How life survived Snowball Earth, the planet's most severe ice age

In this image obtained from NASA, the space agency's DC-8 flies over the Pine Island Glacier Ice Shelf on October 14, 2011.

(CNN)Around 700 million years ago, the world is thought to have experienced its most severe ice age -- a period evocatively described by scientists as Snowball Earth.

It threatened the survival of much of the planet's primitive living things, like oxygen-dependent marine life -- including the earliest animals, such as simple sponges.
But new geological evidence uncovered by scientists at McGill University in Montreal has found that glacial meltwater provided a crucial lifeline at the time to microscopic organisms known as eukaryotes.
"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 meltwater," said McGill University sedimentologist Maxwell Lechte in a press statement.
    Previously, scientists thought that oxygen-dependent life may have been restricted to meltwater puddles on the surface of the ice, but the new study published Monday in the journal Proceedings of the National Academy of Sciences provides evidence of "oxygen oases" below the ice where the glacier meets the sea. These would have allowed primitive life forms to wait out the ice age.
    Lechte, who is also a postdoctoral researcher in the Department of Earth and Planetary Sciences at McGill University, said that air bubbles trapped in the glacial ice were released into the water as it melts, enriching it with oxygen, a process he described as a "glacial oxygen pump."