Earth could have been an actual ‘waterworld’ in its infancy, scientists say

BOULDER, Colo. — Evidence gathered by researchers at the University of Colorado Boulder shows that newly-formed Earth could have been almost entirely covered by water — a so-called “waterworld” much like the post-apocalyptic planet depicted in the widely panned cult classic sci-fi film starring Kevin Costner.

Using hydrothermal chemistry data, the researchers were able to conceive of what the Earth’s surface looked like 3.2 billion years ago. The findings may also help other scientists understand how single-cell organisms first evolved and under what conditions.

Benjamin Johnson
Benjamin Johnson inspects an outcrop in the Panorama district by what was once an ancient hydrothermal vent. (Photo credit: Jana Meixnerova)

“The history of life on Earth tracks available niches,” explains co-author Boswell Wing, an  associate professor in the Department of Geological Sciences at CU Boulder, in a university release. “If you’ve got a waterworld, a world covered by ocean, then dry niches are just not going to be available.”

Scientists have long debated whether the early Earth was once far hotter than it is now.

“There was seemingly no way forward on that debate,” notes lead author Benjamin Johnson, a postdoctoral researcher in Wing’s lab. “We thought that trying something different might be a good idea.”

Wing and Johnson studied a geologic site in the Northwestern Australian Outback called the Panorama district, where a 3.2 billion-year-old chunk of ocean crust lies turned on its side. The massive rock reveals the base of the ancient crust and areas where water once emerged via hydrothermal vents in the seafloor.

“There are no samples of really ancient ocean water lying around, but we do have rocks that interacted with that seawater and remembered that interaction,” says Johnson.

For the scientists, the process of analyzing these historically-rich rock formations is similar to analyzing coffee grounds. The researchers are able to extract information about the chemistry of the water that poured through it. They gathered data from more 100 rock samples from the Panorama District for the study.

Benjamin Johnson
A vista of the Panorama district looking down from the top of the ancient ocean crust to its base. (Image credit: Benjamin Johnson)

What they sought out were two different types of oxygen trapped in the rock: the slightly heavier Oxygen-18 and a lighter atom called Oxygen-16. They found that the ratio of these two oxygen isotopes was out of balance in early-Earth seawater 3.2 billion years ago. There were slightly more Oxygen-18 atoms than Oxygen-16 atoms.

Today’s landmasses absorb more Oxygen-18 atoms because of their clay-rich soil. The researchers hypothesized that the reason ancient oceans had more Oxygen-18 in them was that there weren’t as many landmasses to absorb them. They’re careful to point out, though, that this doesn’t mean there was no dry land back then.

“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 findings leave a big question behind: when did plate tectonic forces start creating landmasses? Wing and Johnson don’t have the answers yet, but they’re planning on examining younger rock formations in sites all over the world to find evidence of when landmasses started to form.

The study is published in Nature Geoscience.

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