Media release

From: Springer Nature

Environment: Life found a way to survive on ‘Slushball Earth’ 

Habitable marine environments for the earliest forms of complex life may have been more extensive than previously thought during the Marinoan Ice Age, between 654–635 million years ago, according to a paper published in Nature Communications. The findings suggest that habitable open-ocean conditions may have persisted even up to the mid-latitudes during the proposed ‘Snowball Earth’ event, implying it was more of a ‘Slushball Earth’ event, allowing organisms to survive during periods of near global freezing.

How complex life may have survived through the Marinoan Snowball Earth glaciation has been a topic of much debate. Ocean refuges were thought to have existed for marine organisms to survive during the Snowball Earth event of the Marinoan glaciation. However, the environmental conditions that allowed these organisms to survive remain poorly understood.

Huyue Song and colleagues analysed the geochemical composition of fossil-rich sediments within the late Cryogenian Nantuo Formation, south China, dating between 654–635 million years old. They found fossils resembling seafloor-dwelling photosynthesising algae. Additionally, the iron chemistry indicated that the deep water was poorly oxygenated, but aerobic nitrogen recycling likely occurred in oxygenated surface water. During the final Snowball Earth glaciation, these sediments were found to be deposited between 30–40 degrees north, substantially further north than any unfrozen ocean may have been expected.

The authors suggest that these mid-latitude open-ocean sites provided refuges for complex organisms to survive through periods of near global freezing, allowing life to persist until conditions became more amenable.