WhyistheEarthhabitable?

15°C

-55°C

460°C

Anthropicprinciple

“We’reherebecauseweare…”

TheGaiaTheory

JamesLovelockLynnMargulis

“Lifeispartofaself-regula@ngsystem,manipula@ngthephysicalandchemicalenvironmenttomaintaintheplanetasasuitablehomeforlifeitself.”

“GaiacannotarisefromDarwinianevolu@onoflife—theplanetasawholeisnotaunitofselec@on.”

RichardDawkins

SnowballEarth

Jaffresetal.,2007

Carbon

Berner,1999,GSAToday

WeatheringandCO2Carbonateweathering:Rockatmos.Riversoceansatmos.

CaCO3+CO2+H2O=>Ca2++2HCO3-=>CaCO3+CO2+H2O

Silicateweathering:Rockatmos.Oceansatmos.

(Ca,Mg)SiO3+2CO2+2H2O=>(Ca,Mg)CO3+SiO2+CO2+2H2OSilicateweatheringburiescarbonascalciteordolomite

Do we need a feedback cycle?

BernerandCaldiera,1997 CO2 outgassing

Greenhouse warming

Increased chemical weathering

Increased CO2 burial

Cooling

Temperature feedback model

e.g. Walker et al., 1981

ClimateacrossEarthhistory

Hessler,2011,NatureEduca@on

Past CO2

Zachosetal.,2008

Tectonics

Importance of silicate weathering

CO2 outgassing

Greenhouse warming

Increased chemical weathering

Increased CO2 burial

Cooling Uplift

Increased physical erosion

Increased weathering and CO2 burial

Cooling

Temperature feedback model Mountain uplift model

e.g. Walker et al., 1981 e.g. Raymo et al., 1988, Raymo & Ruddiman, 1992

BeachyHead,EastSussex

δ13C

OceanicAnoxicEvents

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-15 -10 -5 0 5 10

Time(M

a)

Norm.δ7Li

Post-Marinoan

OAE2

PETM

Hirnan@an

Timingofweatheringcontroloverclimate

50ka

250ka(4xincrease)280ka(1.5–2xincrease)

509ka(2xdecrease)

Colbou

rneetal.,2015

Sund

quist,1991

Oxygen

Why assume steady state?

BernerandCaldiera,1997

Temperaturefeedbackmodel

e.g.Walkeretal.,1981

Cenozoicseawaterδ7Li

Misra&Froelich,2012,Science