Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Ast

rono

my

210

Sect

ion

1–M

WF

150

0-15

5013

4 A

stro

nom

y B

uild

ing

Thi

s C

lass

(L

ectu

re 1

9):

The

Ear

th

Nex

t Cla

ss:

The

Ear

th-M

oon

Syst

em

Mus

ic: A

my

Hit

the

Atm

osph

ere

–C

ount

ing

Cro

ws

Nig

ht O

bser

vatio

ns!

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Out

line

•T

he B

lue

Bal

l.

•D

iffe

rent

iatio

n of

the

earl

y E

arth

.

•E

arth

’s s

truc

ture

.

•T

he E

arth

’s a

tmos

pher

e.

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

The

Sol

ar S

yste

m is

Our

s!

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Rad

ius

6378

km

Surf

ace

grav

ity9.

8 m

/s2

Mas

s6.

0x10

24kg

Avg.

Den

sity

5500

kg/

m3

Dis

tanc

e fr

om S

un1.

5x10

8km

Year

365.

2422

day

sSo

lar

day

1 da

y

The

Ear

th –

Fas

t Fac

ts

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Easi

ly g

et t

he M

ass

from

g=

GM

/R2

Then

the

ave

rage

den

sity

is

ρ=

3/4π

M/R

3=

550

0 kg

/m3

This

is b

etw

een

rock

and

iron

, so

som

e of

eac

h.

The

Ear

th –

Fas

t Fac

ts

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Dif

fere

ntia

tion

•A

vera

ge d

ensi

ty o

f E

arth

is

5.5

g/c

m3

•A

vera

ge d

ensi

ty o

n th

e su

rfac

e is

3 g

/cm

3

•So

, som

ethi

ng h

eavy

m

ust b

e in

side

•W

hen

the

Ear

th f

orm

ed

it w

as m

olte

n–

Hea

vy m

ater

ials

(e.

g. ir

on,

nick

el, g

old)

san

k–

Lig

hter

mat

eria

ls (

e.g.

sili

con,

oxy

gen)

flo

ated

to th

e to

p

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Plan

etar

y D

iffe

rent

iatio

n

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Stru

ctur

e•

Luc

kily

, not

all

of

the

iron

san

k to

th

e ce

nter

, els

e w

e w

ould

be

still

in

the

Ston

e A

ge.

•C

ore

is m

ade

of 2

par

ts–

inne

r co

re

and

the

oute

r co

re.

•T

empe

ratu

re in

crea

ses

as y

ou g

o de

eper

. Fr

om a

roun

d 29

0 K

on

surf

ace

to n

earl

y 50

00 K

at c

ente

r.

–H

eate

d by

rad

ioac

tive

deca

y

•T

he d

eepe

r yo

u go

, mor

e pr

essu

re

from

mas

s of

Ear

th.

•M

ass

of th

e co

re =

1/3

Ear

th’s

m

ass

and

near

ly h

alf

the

radi

us.

Cru

st

Man

tle

Out

er C

ore

Inne

r C

ore

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Inne

r C

ore

•R

each

es v

ery

high

tem

pera

ture

s–50

00 K

(C

lose

to th

e te

mpe

ratu

re a

t the

sur

face

of

the

Sun)

!

•B

ut s

till t

he h

igh

pres

sure

mak

es th

e in

ner

core

rem

ains

a

solid

–

Soli

d in

ner

core

–12

00 k

m r

adiu

s

•M

ostly

mad

e of

iron

(Fe

) an

d ni

ckel

(N

i)

•In

form

atio

n ab

out t

he in

ner

core

com

es f

rom

the

stud

y of

ea

rthq

uake

s, m

eteo

rite

s an

d th

e E

arth

’s m

agne

tic f

ield

.

•M

ight

be

rota

ting

fast

er th

an th

e re

st o

f th

e pl

anet

.

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Out

er C

ore

•T

he li

quid

laye

r of

the

Ear

th,

high

pre

ssur

e bu

t not

eno

ugh

to

solid

ify

–L

iqui

d ou

ter

core

–22

00 k

m

radi

us

•M

ostly

Fe

and

Ni.

•M

ade

of v

ery

hot m

olte

n liq

uid

that

flo

ats

and

flow

s ar

ound

the

soli

d in

ner

core

–cr

eate

s th

e E

arth

’s m

agne

tic f

ield

.

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

The

Man

tle

•L

arge

st la

yer

of th

e E

arth

–T

o a

dept

h of

290

0 km

–T

empe

ratu

re in

crea

ses

with

dep

th

–M

ade

of h

eavy

sili

cate

s

•Pa

rts

of th

e m

antle

are

hot

eno

ugh

to

have

an

oozi

ng, p

last

ic f

low

–So

rt o

f lik

e Si

lly P

utty

–C

urre

nts

in th

e m

antle

cau

se p

late

tect

onic

s

–H

ot s

pots

in th

e m

antle

can

bec

ome

plum

es o

f m

agm

a (e

.g.,

the

Haw

aiia

n Is

land

s)

http

://w

ww

.mar

tysp

sagr

aded

card

s.co

m/6

1mm

.jpg

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

The

Cru

st•

Out

side

laye

r of

the

Ear

th (

incl

udes

oce

ans)

that

fl

oats

on

top

–A

bout

50

km th

ick

–C

olde

st la

yer

–ro

cks

are

rigi

d

•M

ostly

sili

cate

roc

ks–

Mad

e of

ligh

ter

elem

ents

like

sili

con,

oxy

gen,

and

al

umin

um

•O

xyge

n an

d w

ater

are

abu

ndan

t

•E

xcel

lent

insu

lato

r–

Kee

ps th

e E

arth

’s g

eoth

erm

al h

eat

insi

de!

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Ear

th's

Sur

face

•70

% o

f th

e E

arth

's

surf

ace

is c

over

ed

with

wat

er–

Oce

an b

asin

s

–Se

a fl

oors

are

you

ng,

none

mor

e th

an

200

mill

ion

year

s ol

d

•30

% is

dry

land

–C

ontin

ents

–M

ixtu

re o

f yo

ung

rock

s an

d ol

d ro

cks

–U

p to

4.2

bill

ion

year

s ol

d

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Geo

logi

cally

Act

ive

Surf

ace

•T

he y

oung

roc

ks o

n th

e E

arth

's s

urfa

ce

indi

cate

it is

ge

olog

ical

ly a

ctiv

e•

Whe

re d

o th

ese

rock

s co

me

from

?–

Vol

cano

es–

Rif

t val

leys

–O

cean

ic r

idge

s

•A

ir, w

ater

ero

de r

ocks

•T

he s

urfa

ce is

con

stan

tly

chan

ging

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Ear

thqu

ake

Act

ivity

http

://ne

ic.u

sgs.

gov/

neis

/gen

eral

/sei

smic

ity/

wor

ld.h

tml

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Vol

cano

es

http

://w

ww

.vol

cano

.si.e

du/w

orld

/loca

tion.

cfm

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Pla

te T

ecto

nics

•T

he E

arth

’s s

urfa

ce is

bro

ken

up in

to a

bout

a d

ozen

“pl

ates

”•

Plat

es “

floa

t” o

n de

nser

roc

k be

low

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Con

tinen

tal D

rift

•Y

ou m

ight

thin

k th

at

Sout

h A

mer

ica

and

Afr

ica

“fit”

like

a

jigsa

w p

uzzl

e

•T

his

gave

ris

e to

the

idea

of

cont

inen

tal d

rift

•In

the

1950

s, th

e di

scov

ery

of u

nder

wat

er

mou

ntai

n ri

dges

con

firm

ed th

e id

ea

•T

he s

eafl

oor

betw

een

the

Nor

th A

mer

ica

and

Eur

ope/

Afr

ica

is s

prea

ding

at 3

cm p

er y

ear!

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

How

Pla

te T

ecto

nics

Wor

ks

•C

urre

nts

in th

e de

nser

roc

k sq

ueez

e, p

ull,

brea

k,

and

stre

tch

the

Ear

th's

sur

face

–St

ress

es b

uild

up

betw

een

the

plat

es•

Rel

ease

d in

the

form

of

eart

hqua

kes

–B

reak

s in

the

plat

es a

llow

mag

ma

to f

low

up

•C

reat

es v

olca

noes

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Mov

ing

Ear

th

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Pla

te T

ecto

nics

in A

ctio

n

Seaf

loor

Spr

eadi

ngPl

ate

Subd

uctio

n

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Pud

ding

Pro

of

http

://w

ww

.ear

th.n

orth

wes

tern

.edu

/peo

ple/

seth

/107

/Pla

tem

otio

n/vl

bi.h

tmht

tp://

kids

.ear

th.n

asa.

gov/

arch

ive/

pang

aea/

SL

R.J

PG

http

://w

ww

.ear

th.n

orth

wes

tern

.edu

/peo

ple/

seth

/107

/Int

ro/s

afpa

lmda

le.h

tml

http

://ki

ds.e

arth

.nas

a.go

v/ar

chiv

e/pa

ngae

a/ev

iden

ce.h

tml

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Pla

te T

ecto

nics

in A

ctio

n

Seaf

loor

Spr

eadi

ngPl

ate

Subd

uctio

n

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Rec

yclin

g B

io-e

lem

ents

•Fr

om g

ravi

ty a

nd r

adio

activ

ity, t

he c

ore

stay

s ho

t.•

Thi

s al

low

s a

pers

istin

g ci

rcul

atio

n of

bio

elem

ents

thro

ugh

cont

inen

tal d

rift

—m

eltin

g of

the

crus

t and

re-

rele

ase

thro

ugh

volc

anoe

s.

•O

ther

wis

e, c

erta

in e

lem

ents

mig

ht g

et lo

cked

into

sed

imen

t la

yers

–e.

g. e

arly

sea

life

.•

May

be p

lane

ts b

eing

for

med

no

w, w

ith le

ss s

uper

nova

e,

wou

ld n

ot h

ave

enou

gh

radi

oact

ivity

to s

uppo

rt

co

ntin

enta

l dri

fts

and

volc

anoe

s.

(Ide

a of

Pet

er W

ard

and

Don

ald

B

row

nlee

.)ht

tp://

ww

w.p

ahal

a-ha

wai

i.com

/j-p

age/

imag

e/ac

tivev

olca

noe.

jpg

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Ear

th’s

Atm

osph

ere

•E

arth

’s a

tmos

pher

e is

a

mix

ture

of

gase

s–

Nit

roge

n (N

2) 7

7%

–O

xyge

n (O

2) 2

1%

–A

rgon

Gas

(A

r) 1

%

–W

ater

Vap

or (

H2O

) 1%

–C

arbo

n D

ioxi

de (

CO

2)

0.03

3%

–T

race

gas

es (

Hel

ium

, Neo

n,

Ozo

ne, M

etha

ne, e

tc.)

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Lay

ers

of th

e A

tmos

pher

e

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Rol

es o

f th

e G

ases

•N

itrog

en is

rel

ativ

ely

iner

t(ch

emic

ally

in

activ

e)•

Oxy

gen

is u

sed

by a

nim

als

to o

xidi

ze(c

hem

ical

ly b

urn)

foo

d fo

r en

ergy

pr

oduc

tion

•W

ater

vap

or a

nd c

arbo

n di

oxid

e ar

e gr

eenh

ouse

gas

es–

Act

as

an in

sula

ting

blan

ket

–E

arth

is 3

5 K

war

mer

than

it w

ould

be

othe

rwis

e

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Lay

ers

of th

e A

tmos

pher

e

•T

ropo

sphe

re -

low

est l

ayer

, 0-1

1 km

–85

% o

f th

e ai

r–

Wea

ther

occ

urs

here

–T

empe

ratu

re d

rops

with

alti

tude

•St

rato

sphe

re -

11-5

0 km

–T

empe

ratu

re g

oes

up w

ith a

ltitu

de–

Ozo

ne la

yer

at th

e to

p

•M

esos

pher

e -

50-8

0 km

–T

empe

ratu

re a

gain

dro

ps w

ith a

ltitu

de

•Io

nosp

here

-80

+ k

m–

Tem

pera

ture

clim

bs, u

p to

100

0 K

at 2

00 k

m

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Ozo

ne L

ayer

•O

zone

is O

3

–T

hree

oxy

gen

atom

s bo

und

toge

ther

–C

reat

ed b

y su

nlig

ht

•A

bsor

bs s

olar

ultr

avio

let l

ight

–Pr

otec

ts li

fe o

n th

e su

rfac

e fr

om h

arm

ful U

V r

ays

•V

ery

low

den

sity

–If

at t

he s

ame

dens

ity a

s ne

ar th

e su

rfac

e on

ly a

few

m

m th

ick

•H

uman

-mad

e ch

emic

als

depl

ete

the

ozon

e la

yer

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Ori

gins

of

Our

Atm

osph

ere

•T

his

is th

e E

arth

’s 3

rdat

mos

pher

e

•Fi

rst w

as f

rom

for

mat

ion

–H

ydro

gen

and

heliu

m

–E

scap

ed to

spa

ce

•Se

cond

was

fro

m v

olca

noes

–C

arbo

n di

oxid

e an

d w

ater

, som

e ni

trog

en

–10

0 tim

es th

icke

r th

an o

ur a

tmos

pher

e to

day!

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Wha

t Hap

pene

d to

the

CO

2?

•W

ater

–

Prec

ipita

ted

out o

f th

e ai

r, in

to th

e oc

eans

–C

O2

diss

olve

d in

to th

e oc

eans

•L

ife

–C

onve

rted

CO

2in

the

wat

er in

to s

hells

–N

ow tr

appe

d in

sea

floo

r se

dim

ents

–Ph

otos

ynth

etic

org

anis

ms

conv

erte

d C

O2

into

O

2

•W

hat r

emai

ned

was

N2,

O2,

and

H2O

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Pre

ssur

ized

Col

lisio

ns w

ith th

e w

alls

of

the

box

tran

sfer

m

omen

tum

(ch

ange

vel

ocity

) th

at im

plie

s a

chan

ge

in a

ccel

erat

ion,

whi

ch m

eans

a f

orce

. T

hat f

orce

can

be

inte

rpre

ted

as p

ress

ure.

For

an

idea

l gas

: NkT

PV

=

Vm

NV

M/

/ :

note

==

ρ

mkT

P/

:

soρ

=

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Ear

th’s

Atm

osph

ere

•T

hink

abo

ut th

e co

lum

n of

air

abo

ve y

ou.

•C

onsi

der

a sl

ab in

that

col

umn

with

a c

onst

ant

tem

pera

ture

(is

othe

rmal

) Adh

dVdM

ρρ

==

dhA

dhg

gdM

Fw

ρ−

=−

=

Mas

s of

sla

b:

Forc

e on

sla

b:

A d

ownw

ard

forc

e, b

ut it

doe

sn’t

fal

l? W

hy?

T

he a

tmos

pher

e ha

s m

ass,

so

why

isn’

t it a

ll po

oled

aro

und

our

feet

?

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

The

Pre

ssur

e is

on

•T

here

is a

dif

fere

nce

in p

ress

ure.

–O

n bo

ttom

P(h

) an

d on

top

P(h

+dh

)

•If

the

atm

osph

ere

is in

hyd

rost

atic

equ

ilibr

ium

the

dow

nwar

d fo

rce

of g

ravi

ty is

cou

nter

ed b

y th

e up

war

d fo

rce

of p

ress

ure.

dh

h

Ah

Pdh

hP

AP

Fp

)](

)(

[−

+=

×∆

=

dhdhd

mkTA

ρ=

dhdhdP

A=

Mar

4, 2

005

Ast

rono

my

210

Spri

ng 2

005

Den

sity

Den

tist

•If

we

are

in h

ydro

stat

ic e

quili

briu

m th

en–

F w=

F p

dhdhd

AkT

Adh

gρ

ρ=

−

kTdhm

gd

−=

ρρA

tmos

pher

ic

dens

ity is

ex

pone

ntia

lly

decr

easi

ng w

ith

heig

ht!