A team of researchers at McGill University has revealed the mystery of how early animals survived the most severe ice age around 700 million years ago that had threatened the survival of life on Earth. The scientists claim to have found the first direct evidence that indicates glacial melt-water gave an important lifeline to the eukaryotes during Snowball Earth by creating oxygen pockets in the oceans.

Supply of oxygenated melt-water

"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," said Maxwell Lechte, a postdoctoral researcher in the Department of Earth and Planetary Sciences.

This trend can be explained by what is called a 'glacial oxygen pump'; whereby air bubbles trapped in the glacial ice are released into the water due to melting, enriching it with oxygen, explained Lechte, whose findings have been published in the Proceedings of the National Academy of Sciences of the United States of America.

During the study, the researchers examined the iron-rich formations, which were left by the glacial deposits in Namibia, Australia and California to understand the ecological conditions of the ice age. These rocks helped the scientists to assess the amount of oxygen present in the oceans and the impact they had created on marine life.

Ice age
Layers of glacial deposits, Death Valley (California) Maxwell Lechte

Snowball Earth and animal evolution

In contrast to this study, an earlier report had claimed that oxygen-dependent animals were possibly restricted to melt-water puddles on the surface of the ice. "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," said Lechte, who is the lead author of the study.

Apart from oxygen, Lechte pointed out that that the primitive eukaryotes would have required food to survive the extreme harsh conditions of the Ice Age. However, researchers said the finding requires further study to comment on how the food web was able to sustain for long during the ice age.

"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," said Professor Galen Halverson, who is part of the team.