Plate Tectonics

Theo

ry o

f Co

ntin

enta

l Drif

tProposed by Alfred Wegener in 1912; the hypothesis that state that the continents once formed a single landmass (Pangea), broke up, and drifted to their current location

Weg

ener

’s Ev

iden

ce:

a) Shape of the continents

b) Fossil evidence on both sides of the Atlantic

c) Rock formations on both sides of the Atlantic

d) Climatic evidence (i.e. evidence of glaciers in Southern Africa)

Foss

il Evid

ence

Prob

lem

s with

hi

s The

ory

He could not come up with the mechanisms or process that caused the continents to move

Miss

ing

Evid

ence

: a) Mid-Ocean Ridges – a long undersea mountain chain that has a steep, narrow valley at its center, that forms as magma rises from the mantle, and that creates new ocean floor as the tectonic plates move apart

Miss

ing

Evid

ence

: b) Sea Floor Spreading – the process by which new oceanic crust forms as magma rises to Earth’s surface and solidifies at a mid-ocean ridge, symmetry of rock layers show oldest layers are farther from the ridge

Miss

ing

Evid

ence

: c) Paleomagnetism –• As magma solidifies, iron

particles line up with the Earth’s magnetic field

• Rocks show reversals in the Earth’s Magnetism

• Rocks show symmetrical patterns on both side of the ridges, thus both plates formed at the same time

Pale

omag

netis

m

Plat

e Te

cton

icsThe theory that explains how large pieces of the crust, called plates, move and change shape

Plat

e Te

cton

ics

Lithosphere – solid, outer layer of the Earth that consists of the crust and the rigid upper part of the mantle

Asthenosphere – the solid, plastic layer of the mantle that flows slowly

Tect

onic

Plat

es

15 Major Plates Identified:

Caus

es o

f Pla

te

Motio

n:

Convection – the movement of hot, less dense material up and cold, more dense material down

Mant

le

Conv

ectio

n • Interior of the Earth heats the mantle which rises to the surface at the Mid-Ocean Ridges

• Cools into rock and eventually sinks back into the mantle where it is melted and sinks

• This movement of the mantle drags the plates with it

Plat

e Bo

unda

ries

Dive

rgen

t Bo

unda

ries The boundary between

tectonic plates that are moving away from each other.

Results in: magma rises to surface, forms mid-ocean ridges and rift valleys

Conv

erge

nt

Boun

darie

sThe boundary between tectonic plates that are moving towards each other

Ocea

nic-

Ocea

nic

One plate subducts under the other, forming a trench and melting the plate causing an island arc

Ocea

nic-

Cont

inen

tal

The oceanic plate subducts under the less dense continental plate, the oceanic plate melts, causing volcanoes above

Cont

inen

tal -

Co

ntin

enta

l

Neither plate is dense enough to subduct, thus mountains are built up

Trans

form

Bo

unda

ries

The boundary between two tectonic plates that are sliding past one another, like the San Andreas fault

Earth

quak

esCreated by the sudden movement of tectonic plates, typically occur along plate boundaries

Volca

noes Places where magma

erupts from the surface

Ring

of F

ire

An area around the Pacific Ocean characterized by volcanoes and seismic activity

Hot S

pots

Areas where magma reaches the surface, the source is under the plates so the hot spot does not move, but the plates do, creates island arcs like Hawaii