Plate Tectonics

Chapter 5

Earth’s Interior

• Scientists learn about the interior of Earth in 2 ways

–Direct Method

•Rock Samples

–Drilling

–Caves

Earth’s Interior

–Indirect Method

•Seismic Waves

–Speed of waves and paths shows the structure of the planet

»Show that the earth is made up of several layers

Seismic

Waves

The Layers of the earth vary in

several ways

• Temperature

–Gets warmer as you descend toward the center of the earth

•Temperature rises 1oC for every 40 meters descended

• Pressure

–Pressure increases as you descend

The Layers of the Earth

The Crust

• The Crust

–Outer Layer

•Includes dry land

•Includes the ocean floor

•Includes Water and soil

The Crust

–Thinner than other layers

•Thinnest under oceans

–Called oceanic crust

»Composed of BASALT

•Thickest under mountains

–Called continental crust

»Composed of Granite

The Mantle

–40 Km below surface

–Hot Solid Rock

–About 3000 km thick

The Mantle

–Divided into layers

•Lithosphere

–Upper part of mantle

–Rigid Layer

The Mantle

•Asthenosphere

–Below lithosphere

–Hotter

–Increasing pressure

–Softer but still solid

The Mantle

•Lower Mantle

–Under Asthenosphere

–Solid- extends to the core

The Core

–Made of iron and Nickel

–Has 2 parts

• Outer Core

–Liquid

–Molten(melted) metal surrounding inner core

• Inner Core

–Dense ball

–Solid metal

The Core

–Creates a Magnetic Field

•Due to movement in the core

•Magnetic poles

Types of Heat Transfer

• Radiation: transfer of energy through space

–No direct contact between heat source and object

–Examples

•The sun

•Fire

Types of Heat Transfer

• Conduction: heat transfer withina material or between materials that are touchingResponsible for some of the heat transfer within the EarthExample: metal spoonin a hot pot

Types of Heat Transfer

• Convection: heat transfer by the movement of currents in a fluid–Caused by differences in

temperature and densities in a fluid

–Examples• Convection zone in the sun

• Deep currents in ocean

Convection Currents

in the Earth

• Mantle–Heat from the mantle causes

convection current• Moves the plates of the lithosphere

• Core–Heat in the outer (liquid) core causes a

convection current• Causes Earth’s magnetic field

Continental Drift

• Alfred Wegner

–Thought all continents formed Pangaea at one time

• Pangaea: a single land mass

• Evidence

–Shape of the continents

–Fossils

»Glossopteris

–Climate

Continental Drift

–Wegener’s theory was rejected

•He could not explain the forces that push and pull the continents

Seafloor Spreading

• Mid Ocean Ridges

• Tall mountain ridges hidden under the oceans

–Curve around the world

•In a few places the ridge or mountain is above the surface of the ocean

• Example: Iceland

Mid Ocean Ridges

• Mapped using Sonar

–Sonar is a device that bounces sound waves off underwater objects and then records the echoes of the sound waves

Sea Floor Spreading

• Sea floor spreads apart along both sides of the mid ocean ridge

–Adds New Crust

–Ocean floor like a conveyor belt

•Carries continents

Evidence of Sea Floor Spreading

–Molten material

•Submarine Alvin finds pillow shaped rocks

–These rocks only form when molten material cools quickly

–Magnetic strips

•The earth’s magnetic poles have reversed many times

–Evidence in the rocks on the ocean floor

Evidence of Sea Floor Spreading

Magnetic Stripes

–Drilling Samples

•The samples far from the ridge are older

•The “youngest” rocks near the center of the ridge

Evidence of Sea Floor Spreading

Subduction at Trenches

• Process by which ocean floor sinks under the trench and back into the mantle

–Crust near ridge moves awayfrom ridge

•Like a giant conveyor belt

Subduction at the Trenches

• The ocean floor

–Pacific Ocean is shrinking

•Lots of deep trenches

–Trench swallows more of the floor faster than its made

–Atlantic Ocean expanding

•Oceanic crust attached to the continental crust

–Continents move

Theory of Plate

Tectonics

• J. Tuzo Wilson

• Scientist who discovered the plates

–Plates: a section of the lithosphere that slowly movesover the Asthenospherecarrying pieces of the continental and oceanic crust

Theory of Plate Tectonics

• Combined continental drift and sea floor spreading into a scientific theory

–Scientific Theory: well testedconcept that explains a wide range of observations

•Ideas that are supported by data.

How Plates Move

• Theory of Plate Tectonics–Earth’s lithosphere is in constant, slow motion driven by the convection currents in the mantle.

3 ways of moving

–Collide (convergent)

–Pull apart (divergent)

–Grind past each other (transform)

•Each changes the earth’s

surface

Plate Boundaries

• Extend deep into the lithosphere

–Faults: breaks in Earth’s crust where rocks have slipped past each other

•Move Slowly

3 types of Boundaries

•Divergent (Move apart)

•Convergent (Collide)

•Transform (Move past)

Divergent Boundaries

–Plates move away from each other

–Most occur along the mid ocean ridge

•Where sea floor spreading occurs

–Can occur on land

•Forms a Rift Valley

• A deep valley

Convergent Boundaries

–Two plates that come together or collide

–Density of the plates determine which plate is on top

•Oceanic crust vs. continental crust

–Subduction.

• Continental crust vs. continentalcrust

• Mountains are squeezed from the crust

Transform Boundaries

–2 plates slip past each other

•Earthquakes are common

–Crust is neither destroyedor created