WORLD GEOGRAPHY 3202

INTRODUCTIONThe Size of the World

The Earth’s Interior

• Crust (Lithosphere)• Mantle• Outer Core• Inner Core

Inner Core• The deepest part of the

earth (1512 miles deep) is a solid that contains both iron and nickel.

• It is because of this that the center of the earth is a magnet, a compass.

• It generates a magnetic field that protects the earth from flying out of orbit.

Outer Core• Outside of the inner core

lays the outer core (1419 miles deep).

• This is much like the inner core with the exception that it is a liquid that contains sulphur and oxygen (which lowers the melting point).

Mantle• Occupying 1789 miles of

the earth is the magma (iron and magnesium) that makes up the mantle.

• Upper and lower• It is extremely hot!!• goopy; very plastic-like.

(upper mantle)• Mostly solid (lower

mantle)

Crust• Also called lithosphere• This is the top layer of the

earth, which is basically hardened mantle (magma).

• It contains two segments, the oceanic and continental crusts.

• Note: this is the same crust, it just depends how thick it is to determine if it is part of the Oceanic or Continental Crust.

Read About Earth’s interior

• Our Text p. 4-6

Theory Of Continental Drift• Alfred Wegener

• It is this German man to whom we credit with the proposal of the theory of Continental Drift.

• 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?

Wegener’s Proof

Wegener’s Proof

Wegener’s Proof

The Flaw in Wegner’s Theory

• He thought that each of the continents were a separate plate--they were just drifting on a never-changing ocean.

• Like styro-foam floating on a pool of water!!

Missing Proof

• Wegener could not explain what mechanism was powerful enough to move huge continents

• Scientist’s never believed him

Canadian Correction• J. Tuzo Wilson

• the 1960’s Canadian scientist who resurrected Wegner’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.

Canadian Correction – cont’d

• In some cases, the plates are just land, in others they're just ocean, and, in still other cases, they consist of land and ocean.

• They each have different boundaries and move in all different directions.

Plates of the earth p. 12

Continental Drift Animation

Continental Drift

• refers to the movement of the more than 20 plates (9 major) due to convergent, divergent, and transform boundaries.

• The continents drift at a rate of 2 inches a year.

• Started 200 million years ago

• Pangea (land) & Panthalasa (sea)

Plate Tectonics

• 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.

Plate Tectonics – cont’d• Plates move with the flow of magma.

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

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

• The magma forms convectional currents.

Convection 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”

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

Where’s the Subduction / Compression?