The water also carries the specific fingerprint of the sulfur-rich compound sulfate—a carryover from when the water was part of the ocean—the study found.
"This same creativeness in getting energy might be found elsewhere," and might have been helpful during difficult times, such as an ancient period known as snowball Earth, Mikucki said.
During this phase, around 700 million years ago, the whole planet seems to have been periodically covered with a thick layer of ice, and the oceans were likely rich in iron.
Findings to be published in tomorrow's edition of the journal Science.
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