Plate Tectonics

Theory

of

Conti

nenta

l Dri

ft Proposed 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

Wegener’

s Evi

dence

:

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 Evi

dence

Proble

ms

wit

h

his

Theory

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

Mis

sing

Evi

dence

: 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

Mis

sing

Evi

dence

: 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

Mis

sing

Evi

dence

:

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

om

agneti

sm

Pla

te T

ect

onic

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

Pla

te T

ect

onic

s 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

Pla

tes

15 Major Plates Identified:

Cause

s of

Pla

te

Moti

on:

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

Mantl

e

Conve

ctio

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

Pla

te B

oundari

es

Div

erg

ent

Boundari

es 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

Conve

rgent

Boundari

es

The boundary between tectonic plates that are moving towards each other

Oce

anic

-Oce

anic

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

Oce

anic

-C

onti

nenta

l

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

Conti

nenta

l -

Conti

nenta

l

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

Transf

orm

B

oundari

es

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

Eart

hquake

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

Volc

anoes

Places where magma erupts from the surface

Rin

g o

f Fi

re

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

Hot

Spots

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