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The ~4 billion year co-evolution of Earth
and its Biosphere
Instructor: Carl B. Pilcher
OLLI at SSU/Oakmont
Life in the Universe: The Science of Astrobiology
Week 3—January 28, 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?
TheFaintYoungSunParadox
• Modelsofstellarevolu/onandobserva/onsoflargenumbersofstarsindicatethatstarsgetbrighterastheyage.
• Thesunhadonly~75%ofitscurrentluminosity(energyoutput)around4billionyearsago.
• YettherewasapparentlyliquidwateronEarthatthat/me,implyingasurfacetemperatureroughlyequaltoorgreaterthanthesurfacetemperaturetoday.
• Howcouldthishavebeenthecase?
ManyPossibleExplana/onsfortheFaintYoungSunParadox
• Moreatmosphericcarbondioxide(CO2;greenhousegas)• Moreatmosphericmethane(CH4;greenhousegas)• Moreatmosphericammonia(NH3;greenhousegas;butreadilydestroyedbyultravioletradia/on)
• Organichazeshieldingatmospherefromradia/on,enablingNH3toincrease
• Atmospherichydrogen(H2)andnitrogen(N2)togetheringreaterabundance(actlikeagreenhousegas)
• Fewerclouds,allowingEarthtoabsorbmoresunlight(effectisn’tlargeenough)
• Sunwasn’treallythatmuchfainter
Twopossibleearlymetabolisms
H2+S0 H2Ssulfurrespira/onhydrogensulfurhydrogensulfide
4H2+CO2CH4+2H2Omethanogenesishydrogencarbondioxidemethanewater
Didlifehelpstabilizethecondi2onsforitsownexistencebycontribu2ng
methanetoEarth’searlyatmosphere?!
Earth’sHistory
10
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
“Drihing”con/nentsandPlateTectonics
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
Earth’sOceanComposi/onoverGeologicTime
AnbarandKnoll,Science297,1137(2002)
Fe2+
SnowballEarth
SnowballEarthsarethoughttohaveoccurred2.2-2.4BYago,justaherthebuild-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,Ex2nc2on: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?
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