1. Department of Oceanography, Texas A&M University, College Station, Texas 77843-3146, USA
2. Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada

Correspondence to: Correspondence and requests for materials should be addressed to W.T.H. (e-mail: hyde@rossby.tamu.edu).

Abstract

Ice sheets may have reached the Equator in the late Proterozoic era (600–800 Myr ago), according to geological and palaeomagnetic studies, possibly resulting in a 'snowball Earth'. But this period was a critical time in the evolution of multicellular animals, posing the question of how early life survived under such environmental stress. Here we present computer simulations of this unusual climate stage with a coupled climate/ice-sheet model. To simulate a snowball Earth, we use only a reduction in the solar constant compared to present-day conditions and we keep atmospheric CO₂ concentrations near present levels. We find rapid transitions into and out of full glaciation that are consistent with the geological evidence. When we combine these results with a general circulation model, some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals.

1. Department of Oceanography, Texas A&M University, College Station, Texas 77843-3146, USA
2. Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada

Correspondence to: Correspondence and requests for materials should be addressed to W.T.H. (e-mail: hyde@rossby.tamu.edu).