Convergent Boundaries

• Compressional Forces occur where two tectonic

plates come together. They compress against each

other.

• Subduction Zones sometimes occur where

compressional forces result from two plates colliding

and one plate slips under the other.

• Again caused by convectional currents in the

magma

Compressional Forces – Subduction

Mountain Formation

Where’s the Subduction /

Compression?

More about Plate Tectonics

• our text p. 10 - 12