Snowballing Into a New Age: How the Meltwater Pump May Have Contributed to Evolution

Image courtesy of Ellie Gabriel.

How was earth able to sustain life during a major ice age known as Snowball Earth? During that period, the planet was covered with ice sheets for millions of years. This phenomenon resulted in ocean anoxia, a phenomenon characterized by a lack of oxygen and an increase in carbon dioxide. Oceanic anoxic events threaten the survival of organisms that depend on oxygen to make energy in cellular respiration.

Yale researchers Dan Asael and Noah J. Planavsky, with a cohort of other scientists, discovered that oases beneath ice sheets may have played a role in the preservation of life during the ice age. The scientists discovered a pattern of iron formation deposits in Sturtian glaciation, the first and longest Cryogenian ice age. This is significant because iron formations indicate that there was oxygen present in glaciomarine habitats throughout that ice age, meaning it was possible that aerobic eukaryotes lived in these environments. In this study, thin sections of iron formations were polished and analyzed using light microscopy and scanning electron microscopy. This petrographic analysis of rocks allowed researchers to study the chemical compositions of the minerals to monitor the evolution of chemical weathering. The study concluded the existence of a glacial oxygen pump, which transferred atmospheric oxygen from oxic subglacial meltwater to anoxic oceans throughout the Sturtian glaciation. This allows us to understand how organisms were able to survive in such harsh climates. It also sheds light on the importance of the meltwater oxygen pump in how we understand the evolution of life.