Chapter 9: Plate Tectonics Review

Layers of the Earth

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

Layers of the Earth

Temp.(°C)

Elements

Crust 0- 860 Oxygen, silicon

Mantle 870 Iron, magnesium

OuterCore

2200 Iron, nickel

InnerCore

5000 iron

Lithosphere

• The cool, rigid layer of the crust and upper most solid mantle.

• 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.

Convection

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

• This is also true with air and other fluids.

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.

Pangaea

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

Plate Tectonics

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

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 rift valley’s on land.

Sea-Floor Spreading

Molten material rises from the mantle and erupts along the Mid-Atlantic ridge

Image: A diver swims between the Eurasian and North American plates in Thingvellir lake, Thingvellir National Park, Iceland. Iceland is one place where a mid-ocean ridge can be seen on land and in shallow waters.(credit: Wild Wonders of Europe/Lundgre

http://www.bbc.co.uk/science/earth/surface_and_interior/mid_ocean_ridge

Convergent Boundaries• Two plates move towards each other and collide.• The result can be an ocean trench, island arc,

volcanoes, and mountain ranges.

Cause of Deep Ocean Trenches

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

• Subduction - Process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Folded Mountains

• When 2 continental plates collide, folding mountains occur

Himalayans from space

Transform Boundaries

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

• Earthquakes frequently occur along these boundaries.

• Creates a fault

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

Ring of Fire

Volcanoes form where tectonic plates meet other plates.