New Evidence Hints at Global Glaciation 716.5 Million Years Ago

Cambridge, Mass. March 4, 2010 - Geologists have found evidence that sea ice extended to the equator 716.5 million years ago, bringing new precision to a “snowball Earth” event long suspected to have taken place around that time. Led by scientists at Harvard University, the team reports on its work this week in the journal Science. The new findings – based on an analysis of ancient tropical rocks that are now found in remote northwestern Canada – bolster the theory that our planet has, at times in the past, been ice-covered at all latitudes. “This is the first time that the Sturtian glaciation has been shown to have oc-curred at tropical latitudes, providing direct evidence that this particular glaciation was a ‘snowball Earth’ event,” says lead author Francis A. Macdonald, an assistant professor in the Department of Earth and Planetary Sciences at Harvard. “Our data also suggests that the Sturtian glaciation lasted a minimum of 5 million years. The survival of eukaryotic life throughout this period indicates sunlight and sur-face water remained available somewhere on the surface of Earth. The earliest animals arose at roughly the same time, following a major proliferation of eukaryotes. Even in a snowball Earth, Macdonald says, there would be temperature gradi-ents on Earth and it is likely that ice would be dynamic: flowing, thinning, and forming local patches of open water, providing refuge for life. “The fossil record suggests that all of the major eukaryotic groups, with the pos-sible exception of animals, existed before the Sturtian glaciation,” Macdonald says. “The questions that arise from this are: If a snowball Earth existed, how did these eukaryotes survive?