Goals for this section1. EXPLAIN the feedback mechanism believed to have

maintained Earth's average temperature within the range of liquid water over 100s of millions of years, as the Sun got brighter.

2. Based on albedo, solar radiation, and atmospheric gases, CONSTRUCT logical chains of events that would result in major glaciations or warm periods on Earth.

3. IDENTIFY and EXPLAIN the primary trends and climate events of the past 65 million years based on oxygen isotope data.

Long-Term Climate Evolution: Quiz 5: Nov 30-Dec 1

Final review is Dec 4: Submit Qs on Discussion Board

RELEVANCE

4.5

billi

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ears

ago

– E

arth

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ms

2.5-

2.3

billi

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ago

–

Hu

ron

ian

gla

ciat

ion

s

800-

600

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year

s ag

o –

Sn

ow

bal

l E

arth

WARMWARM

What next? More ICE

SNOWBALLEARTH

Ice in Australia, which was then at the equator

Evidence for Snowball Earth

Clicker Question: How could having all continents bundled near the equator help trigger a global glaciation?

A. The continents must have had high mountains where glaciers could form

B. Warm temperatures in the tropics would keep silicate weathering rates high

C.There would be less volcanism if all the continents were in the tropics

D.The poles could freeze more easily if they were water-coveredE. All of the above

Getting into Snowball Earth

Continents at low latitudes chem weathering CO2 colder

Ice expansion albedo runaway ice-albedo feedback SNOWBALL

Ho

ffma

n &

Sch

rag

Clicker question: What’s the most likely factor to help Earth escape from the “snowball” scenario? A. Increased burial of organic carbon (e.g. coal

deposits)B. Increased solar outputC. Lower sea levelD. Volcanic activityE. Biological production of oxygen

Escape from Snowball Earth Tectonics & volcanism CO2

Ho

ffma

n &

Sch

rag

Ice cover prevents chem weathering CO2 even more… greenhouse finally gets strong enough to melt ice ice-albedo feedback

Clicker question: Once the ice sheets starting melting, more land surface was exposed. What kind of feedback loop between ice and albedo would be triggered as the Earth came out of the Snowball scenario?

A. Positive feedback loopB. Negative feedback loopC. NeitherD. Both

300-

270

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ion

year

s ag

o –

Per

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-Car

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nif

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gla

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s

4.5

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on y

ears

ago

– E

arth

for

ms

2.5-

2.3

billi

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ears

ago

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Hu

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gla

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s

800-

600

mill

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year

s ag

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Sn

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bal

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WARMWARM

Warm again, cold again…

WA

RM

Clicker question: The Permo-Carboniferous glaciations happened when all the continents were together in the supercontinent Pangaea. What effect would the process of assembling a supercontinent have on greenhouse gas concentrations? Greenhouse gases would ______. A. IncreaseB. DecreaseC. Stay the same

CO

LD!

Decreased atmospheric CO2 as Pangaea formed

Causes of the P-C glaciations

Causes of the P-C glaciations

Formation of coal deposits

ICE

COAL DEPOSITS

Ice cover during the P-C glaciations

Clicker question: Why didn’t the Earth turn into a snowball this time?

A. As the continental ice sheets grew, sea level fell.

B. Glaciers excavated the new swamp deposits.

C. Ice cover on polar continents decreased silicate weathering.

D. Swamps output additional oxygen.

4.5

billi

on y

ears

ago

– E

arth

for

ms

2.5-

2.3

billi

on y

ears

ago

–

Hu

ron

ian

gla

ciat

ion

s

800-

600

mill

ion

year

s ag

o –

Sn

ow

bal

l E

arth

WARMWARM

Warm again, cold again, warm again…

WA

RM

300-

270

mill

ion

year

s ag

o –

Per

mo

-Car

bo

nif

ero

us

gla

ciat

ion

s

WA

RM

Pangaea was breaking apartHigher rates of seafloor spreadingIncreased CO2 from volcanoes

Causes of the post-glacial warming

4.5

billi

on y

ears

ago

– E

arth

for

ms

2.5-

2.3

billi

on y

ears

ago

–

Hu

ron

ian

gla

ciat

ion

s

800-

600

mill

ion

year

s ag

o –

Sn

ow

bal

l E

arth

WARMWARM

Finally, the past 65 million years

WA

RM

300-

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WA

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Last

2.5

mill

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year

s –

Ple

isto

cen

e g

laci

atio

ns

XNo more dinos!

70 60 50 40 30 20 10 0 Million years ago

LOW

“T

empe

ratu

re”

HIG

H

Warming prior to 50 Ma

70 60 50 40 30 20 10 0 Million years ago

LOW

“T

empe

ratu

re”

HIG

H

Subduction of carbon-rich sediments under Asia

Warm

ing

Cooling after 50 Ma

70 60 50 40 30 20 10 0 Million years ago

LOW

“T

empe

ratu

re”

HIG

H

Collision produced mountains and increased chemical weathering

Long-term cooling

Benthic Forams: CaCO3

Estimating past temperatures

Ocean

Sediments

Deep ocean temperature

18O

For an ICE-FREE WORLD

??

H218O H2

16OH216O

Distillation of water Fractionation of oxygen isotopes

H216O (light) & H2

18O (heavy)

H216O

H216O

H216O

?

Clicker Q: How would the oxygen isotopic composition of the water in an ice sheet compare to the oxygen isotopic composition of ocean water during an ice age?

A. Ice would be heavier than oceanB. Ice would be lighter than oceanC. Ice would be the same as ocean

?

16O“lighter”

18O“heavier”

H216O

H218O H2

16OH216O

Evidence: Distillation of water Fractionation of oxygen isotopes

16O (light) & 18O (heavy)

Sea level Ice sheet size

Temperature or 18O in the ocean 18O in the shells

Foraminifera: CaCO3

CaC16O16O16OCaC16O16O18OCaC16O18O18O

lighter

heavier

[ ]18O =18O/16Osample

18O/16Ostandard

-1 * 1000

18O/16O measured in shells

Higher 18O colder water temperatures (and/or more ice)

Lower 18O warmer water temperatures (and/or less ice)

Estimates of past temperatures

Who’s driving?

Total “forcing” based on temperature estimates

Changes in solar radiation and albedo

Changes in greenhouse gases

Pleistocene Glaciations

Causes of the Pleistocene glaciations:

India-Asia collision – decreased greenhouseIce-albedo feedbacks once ice formed on Antarctica

Summary: Long-term Climate Evolution • The “faint young Sun” paradox can be resolved by higher greenhouse gas concentrations in Earth’s early atmosphere.• Each of the 4 major glacial periods in Earth’s history occurred under different circumstances with different perturbations and feedbacks (construct the logical chains of events for each):

• Huronian – rise of atmospheric oxygen, drawing down methane• Snowball Earth – continents in tropics, high weathering rates, ice-albedo feedbacks• Permo-Carboniferous – mountain building and organic carbon burial• Pleistocene – mountain building (Himalayas), then ice- albedo feedbacks

• Oxygen isotope records from the past 65 My record temperature changes that help resolve the three main climate driving forces in this period – the Sun, albedo, and greenhouse.