Plate Tectonics

Plate Tectonics

• Theory that states the Earth’s crust is

made of plates that are moving.

• Plates move rafts that float.
• The mantle is part of the Earth’s

interior located beneath the crust.

• Movement of material inside the mantle

causes the plates to move.

• That material is called magma!

Convection Currents

• The magma in the

mantle moves in
currents. The hot
magma will rise
toward the surface
and the cooler magma
will sink.

• This movement causes

the Earth’s crustal
plates to move.

Continental Drift

• Alfred Wegener- Continental drift

IDEA!!

• Continental drift-continents have moved

slowly to their current location but
didn’t explain how.

• Pangaea- “all land”…name given to single

large landmass that was 200 million
years ago.

Evidence of Continental Drift

• Fossil clues
• Climate clues

– Warm weather

plants now found
in colder climates

• Rock clues

– Rock composition
and structure

Seafloor Spreading

• Hot, dense material below Earth’s crust

rises toward the surface.

• This movement causes a mid-ocean ridge

on the sea floor.

• The hot magma causes the plates to

move (or diverge) moving the sea floor
in opposite directions.

Mid-Ocean Ridge

• The mid ocean ridge is the location of

“new Earth” material.

• The magma will cool and form new

crust.

Earth’s Plates

Parts of Earth’s plates:

1.

lithosphere: rigid layer; usually less dense
than the layer beneath it.

2.

Asthenosphere: plastic like layer under
the lithosphere

The rigid plates of the lithosphere
are on top of the plastic like
asthenosphere and move because of
convection currents.

Plate Boundaries

• Movement at plate boundaries cause

changes to Earth’s surface.

• Types of Plate Boundaries:

– Divergent boundaries
– Convergent boundaries
– Transform boundaries (aka strike-slip)

Divergent Boundaries

• When 2 plates move

apart.

• Can form a rift valley

when 2 continental
plates are spread
apart.

• A mid-ocean ridge

can form where
oceanic plates
separate.

• As the magma moves

up, new oceanic crust
is formed.

East

African

Rift
Valley

Convergent Boundary

• When 2 plates collide or move together.
• When 2 oceanic plates collide, one plate

can move underneath another plate.

• This area is called a subduction zone and

can form volcanoes.

• Mountains can also form where

continental plates collide.

Mountains & Volcanoes

Transform Boundary

• Also called Strike-slip fault
• Plates can move in opposite directions or

the same direction.