While conventional wisdom holds that early life was probably restricted to deep sea vents sprinkled thinly across the ocean floor, new research suggests this view may be way conservative. Early Earth may, in fact, have been crawling with life, in subterranean, hydrogen-rich waters that exist across vast swaths of the continental crust.
That's the finding of researchers at the University of Toronto, who last week announced their discovery of potentially life-bearing waters trapped kilometers beneath the surface in pre-Cambrian shield rocks—the oldest geologic formations on Earth. The findings have sweeping implications for the emergence of life on early Earth, the abundance of life in Earth's deep biosphere today, and the potential for life to emerge on geologically similar planets, including Mars.
In their paper, which appears in Nature, the researchers mapped hydrogen-rich waters in rock fractures from 19 different mine sites in Canada, South Africa, and Scandinavia. The waters have chemistry similar to that found near Earth's deep sea vents, suggesting these rocks may also have harbored single cell life eons ago.
Until now, estimates of the global hydrogen production sustaining early-Earth microbes didn't include contributions from ancient continents at all.
"This represents a quantum change in our understanding of the total volume of Earth's crust that may be habitable," said study co-author Sherwood Lollar in a press release last week.
The study adds to a growing pool of recent research detailing the myriad habitable spots in Earth's deep biosphere. The global network of sites identified by the researchers will undoubtedly be targeted for exploration of deep life in the coming years.
What's more, the work sheds light on how life might persist on Mars, our geologic cousin which also contains ancient rocks with hydrogen-producing potential.
"If the ancient rocks of Earth are producing this much hydrogen, it may be that similar processes are taking place on Mars," said Lollar.
With last week's discovery of organic molecules and methane—life's precursors—on Mars, the ruddy planet seems to have comfortably secured its place as our most promising candidate for extraterrestrial life.