1

ESS

200A

Pro

f. J

in-Y

i Yu

Lec

ture

6: S

olid

Ear

th (

Out

line)

Clim

ate

Rol

e of

the

Solid

Ear

th

Inte

rnal

Str

uctu

re o

f th

e So

lid E

arth

The

ory

of P

late

Tec

toni

cs

His

tory

of

Pla

te T

ecto

nics

Fro

mT

he B

lue

Pla

net

ESS

200A

Pro

f. J

in-Y

i Yu

Pla

te T

ecto

nics

and

Clim

ate

(fro

m E

arth

’s C

lim

ate:

Pas

t and

Fut

ure)

How

can

one

acc

ount

for

the

alte

rnat

ing

peri

ods

of c

limat

ic w

arm

th a

nd

cool

ness

obs

erve

d in

the

geol

ogic

rec

ord?

Par

t of

the

answ

er m

ust l

ie in

the

tect

onic

act

ivity

and

the

posi

tions

of

the

cont

inen

ts.

ESS

200A

Pro

f. J

in-Y

i Yu

Tec

toni

c-S

cale

Cli

mat

e C

hang

e

The

fai

nt y

oung

Sun

pa

rado

x an

d its

pos

sibl

e ex

plan

atio

n.

Why

was

Ear

th ic

e-fr

ee

even

at t

he p

oles

100

Myr

ag

o (t

he M

esoz

oic

Era

)?

Wha

t cau

sed

Ear

th’s

cl

imat

e to

coo

l ove

r th

e la

st 5

5 M

yr(t

he C

enoz

oic

Era

)?

Ice-

free

Ear

th

(fro

m E

arth

’s C

lim

ate:

Pas

t and

Fut

ure)

ESS

200A

Pro

f. J

in-Y

i Yu

Pla

te T

ecto

nics

Con

tine

ntal

Dri

ftin

g T

heor

yA

lfre

d W

egen

er p

ropo

sed

that

all

the

cont

inen

ts

wer

e on

ce a

ssem

bled

into

a s

uper

cont

inen

t (P

ange

a) a

nd th

en b

roke

and

slo

wly

dri

fted

to th

eir

curr

ent p

ositi

ons.

Pla

te T

ecto

nics

The

bra

nch

of te

cton

ics

that

dea

ls w

ith

the

proc

esse

s by

whi

ch th

e lit

hosp

here

pla

tes

mov

e an

d in

tera

ct w

ith e

ach

othe

r is

cal

led

plat

e te

cton

ics.

2

ESS

200A

Pro

f. J

in-Y

i Yu

Cir

cula

tion

of th

e So

lid E

arth

Col

d L

ithos

pher

e

Fro

mT

he B

lue

Pla

net

The

ris

ing

hot r

ocks

and

slid

-aw

ay f

low

s ar

e th

ough

t to

be th

e fa

ctor

th

at c

ontr

ol th

e po

sitio

ns o

f oc

ean

basi

ns a

nd c

ontin

ents

.

The

con

vect

ion

dete

rmin

es th

e sh

ape

of th

e E

arth

.E

SS20

0AP

rof.

Jin

-Yi Y

u

Tw

enty

Rig

id P

late

s

Wha

t can

hap

pen

to th

e co

ld b

ound

ary?

The

lith

osph

ere

has

brok

en in

to a

num

ber o

f ro

cky

piec

es, c

alle

dpl

ates

.

The

re a

re a

few

larg

e pl

ates

plu

s a

num

ber

of s

mal

ler

one

com

pris

e th

e E

arth

’s s

urfa

ce (

a to

tal o

f 20

pla

tes)

.

The

pla

tes

rang

e fr

om s

ever

al h

undr

ed to

sev

eral

thou

sand

kilo

met

ers

in

wid

th.

Fro

mT

he B

lue

Pla

net

ESS

200A

Pro

f. J

in-Y

i Yu

Con

tinen

tal a

nd O

cean

ic C

rust

s

Som

e lit

hosp

heri

cpl

ates

are

com

pose

d pr

imar

ily

of

ocea

nic

crus

tal m

ater

ial,

whe

reas

oth

ers

are

com

pose

d pr

imar

ily o

f co

ntin

enta

l mat

eria

ls.

The

con

tinen

ts s

tand

, on

aver

age,

abo

ut 4

.5 k

m

abov

e th

e fl

oor

of th

e oc

ean

basi

ns.

Con

tine

ntal

cru

st is

rel

ativ

ely

ligh

t (de

nsit

y 2.

7

g/cm

3), w

here

as o

cean

ic c

rust

is r

elat

ivel

y he

avy

(den

sity

clo

se to

3.2

g/c

m3)

.E

SS20

0AP

rof.

Jin

-Yi Y

u

Tem

pera

ture

Str

uctu

res

in th

e So

lid E

arth

Fro

mT

he B

lue

Pla

net

The

lith

osph

eric

pla

tes

are

ridi

ng o

n to

p of

a la

yer

of h

ot, d

uctil

e, e

asily

de

form

ed m

ater

ial c

alle

d th

e as

then

osph

ere,

or

“wea

k la

yer”

.

Hea

t mov

es b

y co

nduc

tion

abov

e 10

0 km

and

by

conv

ectio

n be

low

100

km

.

Tem

pera

ture

at t

he c

ente

r of

the

eart

h is

bel

ieve

d to

clo

se to

500

0ºC

.

3

ESS

200A

Pro

f. J

in-Y

i Yu

Hea

t In

Ear

th’s

Int

erio

r

The

re a

re tw

o m

ajor

sou

rces

of

the

heat

in E

arth

’s

inte

rior

:

(1)

Rad

ioac

tive

deca

y: o

f po

tass

ium

, ura

nium

, and

th

oriu

m.

(2)

Res

idua

l hea

t fro

m E

arth

’s f

orm

atio

n: A

tr

emen

dous

am

ount

of

ener

gy w

as tr

ansf

erre

d to

Ear

th

duri

ng th

e ac

cret

ion

of th

e pl

anet

by

colli

sion

s w

ith

plan

etes

imal

s.

ESS

200A

Pro

f. J

in-Y

i Yu

The

The

ory

of P

late

Tec

toni

cs

A m

ajor

pro

blem

of

the

cont

inen

t dri

ftin

g th

eory

is: H

ow c

ould

the

cont

inen

ts d

rift

th

roug

h th

e ri

gid

sea

floo

r?

Thi

s pr

oble

m is

ans

wer

ed b

y th

e se

aflo

or

spre

adin

g hy

poth

esis

: Con

tine

nts

do n

ot p

low

th

roug

h th

e se

a fl

oor.

Con

tine

nts

and

segm

ents

of

oce

an fl

oor

are

conn

ecte

d in

to p

late

s th

at

cont

inuo

usly

mov

e aw

ay fr

om o

ne a

noth

er a

t m

id-o

cean

rid

ges.

ESS

200A

Pro

f. J

in-Y

i Yu

Sea

floo

r S

prea

ding

(fro

mT

he e

arth

Sys

tem

)

ESS

200A

Pro

f. J

in-Y

i Yu

Pla

te M

argi

nsIn

tera

ctio

ns b

etw

een

plat

es o

ccur

alo

ng

thei

r ed

ges.

The

re a

re th

ree

type

s of

pla

te

mar

gins

:

(1)

Div

erge

nt m

argi

ns

form

mid

-oce

an r

idge

s (o

ver

ocea

ns)

and

rift

val

leys

(ov

er la

nds)

(2)

Con

verg

ent m

argi

ns

form

dee

p-se

a tr

ench

es (

two

ocea

nic

plat

es

or o

cean

+con

tinen

tal p

late

s) o

r hi

gh

mou

ntai

ns (

such

as

Tib

etan

Pla

teau

) (t

wo

cont

inen

tal p

late

s).

(3)

Tra

nsfo

rm f

ault

mar

gins

form

ear

thqu

ake

faul

ts

Fro

mT

he B

lue

Pla

net

4

ESS

200A

Pro

f. J

in-Y

i Yu

Thr

ee W

ays

for

Solid

Ear

th to

Aff

ect C

lim

ate

Pol

ar p

osit

ion

hypo

thes

is

Che

mic

al W

eath

erin

g H

ypot

hesi

s

Seaf

loor

Spr

eadi

ng H

ypot

hesi

s

ESS

200A

Pro

f. J

in-Y

i Yu

The

Pol

ar P

ositi

on H

ypot

hesi

s

The

pol

ar p

ositi

on h

ypot

hesi

s fo

cuse

d on

la

titu

dina

l pos

ition

as

a ca

use

of g

laci

atio

n of

co

ntin

ents

.

Thi

s hy

poth

esis

sug

gest

ed th

at ic

e sh

eets

sh

ould

app

ear

on c

ontin

ents

whe

n th

ey a

re

loca

ted

at p

olar

or

near

-pol

ar la

titu

des.

To

expl

ain

the

occu

rren

ce o

f ice

hous

e in

terv

als,

this

hyp

othe

sis

call

s no

t on

wor

ldw

ide

clim

ate

chan

ges

but s

impl

y on

the

mov

emen

ts o

f con

tinen

ts o

n te

cton

ic p

late

s.

Thi

s hy

poth

esis

can

not

exp

lain

the

clim

ate

of th

e L

ate

Prot

eroz

oic

Era

, whe

n bo

th

cont

inen

ts a

nd g

laci

ers

appe

ar to

hav

e be

en

situ

ated

at r

elat

ivel

y lo

w la

titu

des.

It c

an n

ot e

xpla

in th

e w

arm

Mes

ozoi

c E

ra

whe

n hi

gh-l

atitu

de c

ontin

ents

wer

e pr

esen

t bu

t wer

e al

mos

t com

plet

ely

ice-

free

.(f

rom

Ear

th’s

Cli

mat

e: P

ast a

nd F

utur

e)

ESS

200A

Pro

f. J

in-Y

i Yu

Clim

ate

Cha

nges

in th

e L

ast 5

00 M

yr

Clim

ate

in th

e pa

st 5

00 m

illio

n ye

ars

have

alte

rnat

ed b

etw

een

long

pe

riod

s of

war

m c

limat

e an

d sh

ort p

erio

ds o

f co

ld c

limat

e.

Dur

ing

the

last

500

mill

ion

year

s, m

ajor

con

tinen

t-si

ze ic

e sh

eets

ex

iste

d on

Ear

th d

urin

g th

ree

iceh

ouse

ear

: (1)

a b

rief

inte

rval

near

430

M

yr a

go, (

2) a

muc

h lo

nger

inte

rval

fro

m 3

25 to

240

Myr

ago

, and

(3)

th

e cu

rren

t ice

hous

e er

a of

the

last

35

mill

ion

year

.

(fro

m E

arth

’s C

lim

ate:

Pas

t and

Fut

ure)

ESS

200A

Pro

f. J

in-Y

i Yu

Che

mic

al W

eath

erin

gT

he p

reci

pita

tion

proc

ess

in th

e at

mos

pher

e di

ssol

ve a

nd r

emov

e C

O2

from

the

atm

osph

ere.

Roc

ks e

xpos

ed a

t Ear

th’s

sur

face

un

derg

o ch

emic

al a

ttac

k fr

om th

is

rain

of

dilu

te a

cid.

Thi

s w

hole

pro

cess

is k

now

n as

ch

emic

al w

eath

erin

g.

The

rat

e of

che

mic

al w

eath

erin

g te

nd

to in

crea

se a

s te

mpe

ratu

re in

crea

ses.

Wea

ther

ing

requ

ires

wat

er a

s a

med

ium

bot

h fo

r th

e di

ssol

utio

n of

m

iner

als

and

for

the

tran

spor

t of

the

diss

olve

d m

ater

ials

to th

e oc

ean

The

rat

e of

che

mic

al w

eath

erin

g in

crea

ses

as p

reci

pita

tion

incr

ease

s.

(fro

m E

arth

’s C

lim

ate:

Pas

t and

Fut

ure)

5

ESS

200A

Pro

f. J

in-Y

i Yu

Neg

ativ

e Fe

edba

ck F

rom

Che

mic

al W

eath

erin

g

The

che

mic

al w

eath

erin

g w

orks

as

a ne

gati

ve

feed

back

that

mod

erat

es

long

-ter

m c

limat

e ch

ange

.

Thi

s ne

gati

ve f

eedb

ack

mec

hani

sm li

nks

CO

2le

vel i

n th

e at

mos

pher

e to

the

tem

pera

ture

and

pr

ecip

itatio

n of

the

atm

osph

ere.

(fro

m E

arth

’s C

lim

ate:

Pas

t and

Fut

ure)

ESS

200A

Pro

f. J

in-Y

i Yu

Ear

th’s

The

rmos

tat –

Che

mic

al W

eath

erin

g

Che

mic

al w

eath

erin

g ac

ts a

s E

arth

’s th

erm

osta

t an

d re

gula

te it

s lo

ng-t

erm

clim

ate.

Thi

s th

erm

osta

t mec

hani

sm

lies

in tw

o fa

cts:

(1

) th

e av

erag

e gl

obal

rat

e of

ch

emic

al w

eath

erin

g de

pend

s on

the

stat

e of

Ear

th’s

clim

ate,

(2

) w

eath

erin

g al

so h

as th

e ca

paci

ty to

alte

r th

at s

tate

by

regu

latin

g th

e ra

te w

hich

CO

2is

rem

oved

fro

m th

e at

mos

pher

e.(f

rom

Ear

th’s

Cli

mat

e: P

ast a

nd F

utur

e)

ESS

200A

Pro

f. J

in-Y

i Yu

Fain

t You

ng S

un P

arad

ox

Sola

r lu

min

osit

y w

as m

uch

wea

ker

(~30

%)

in th

e ea

rly

part

of

Ear

th’s

his

tory

(a

fain

t you

ng

Sun)

.

If E

arth

’s a

lbed

o an

d gr

eenh

ouse

ef

fect

rem

aine

d un

chan

ged

at th

at

time,

Ear

th’s

mea

n su

rfac

e te

mpe

ratu

re w

ould

be

wel

l bel

ow

the

free

zing

poi

nt o

f w

ater

dur

ing

a la

rge

port

ion

of it

s 4.

5 B

yrhi

stor

y.

Tha

t wou

ld r

esul

t in

a “s

now

ball”

Ear

th, w

hich

was

not

evi

dent

in

geol

ogic

rec

ord.

(fro

m T

he E

arth

Sys

tem

)E

SS20

0AP

rof.

Jin

-Yi Y

u

Tec

toni

c C

ontr

ol o

f C

O2

Inpu

t–T

he S

eafl

oor

Spre

adin

g R

ate

Hyp

othe

sis

Dur

ing

activ

e pl

ate

tect

onic

pro

cess

es, c

arbo

n cy

cles

con

stan

tly

betw

een

Ear

th’s

inte

rior

and

its

surf

ace.

The

car

bon

mov

es f

rom

dee

p ro

ck r

eser

voir

s to

th

e su

rfac

e m

ainl

y as

CO

2ga

s as

soci

ated

with

vo

lcan

ic a

ctiv

ity a

long

the

mar

gins

of

Ear

th’s

te

cton

ic p

late

s.

The

cen

terp

iece

of

the

seaf

loor

spr

eadi

ng

hypo

thes

is is

the

conc

ept t

hat c

hang

es in

the

rate

of

sea

floo

r sp

read

ing

over

mill

ions

of

year

s co

ntro

l the

rat

e of

del

iver

y of

CO

2to

the

atm

osph

ere

from

the

larg

e ro

ck r

eser

voir

of

carb

on, w

ith th

e re

sulti

ng c

hang

es in

atm

osph

eric

C

O2

conc

entr

atio

ns c

ontr

ollin

g E

arth

’s c

lim

ate.

(fro

m E

arth

’s C

lim

ate:

Pas

t and

Fut

ure)

6

ESS

200A

Pro

f. J

in-Y

i Yu

Tec

toni

c C

ontr

ol o

f C

O2

Rem

oval

–T

he

Upl

ift W

eath

erin

g H

ypot

hesi

s

The

upl

iftin

g w

eath

erin

g hy

poth

esis

as

sert

s th

at th

e gl

obal

mea

n ra

te o

f ch

emic

al w

eath

erin

g is

hea

vily

aff

ecte

d by

the

avai

labi

lity

of f

resh

roc

k an

d m

iner

al s

urfa

ces

that

the

wea

ther

ing

proc

ess

can

atta

ck.

Thi

s hy

poth

esis

sug

gest

s th

at te

cton

ic

uplif

ting

enha

nces

the

expo

sure

of

fres

hly

frag

men

ted

rock

whi

ch is

an

impo

rtan

t fac

tor

in th

e in

tens

ity

of

chem

ical

wea

ther

ing.

Thi

s hy

poth

esis

look

s at

che

mic

al

wea

ther

ing

as th

e ac

tive

driv

er o

f cl

imat

e ch

ange

, rat

her

than

as

a ne

gativ

e fe

edba

ck th

at m

oder

ates

clim

ate

chan

ges.

(fro

m E

arth

’s C

lim

ate:

Pas

t and

Fut

ure)

ESS

200A

Pro

f. J

in-Y

i Yu

Can

The

se T

wo

Hyp

othe

ses

Exp

lain

T

ecto

nic-

Scal

e C

limat

e C

hang

es?

(fro

m E

arth

’s C

lim

ate:

Pas

t and

Fut

ure)