THE NEXT FOUR BILLION YEARS:

MAKING EARTH HABITABLE (FOR HUMANS)

Steve KeslerGeologicalSciences

EARTH – Special Features of Earth.

CONTINENTS

OCEAN

ATMOSPHERE

S Kesler, UMich

EARTH HISTORY –Evolution of continents, ocean, atmosphere. Evidence for life.

CONTINENTS

OCEAN

ATMOSPHERE

S Kesler, UMich

EARTH HISTORY – Geologic Time Scale

Had

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S Kesler, UMich

Mantle

Continental and Ocean Crust

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Homogeneous Early Earth

HADEAN HISTORY

Core

Layered Earth

1 - Formation of the Core and Mantle - T=+30 M yrs

XS Kesler, UMich

http://www.meteorites21.com

Typical starting materialCHONDRITIC METEORITE

HADEAN HISTORY

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CHONDRULES

1 - Formation of the Core and Mantle - T=+30 M yrs

S Kesler, UMich

http://www.psrd.hawaii.edu/

COREFe

MANTLEMg-Si-O

HADEAN HISTORY1 - Formation of the Core and Mantle - T=+30 M yrs

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Core

Mantle

Continental and Ocean Crust

Heated byAccretion

Radioactivity

Melting

Iron sinks

~1000ºC

XS Kesler, UMich

HADEAN HISTORY

http://www.daviddarling.info/encyclopedia/P/protoplandisk.html

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2 – Bombardment and Origin of Moon – T=+50 M yrs

SUN

PLANET

PLANETISSIMALS AND OTHER DEBRIS

S Kesler, UMich

HADEAN HISTORY

http://starchild.gsfc.nasa.gov

LARGE IMPACTORORIGIN OF MOON

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MODEL OF IMPACT SEQUENCE

http://www.swri.edu/3pubs/ttoday/spring99/moon.htm

2 – Bombardment and Origin of Moon – T=+50 M yrs

S Kesler, UMich

H2O, CO2, H2

HADEAN HISTORY

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?????

~0.1% H2Oand other

gases

3 – Formation of Early AtmosphereWater and gases

driven out bymelting

S Kesler, UMich

H2O, CO2, H2

HADEAN HISTORY

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???

4 – Formation of the Ocean

EARTHCOOLED

THE GREAT RAIN

THE GREAT RAIN

OCEANS Kesler, UMich

H2O, CO2, H2

HADEAN HISTORY

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4 – Formation of the Ocean

EARTHCOOLED

THE GREAT RAIN

THE GREAT RAIN

1 – VOLUME OF THE OCEAN2 – AGE OF THE OCEAN

???

OCEANS Kesler, UMich

http://www.geology.wisc.edu/zircon/

Had

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5 – Formation of Early Crust - Jack Hills, Australia3.6 Billion Year Old

Conglomerate(Stream Gravel)

4.3 Billion Years Old

JOHN VALLEY

S Kesler, UMich

http://www.geology.wisc.edu/zircon/

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3.6 Billion Year OldConglomerate

(Stream Gravel)

Zircon Grain(Zr2SiO4)

HADEAN HISTORY 5 – Formation of Early Crust - Jack Hills, Australia

4.3 Billion Years Old 100 μm S Kesler, UMich

http://www.geology.wisc.edu/zircon/

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3.6 Billion Year OldConglomerate

(Stream Gravel)

Zircon Grain(Zr2SiO4)

HADEAN HISTORY 5 – Formation of Early Crust - Jack Hills, Australia

4.3 Billion Years Old 100 μm

4.3 Billion Years

S Kesler, UMich

http://earthweb.ess.washington.edu/~jelte/

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~3.8 Billion Years Old

HADEAN HISTORY 5 – Formation of Early Crust – Isua, Greenland

S Kesler, UMich

http://www.denison.edu/geology/greene/

LAVA FLOW

Pillow-like shapeformed in water.

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~3.8 Billion Years Old

HADEAN HISTORY 5 – Formation of Early Crust – Isua, Greenland

S Kesler, UMich

MANTLEMg-Si-O

MID-OCEANRIDGE

OCEANCRUST

Mg-Fe-Si-O

CONTINENTAL CRUSTNa-K-Ca-Al-Si-O

SUBDUCTIONZONE

PLATE TECTONICS AND RELATED PROCESSESOcean Crust at Mid-Ocean RidgesContinental Crust at Subduction Zones

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1 - Growth of CrustARCHEAN AND PROTEROZOIC HISTORY

S Kesler, UMich

ZONE OFMELTING

AGE (BILLION YEARS)3.8 3.4 3.0 2.6 2.2 1.8 1.4 1.0 0.6 0.2

15

10

5 FREQ

UEN

CY

Condie et al., EPSL, 1998

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ISUA

ARCHEAN AND PROTEROZOIC HISTORY2 - Supercontinent Cycles Build Continental Crust

S Kesler, UMich

H2O, CO2, H2

PROTEROZOIC HISTORY

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1 – Formation of Oxygen-Bearing Atmosphere

NO O2!!

S Kesler, UMich

H2O, CO2, H2

PROTEROZOIC HISTORY

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1 - Formation of Oxygen-Bearing Atmosphere

MOSTLIKELYSOURCE

Photosynthesis

6CO2 + 12H2O+ light energy →C6H12O6 + 6O2 + 6H2O

Cyanobacteria

NO O2!!

S Kesler, UMich

OXYGEN-RICHATMOSPHERE

DominatedBy Life

REDUCINGATMOSPHERE

DominatedBy Degassing

FORMATIONOF OZONE

Canfield, Ann Rev., 2005

PROTEROZOIC HISTORY1 - Formation of Oxygen-Bearing Atmosphere

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2020.2

0.02

OXYGEN CONTENT (%)S Kesler, UMich

OXYGEN-RICHATMOSPHERE

DominatedBy Life

REDUCINGATMOSPHERE

DominatedBy Degassing

FORMATIONOF OZONE

Canfield, Ann Rev., 2005

PROTEROZOIC HISTORY1 - Formation of Oxygen-Bearing Atmosphere

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2020.2

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OXYGEN CONTENT (%)

OLDEST FOSSILS

OLDEST CYANOBACTERIA FOSSILS

STROMATOLITE

S Kesler, UMich

SNOWBALLEARTH

http://www.arctic.uoguelph.ca

THREE FINAL ISSUES1 - Regulating Surface Temperatures

S Kesler, UMich

http://www.environment.sa.gov.au

The Greenhouse EffectH2O, CO2, CH4

THREE FINAL ISSUES1 - Regulating Surface Temperatures

S Kesler, UMich

THREE FINAL ISSUES1 - Regulating Surface Temperatures

S Kesler, UMich

http://solarsystem.nasa.gov/

VENUSEARTH

MARS

12°-24ºC 477°C

-53°CFailure on Other Rocky Planets

Average Surface Temperatures

RUNAWAYGREENHOUSE

ICEBOX

THREE FINAL ISSUES1 - Regulating Surface Temperatures

REGULATEDGREENHOUSE

S Kesler, UMich

http://www.gly.fsu.edu/~salters/GLY1000/

0 MILLIONS OF YEARS 180

http://web.mit.edu/mit-whoi/

THREE FINAL ISSUES2 - Formation of Mineral Deposits

Human life requiresmineral deposits

Formation of ocean crustat mid-ocean ridges

Seawater heatedat mid-ocean ridge

DEEP OCEAN FLOOR (5 km)

S Kesler, UMich

350ºCwater

containingmetal

sulfides

0.5

met

er

http://www.dfo-mpo.gc.ca/

Cross Section of Chimney

THREE FINAL ISSUES2 - Formation of Mineral Deposits DEEP OCEAN FLOOR (5 km)

S Kesler, UMich

http://www.dfo-mpo.gc.ca/

THREE FINAL ISSUES3 - Geologic Setting for Early Life

DEEP OCEAN FLOOR (5 km)Protected environment

TUBE WORMS

S Kesler, UMich

THREE FINAL ISSUES3 - Geologic Setting for Early Life

Russell et al., 2005, Economic Geology

DEEP OCEAN FLOORPROTECTED ENVIRONMENT

S Kesler, UMich

CONTINENTS

OCEAN

ATMOSPHERE

EARTH IS THE BEST PLACE TO START

S Kesler, UMich