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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?
5
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
>
11
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
44
Questions?
QUESTIONS?
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