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The ~4 billion year co-evolution of Earth

and its Biosphere

Instructor: Carl B. Pilcher

OLLI at SSU

Life in the Universe: The Science of Astrobiology

Week 3—April 21, 2016

SimonWilde,Cur/nUniv.,AustraliaandJohnValley,UniversityofWisconsin,Madison

TheJackHills,

WesternAustralia

Evidence from >4 BY-old zircons

Cavosie et al. 2005

Imaging U-Pb age

Oxygen isotopes

[Li] & Li isotopes

REEs, Ti Mineral inclusions

Slide courtesy John Valley

Cool Early Earth?

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Earth4.3BY

•  4.4 BY Protocontinental Crust •  >4.3 BY End of Hadean •  >3.5 BY Life >4.3 BY?

Sunonly~75%asbrightastoday4billionyearsago.SowhatkepttheEarthwarmenoughforliquidwater?

FaintYoungSunParadox

Greenhouse gases!"

Roughly30/mesmorepotentthancarbondioxide(CO2)asagreenhouse(heattrapping)gas

The Universal"Tree of Life"(adapted from Pace;"Science 276, 734, 1997)"

Bacteria

Archaea

Eucarya

Twopossibleearlymetabolisms

4H2+CO2CH4+2H2Omethanogenesis

H2+S0 H2Ssulfurrespira/on

Thesetwometabolismsarerelatedbiochemically:bothinvolvebreakingbondsbetweensulfuratoms

DidEarth’searliestlifestabilizethecondi=onsforitsownexistenceby

contribu=ngmethanetotheatmosphere?

hydrogencarbondioxidemethanewater

hydrogensulfurhydrogensulfide

Methanecanalsobeproducedabiologically,sowecan’tbesure.

Earth’sHistory

CambrianExplosion

persistent

>

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History of Oxygen

Time before Present (billion yrs)!

P O2(a

tm)!

1!

0.1!

0.01!

0.001!

0.0001!

0.00001!4.5! 4! 3.5! 3! 2.5! 2! 1.5! 1! 0.5! 0!

Multi-cellular Life!

Prokaryotic Life!

First !Eukaryotic!

Life!

“Modern” O2!levels!

Cyanobacteria

Earth’sOceanComposi/onoverGeologicTime

AnbarandKnoll,Science297,1137(2002)

Fe2+

Earth’sOceanComposi/onoverGeologicTime

AnbarandKnoll,Science297,1137(2002)

Fe2+

Sulfur-bearingrocks

SulfateSO4

2-SulfidesH2S,HS-

Oxida/veweathering

Bacterialreduc/on

“Weathering”(erosionandchemicalaltera/on)ofsulfur-bearingrocksunderanoxygen-richatmosphere

Productsflowintooceans

Sulfate-reducingbacteria!

Earth’sHistory

CambrianExplosion

persistent

>

“Dridingcon/nents”~800millionyearsago

Pangaea(~200millionyearsago)

Earth’sCrust

Earth’sInteriorStructure

PlateTectonics

Earth’sPlateBoundaries

TheCascades

Carbonate-SilicateCycle

Organismsformingcarbonateshells,par/cularlypro/sts(single-celleukaryotes),playanessen/alroleincarbonaterockforma/on

Carbonate-SilicateCycle

M Vogt, Science 2015;350:1466-1468

CarbonDioxideCycle(shortertermthermostat)

Earth’sOceanComposi/onoverGeologicTime

AnbarandKnoll,Science297,1137(2002)

Fe2+

SnowballEarth

SnowballEarthsarethoughttohaveoccurred2.2-2.4BYago,justaderthebuild-upofoxygeninEarth’satmosphere,and580-750millionyearsago,justbeforetheCambrianExplosionwhenlarge,diverse,morecomplexanimalsappearabruptlyinthefossilrecord.

MassEx/nc/ons

Cretaceous-Ter/ary(K/T)Ex/nc/onEvent

CausesofMassEx/nc/ons

•  Theother4majormassex/nc/ons,aswellassmallerex/nc/onevents,appearnottobeassociatedwithimpacts;thecausesappeartobegeological/biological.–  Theex/nc/onsweregradualorepisodic,occurringoverhundredsofthousandstomillionsofyears.

–  Therearefewifanyimpactscratersoftherightage.–  Therearecrediblegeological/biologicalexplana/ons.

ThePermian-Triassic(P/T)Ex/nc/on•  The“motherofallex/nc/ons”

–  ≤96%ofalloceanspeciesand~70%ofalllandspeciesdiedoff•  TheSiberianfloodbasalterup/onscoincidedwiththeex/nc/ons.–  Anarearoughlythesizeofthe48con/guousstateswascoveredwithlavatoanaveragedepthofaboutamileoverapproximatelyamillionyears

– Muchoftheerup/onoccurredthroughtheworld’slargestcoalbasin,probablyconver/ngmuchofthecoaltocarbondioxideandmethane,bothimportantgreenhousegases.

–  Increasedatmospherictemperaturewouldleadtoincreasedrainfallandcon/nentalweathering,producingmoresulfaterunoffintotheoceans,returningtheoceanstemporarilytothesulfidiccondi/onsofthemid-Proterozoic.

D.H.Erwin,Ex=nc=on:HowLifeonEarthNearlyEnded250MillionYearsAgo,PrincetonUniv.Press,2006

Conclusions•  Earthhasbeenhabitableforatleast3.5-4billionyearsandperhapslonger,almostsinceitsforma/on4.54billionyearsago.

•  AninterplayofgeologicalandbiologicalprocesseshasbeenresponsibleformaintainingEarth’shabitabilityoversuchalonginterval,despiteasubstan/alchangeinthebrightnessofthesun.

•  Thecourseofbiologicalevolu/onhasbeenaffectedbytheinterplayofgeologicalandbiologicalforces.–  Ifwecould“replaythetapeoflife”,itisveryunlikelythatwewouldreproducethesamehistoryoflifeonEarth.

S.J.Gould,WonderfulLife:TheBurgessShaleandtheNatureofHistory,Norton,1989

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Questions?

QUESTIONS?