Snowbal l Earth Roopa Kamesh Matt Beversdorf Kathy Groome

Theory of Snowball Earth Continents and oceans were covered in ice approximately 600 million years ago. Earth was in a deep freeze, chemical cycles were halted; carbon dioxide accumulated in the atmosphere causing an extreme greenhouse effect. Believed to have triggered the explosion of life forms seen in Cambrian fossils

Snowball Earth occurred during the Neoproterozoic

Research Question Is there a correlation between the existing isotope data and unusual deposits during the Neoproterozoic ( Ma) ?

Existing Evidence Proterozoic Biostratigraphy: Persistence and the Explosion of Life Glacial Deposits and Carbonate Caps Isotope Analysis

Proterozoic Biostratigraphy (Fossil Record) Shelly Fauna – mollusks, conical fossils marking the Cambrian transition Acritarchs – organic walled, probably plant origin Ediacarian fossils – oldest known multicellular animal life. Soft bodied, macroscopic invertebrates. Circumglobal Stomatolites – CaCO3 buildup of algal origin Trace fossils – traces and burrows

Hoffman and Shrag (1998)

Geologic Sequence Cap Carbonates are found on top of glacial deposits in the rock layers. Mulden Clastics Elandshoek Slope Elandshoek Platform Maieberg Cap Carbonate Ghaub Glacial Deposits Ombaatijie Platform Gruis Ramp Rasthof Cap carbonate Chuos Glacial Deposits Ombombo Ramp (approx 760 Ma) Namibia (Hoffman et al. 1998)

Hoffman and Schrag pointing to cap carbonate above glacial dropstones.

Stable Isotope Analysis OXYGEN Heavy Oxygen-18 is incorporated into minerals. More Oxygen 18 during low temperatures. STRONTIUM Increased Sr86/87 ratio due to increased weathering during glaciation. CARBON 12/CARBON 13 Plants use the lighter isotope Carbon 12 in photosynthesis. The lower relative abundance of Carbon 13 means the plants were worse off (dying). Evidence in “cap” carbonates Jacobson and Kaufmann, 1999 Knoll, 2000

Design/Methods Literature Search for related data Kaufman et al The Vendian Record of Sr and C isotopic Variations in Seawater: Implications for Tectonics and Paleoclimate. Earth and Planetary Science letters 120(1993) Kennedy et al Two or Four Neoproterozoic Glaciations? Geology 26 (12): Data Analysis Create Timeline depicting different stages ranging from Archaen to Phanerozoic Any significant difference in isotope data over time (ANOVA for 3 different isotopes every 20 My) Correlation between isotope data at different locations (ANOVA for 3 different isotopes) Correlation between different isotope data (Spearman rank analysis)

Results

Data grouped by 20 My time periods. (A= My, I= My) Oxygen (O18) Carbon 13 Strontium (Sr86/Sr87) IsotopeP-valueAge groups included Carbon A-I Oxygen A-F Strontium 87/ A-I Isotope Data over Time

Isotope Data from Different Locations

Strontium (Sr86/Sr87) Oxygen (O18) Carbon 13 IsotopeP-value Carbon Oxygen Strontium *.0018* C, O and Sr for 5 locations *Low P-value means that they are significantly different

Correlation Between Isotope Data? *Low P-value means that we reject the null hypothesis that there is not a relationship between the variables (independent)

Summary of the Results ANOVA * C, Sr, and O were significantly different over time Indicates one or more climatic changes in conditions from the Archaen to the Phanerozoic. (Does not tell us when or how extreme) * O and Sr were significantly different between locations Tells us that the numbers are different between sites - measurement error or other factor? (Does not tell us if locations show same trend) * C was not significantly different between locations Carbon data was similar for all sites SPEARMAN * Both C & Sr and C & O are not related * O & Sr are related (inverse correlation)

Walter et al., 2000 How does it all fit together? (after 6 hours of stress)

Conclusion We conclude that it is reasonable that a global glaciation occurred around 600 My ago. This is supported by isotope analysis, which showed that isotopes changed over time over a large area. The isotopes also correspond with glacial deposits and biostratigraphic data What do you think?