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.