A research team led by McGill University found the first direct evidence that during Snowball Earth, when the oceans were cut off from life-giving oxygen; glacial meltwater provided a crucially important lifeline to eukaryotes, answering a question puzzling scientists for years.
Researchers studied iron-rich rocks left behind by glacial deposits in Australia, Namibia, and California in a new study published in the National Academy of Sciences ‘ Proceedings to get a window into the environmental conditions during the ice age.
They hiked to rock outcrops using geological charts and local clues, following difficult routes to track the rock formations.
Through closely examining the natural chemistry of the iron formations in these rocks, the researchers were able to estimate the amount of oxygen in the oceans around 700 million years ago and better understand the effects it would have had on all oxygen-dependent marine life, including the earliest wild animals such as simple sponges.
Maxwell Lechte, a postdoctoral researcher at the Department of Earth and Planetary Sciences under Galen Halverson’s supervision at McGill University, says that, “The evidence suggests that although much of the oceans during the deep freeze would have been uninhabitable due to a lack of oxygen, in areas where the grounded ice sheet begins to float there was a critical supply of oxygenated melt water.”
Maxwell Lechte added that: “This trend can be explained by what we call a ‘glacial oxygen pump’; air bubbles trapped in the glacial ice are released into the water as it melts, enriching it with oxygen,”
The Earth actually experienced the most extreme ice age of its existence around 700 million years ago, threatening the survival of much of the inhabitants of the earth.
Previous research has suggested that oxygen-dependent life may have been confined to puddles of melt water on the ice surface, but this study provides new evidence of oxygenated marine environments.
“The fact that the global freeze occurred before the evolution of complex animals suggests a link between Snowball Earth and animal evolution. These harsh conditions could have stimulated their diversification into more complex forms,” Says Lechte, who is the lead author of the study as well.
Lechte points out that while the findings concentrate on oxygen availability, primitive eukaryotes would also need food to survive the harsh ice age conditions.
Future research is needed to examine how a food system could have been maintained by these conditions. Modern ice environments that today contain complex ecosystems could be a starting point.
Galen Halverson, Professor, said, “This study actually solves two mysteries about the Snowball Earth at once. It not only provides explanation for how early animals may have survived global glaciation, but also eloquently explains the return of iron deposits in the geological record after an absence of over a billion years,”.


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