EAGER: An Oasis for Surface Life on the Ocean of Snowball Earth

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There is now compelling evidence for times in the distant past when the Earth was in a deep freeze, with ice sheets hundreds of meters thick covering the world's oceans. These "snowball earth" episodes lasted for millions of years during the Cryogenian period, between 720 and 630 million years ago. Somehow, despite thick ice cover and surface temperatures 30 Celsius below zero, life survived on snowball earth. Among the survivors were multicellular species of algae which rely on photosynthesis and must have lived at the surface or below ice thin enough to transmit sunlight. Given the harsh conditions it is natural to look for refugia, special places which remained unusually hospitable due to favorable local conditions.Research under this award considers the possibility that the refugia of snowball earth were bays at the far ends of protected tropical seas similar to the Red Sea today. Previous work by the Principal Investigators (PIs) shows that such a sea could keep out the "sea glaciers" that covered the open oceans. But the sea would also need to be in an unusually warm region to prevent thick ice from growing locally. The PIs hypothesize that such warmer conditions could occur if the sea were surrounded by bare land with a relatively dark (or low albedo) surface to promote solar absorption. Warmer local climate could also occur due to favorable configurations of mountain ranges around the sea.Work performed here tests the protected sea refugia hypothesis using climate model simulations configured to represent conditions on snowball earth. The continental configuration is adjusted to include a protected sea, and the albedo of the surrounding land is varied to determine if a darker land surface can produce a regional climate warm enough to allow open water. Other aspects of the configuration are also varied, such as the size of the sea and the presence of mountain ranges around it.The work has broader impacts due to the importance of the problem for understanding life on earth, and it also has implications for efforts to find evidence of life on other planets. Results of the research are presented to the public through several outreach activities, and the PIs use the snowball earth problem as a way to motivate K-12 students to learn more about earth science during class visits to the University of Washington campus.This project is jointly funded by the Climate and Large-scale Dynamics Program (PD 06-5740) and the Arctic Natural Sciences Program (PD 16-595).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.