Oxidants on Small Icy Bodies and Snowball Earth

Yuk L. Yung (Caltech)

Mao-Chang Liang

(Academia Sinica)

Initiation of Snowball

Hoffman, 2000

Paleoclimate Dim Sun Greenhouse by CH4 (Kasting et al.) Loss of CH4: Oxidized by O2 produced by oxygen-synthet

ic bacteria

ice

albedo(reflectance)

Runaway ice-house

Atmospheric Photochemistry during Snowball?

Atmosphere of Snowball

Oxygen poor Cold

Surface temperature -40 C Low water vapor abundance Weak hydrological cycles (~1 mm/yr)

100 Myr to get rid of the Snowball, by assuming present CO2 outgassing rate

Photochemical Calculation One-dimensional calculation

Continuity of mass ni/t + i/z = Pi Li

Close to present-day vertical mixing profile Temperature profiles

Surface temperature of 210, 240, 273 K Lapse rate of 6.5 and 10 K km-1

Deposition rate of ~109 molecules cm-2 s-1 for H2O2

Principal Results

O3

H2O

H2O2

O2

H2CO

CO2

H2O2

ice

H2O2

H2O2

H2O2H2O2

H2OHO2

HO2 H2O2

OH

H2O2

H2O2 H2O2

H2O2

H2O2H2O2

1 km

diffusion

Schematic Diagram

h (<200 nm)

h (<350 nm)

Result Summary

High ratio of H2O2 and H2O

~1019 mole of H2O2 could be deposited ~0.1 bar of O2

Decomposition of H2O2

Release O2 into the atmosphere

Global oxidation on the planetary surface

Evidence of the Rise of Oxygen/Oxidants

Farquhar et al. (2000) Mass-independent of sulfur isotopes

Karhu, J. A. & Holland (1996) 13C anomaly

Kirschvink et al. (2000) Large deposition of MnO2

Farquhar et al., (2000)

SO2 + h → SO + O

Karhu & Holland, 1996Karhu & Holland, 1996

Kirschvink et al., 2000Kirschvink et al., 2000

Impact on the Evolution of Life?

Biological Evolution Associated with Snowball

Paleoproterozic (~2.4 Ga) global oxidation event first clear fossil of eukaryotic cell (Han & Runega

r, 1992) Neoproterozic (~0.7 Ga)

multi-cellular life Cambrian explosion

Ages in Millions of Years

Oldest Stromatolite and Prokaryote Body Fossil

Oldest Eukaryote Body FossilIntroduction of OxygenSnowball Earth (Paleoproterozoic)

Cambrian ExplosionSnowball Earth (two?) (Precambrian)

3500

3000

2000

1000

Archaean

Proterozoic

CenozoicMesozoic

Paleozoic

Courtesy of Hyman Hartman

Role of H2O2

Touati, 2000