Oxygen needs to be present for iron to rust. It also needs to be present for animals and many other organisms to survive. If the iron rocks below the ancient oceans rusted, then there was also oxygen in those oceans. And if there was oxygen, then oxygen-breathing life-forms had a lifeline they could cling to.
“This is the first direct evidence for oxygen-rich marine environments during Snowball Earth,” said Dr. Maxwell Lechte, now a postdoctoral researcher at McGill University in Canada. But how that oxygen got into the oceans in the first place was a mystery. The atmosphere is a major source of oxygen for the oceans, and with the ice sheets of Snowball Earth acting as giant air-blocking shields, oxygen in seawater should’ve been nonexistent. “This could’ve led to anoxic oceans, which could’ve killed off life-forms that need oxygen to survive.” Dr. Lechte said. “It presents a bit of an unsolved problem.”