Testing the Snowball Earth Hypothesis
OCCI Funded Project: 2005
Paul Hoffman (Harvard University)
Birger Schmitz (Lund University, Sweden)
Bodiselitsch et al. (2005, Science) reported concentration anomalies of iridium, a tracer of extraterrestrial material, in basal layers of cap dolomite formations that overlie glacial sediments deposited during the Sturtian (~710 Ma) and Marinoan (~635 Ma) Neoproterozoic "Snowball Earth" glaciations. They hypothesize that these Ir anomalies reflect instantaneous deposition, during deglaciation, of cosmic dust that has been stored for millions of years on the global ice cover. If correct, this hypothesis lends support to the "hard" Snowball Earth hypothesis (i.e., Earth frozen to the equator) instead of the "Slushball Earth" hypothesis which allows for the existence of open water in the tropics.
With funding from WHOI's Ocean and Climate Change Institute we are using a range of geochemical tracers (osmium isotopes, platinum group element concentrations, helium isotopes and concentrations) to detect the presence of extraterrestrial matter in Snowball Earth deposits. Our field work in Namibia in August 2005 was aimed at recovering continuous sections across the glacial-postglacial transition (see Fig. 1). Work on correlative sections from Canada (Mackenzie Mountains) China and, possibly, Brazil is planned for the coming year.