PLATE TECTONICS, EARTHQUAKES, AND THE STRUCTURE OF THE EARTH

GOALS FOR THE LECTURE• Students will write and discuss various ideas

related to the physical structure of the Earth (9C, 10A, 10B, 10C, 10E, 10F)

• Students will write and discuss ideas related to plate tectonics, as well as follow its progression through history(10D)

WHY DOES THE EARTH LOOK LIKE THIS?• Where did the tectonic plates come from?• They came from the ancient land masses the used

to cover the Earth

HISTORY• Has the Earth always looked like this?• What did the Earth look like in the past?

HISTORY• What name do we give this place?• Pangea

• When was this?• 200 million years ago (mya)

• Before there was Pangea, the Earth looked even less like it does today

HISTORY• About 160 mya, Pangea began to break apart.• Laurasia and Gondwanaland were the dominant

land features.

HISTORY• About 120 mya, Laurasia and

Gondwanaland began to break apart. • Continents we might recognize were the

result.

HISTORY• 80 mya, Madagascar breaks off from India

as India begins its race across the Indian Ocean.

HISTORY• 40 mya, Inland seas in the North American

Plate and Asian plates drained and India began to push up the Himalayan mountains.

TODAY

FOSSIL EVIDENCE• Organisms have left fossil evidence of their

existence on continents across oceans. • Originally thought to be caused by

organisms traveling across the ocean on “Rafts.”

FOSSIL EVIDENCE• Other theories suggested organisms crossed

over land bridges that were once exposed.

FOSSIL EVIDENCE• A 3rd theory surfaced known as Island

stepping stones.

EVIDENCE THAT THIS IS WHAT REALLY HAPPENED…

CONTINENTAL DRIFT• Alfred Wegener publishes The Origin of

Continents and Oceans in 1915.• Proposes that the continents were once all

part of a large landmass called Pangea, and then drifted apart.

CONTINENTAL DRIFT• This idea matured into our current theories

of Plate Tectonics• The surface of the earth is divided into

about 20 plates.

PLATE TECTONICS• All plates contain both continental and

oceanic crust.• This is a major departure from continental

drift.

THE THEORY• Plates are rigid structures and will always

move as a distinct unit.• The distance between two points on a tectonic

plate will always be the same

LITHOSPHERE• The layer of solid rock that surrounds the

Earth and a thin layer of molten rock beneath it.

ASTHENOSPHERE• The molten rock beneath the lithosphere.

WHERE DO THINGS CHANGE?• At the boundaries between plates.• 3 categories

• Divergent• Convergent• Transform

DIVERGENT

WAIT NO…

DIVERGENT BOUNDARIES• Occur at oceanic spreading centers,

typically called “Mid-Ocean Ridges”• 2 “Plates” are being pulled apart by magma

from underneath that is pushing upwards• Process known as Seafloor Spreading

CONVERGENT BOUNDARIES• 3 classifications of Convergent Boundaries• Oceanic-Continental• Oceanic-Oceanic• Continental-Continental

CONVERGENT BOUNDARIES• Subduction Zone(vocabulary)- the place

where one tectonic plate rides up over another and causes it to be pushed down and recycled (melted)

CONVERGENT BOUNDARIES• Oceanic-Continental• Result in the formation of Volcanic Arcs along the

boundary

CONVERGENT BOUNDARIES• Oceanic-Oceanic• Result in the formation of Island Arcs• Chains of volcanic islands that form along oceanic

plate boundaries

CONVERGENT BOUNDARIES• Oceanic-Oceanic boundaries will also result

in the formation of Trenches• These are places where the ocean is deeper

than the surrounding area due to subduction.

CONVERGENT BOUNDARIES• Continental-Continental• Result in the formation of mountain ranges

made from deformed (squeezed) native rock

CONVERGENT BOUNDARIES

TRANSFORM BOUNDARIES• Plates move in opposing directions on either

side of the boundary.