Oxidants on Small Icy Bodies and Snowball Earth

Oxidants on Small Icy Bodies and Snowball Earth Yuk L. Yung (Caltech) Mao-Chang Liang (Academia Sinica)

Initiation of Snowball o Paleoclimate n n n Dim Sun Greenhouse by CH 4 (Kasting et al. ) Loss of CH 4: Oxidized by O 2 produced by oxygensynthetic bacteria ice Runaway ice-house albedo (reflectance) Hoffman, 2000

Atmospheric Photochemistry during Snowball?

Atmosphere of Snowball o o Oxygen poor Cold n n n o 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 CO 2 outgassing rate

Photochemical Calculation o One-dimensional calculation n n o o Continuity of mass ni/ t + i/ z = Pi Li Close to present-day vertical mixing profile Temperature profiles n n n 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 H 2 O 2

Principal Results O 3 O 2 CO 2 H 2 O CO

Schematic Diagram h (<200 nm) H 2 O H O 2 H 2 O 2 h (<350 nm) H 2 O 2 OH H 2 O 2 1 km diffusion H 2 O 2 ice H 2 O 2

Result Summary o o High ratio of H 2 O 2 and H 2 O ~1019 mole of H 2 O 2 could be deposited n o Decomposition of H 2 O 2 n o ~0. 1 bar of O 2 Release O 2 into the atmosphere Global oxidation on the planetary surface

Evidence of the Rise of Oxygen/Oxidants o Farquhar et al. (2000) n o Karhu, J. A. & Holland (1996) n o Mass-independent of sulfur isotopes 13 C anomaly Kirschvink et al. (2000) n Large deposition of Mn. O 2

SO 2 + h → SO + O Farquhar et al. , (2000)

Karhu & Holland, 1996

Kirschvink et al. , 2000

Impact on the Evolution of Life?

Biological Evolution Associated with Snowball o Paleoproterozic (~2. 4 Ga) n n o global oxidation event first clear fossil of eukaryotic cell (Han & Runegar, 1992) Neoproterozic (~0. 7 Ga) n n multi-cellular life Cambrian explosion

Ages in Millions of Years Cenozoic Mesozoic Paleozoic Cambrian Explosion Snowball Earth (two? ) (Precambrian) 1000 Proterozoic 2000 Oldest Eukaryote Body Fossil Introduction of Oxygen Snowball Earth (Paleoproterozoic) 3000 Archaean 3500 Oldest Stromatolite and Prokaryote Body Fossil Courtesy of Hyman Hartman

Role of H 2 O 2 Touati, 2000