Early Earth, home to a number of our planet's first lifeforms, may have been a real-life "Waterworld" without a continent in sight- a discovery that can help scientists to better understand how and where single-cell organisms first emerged on Earth.
The researchers took advantage of a quirk of hydrothermal chemistry to suggest that the surface of Earth was likely covered by a worldwide ocean 3.2 billion years ago.
It may even have looked just like the post-apocalyptic, and land-free, future imagined in Kevin Costner's infamous film 'Waterworld'.
"The history of life on Earth tracks available niches. If you've got a Waterworld, a world covered by ocean, then dry niches are just not going to be available," said Boswell Wing, an professor working in the Department of Geological Sciences at the University of Colorado Boulder.
Lead author Benjamin Johnson and Wing analysed a geologic site called the Panorama district located deep in Northwestern Australia's outback.
It's also the resting spot for a 3.2 billion-year-old chunk of ocean crust that's been turned on its side.
The team looked, especially , for 2 different isotopes of oxygen trapped in stone: a rather heavier atom called Oxygen-18 and a lighter one called Oxygen-16.
The duo discovered that the ratio of these two isotopes of oxygen may are a touch off in seawater 3.2 billion years ago -- with just a smidge more Oxygen-18 atoms than you'd see today.
"Though these mass differences seem small, they are super sensitive," Wing said.
He explained that today's land masses are covered by clay-rich soils that disproportionately take up heavier oxygen isotopes from the water -- like mineral vacuums for Oxygen-18.
The team theorized that the foremost likely explanation for that excess Oxygen-18 in the ancient oceans was that there simply weren't any soil-rich continents around to suck the isotopes up.
That doesn't mean, however, that there weren't any spots of land around.
"There's nothing in what we've done that says you can't have teeny, micro-continents sticking out of the oceans," Wing said. "We just don't think that there were global-scale formation of continental soils like we have today."
The researchers saw it as a one-of-a-kind opportunity to select up clues about the chemistry of ocean water from billions of years ago.
"There are not any samples of really ancient ocean water lying around, but we do have rocks that interacted thereupon seawater and remembered that interaction," Johnson said. The study appeared within the journal Nature Geoscience.
The study also feeds into an ongoing debate over what ancient Earth may have looked like: Was the earth much hotter than it's today?
"There was seemingly no way forward on that debate. We thought that trying something different might be a good idea," said Johnson.