Chapter 9: Plate Tectonics Review

Feb 11, 2013

What to study?• Layers of the Earth• Convection Currents• Continental Drift• Sea-floor Spreading• Theory of Plate Tectonics• Plate Boundaries• Crustal Features• Shadow Zone• http://txstar.cpo.com/

– Username: mustang– Password: science– Study Plate Tectonics 8.9A and 8.9B

Layers of the Earth

From the Earth’s Crust to the Inner Core:Depth IncreasesPressure IncreasesTemperature Increases

Layers of the Earth Temp.

(°C)

Crust 0- 860 °C

Mantle 870°C

OuterCore

2200°C

InnerCore

5000°C

Lithosphere

• This layer is broken down into several large tectonic plates

Asthenosphere

• The asthenosphere is the semi-rigid part of the middle mantle that flows like hot asphalt under a heavy weight.

• The tectonic plates float on this semi-liquid layer.

Lithosphere Vs. Asthenosphere

Lithosphere= rigidAsthenosphere= semi-soft

Convection Currents in the Mantle

• According to scientists, convection currents is the driving force behind the movement of the Earth’s plates.

http://www.absorblearning.com/media/item.action?quick=12p#

Convection

• Heated water is less dense therefore rises while Cooled water is more dense, which sinks.

• This is also true with air

Alfred Wegener’s hypothesis on Continental Drift

• Evidence from Landform• Evidence from Fossils• Evidence from Climate

All the continents had once been joined in a single landmass, called Pangaea, and have since drifted apart.

Evidence of Continental Drift A mountain range lines up between Argentina in South America and

Africa. Fossils of the reptiles Mesosaurus and Lystrosaurus have been found in

places now separated by oceans. Fossils of the fernlike plant, Glossopteris, have been found in rocks in

Africa, South America, Australia, India, & Antarctica. Deep scratches in rocks show that continental glaciers once covered South

Africa.

Continental CoastlinesWhy don’t the continents look like they did millions of years ago?

• Coastlines change over time due to beach erosion.

Pangaea

• A supercontinent, meaning “all lands”, that existed about 300 million years ago.

Scientists Reject Wegener’s Hypothesis

• Wegener could not provide a satisfactory explanation for the force that pushes or pull the continents.

Sea-Floor Spreading

Molten material rises from the mantle and erupts along the mid-ocean ridge

Mid-Ocean Ridge

Subduction• Process by which the ocean floor sinks

beneath a deep-ocean trench and back into the mantle.

Plate Tectonics

• Geological theory that states that pieces of Earth's lithosphere are in constant, slow motion

Earthquakes

• Occur usually when 2 plates slide past each other, however, can happen at all plate boundaries.

• Release of energy when the lithosphere suddenly breaks and slides

Convergent Boundaries

• Two plates collide• Example: Himalayan Mountains• Folding mountains, volcanoes, and trenches

can form as a result of plates colliding.

Divergent Boundaries

• Plate boundary where 2 plates move away from each other.

• Is the result of new ocean floor, such as the mid-ocean ridge and valley’s on land.

Transform Boundaries

• Plate boundary where two plates slip past each other, moving in opposite directions.

• Earthquakes frequently occur along these boundaries.

Cause of Deep Ocean Trenches

• When an ocean plate collides with a continental plate, the plate is subducted under the continent.

Ring of Fire

Volcanoes form where tectonic plates meet other plates.

Seismic Waves (PreAP)• Scientists use the properties of waves to study the

internal structure of Earth. Seismic waves are sound waves that may be generated by earthquakes.

• Primary waves, also known as P-waves, are longitudinal waves and can travel through both solids and liquids.

• Secondary waves, also called S-waves, are transverse waves that only travel through solids.

• As these waves pass through the interior of Earth, they change speed or may become refracted or reflected.

Shadow Zone• A wave-free shadow zone exists because the waves are

refracted from their original path as they pass through the boundary between the mantle and the core where they experience changes in density.

Earthquake Epicenter

P- and S- Waves P- and S- Waves

P-Waves only

shadow zoneshadow zone

103 º 103 º

143º 143º