WORLD GEOGRAPHY 3202 INTRODUCTION The 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 lies 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!! The upper mantle is goopy and very plastic- like. The lower mantle is mostly solid.

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. (1912)

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 Wegener’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 He is the 1960’s Canadian scientist who resurrected Wegener’s theory after years of disbelief by the science community. Today, we know that Wegener’s Theory was 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?