Early Earth was no barren, lifeless landscape. Instead, it may have been covered entirely with water.
Welcome to the Waterworld.
Rocks aged 3.24 billion years reveal the Earth may have had absolutely no surface land at at least
Early Earth was no barren, lifeless landscape. Instead, it may have been covered entirely with water.
Welcome to the Waterworld.
Rocks aged 3.24 billion years reveal the Earth may have had absolutely no surface land at at least one point in its early history, according to a new study.
Taken from the former oceanic crust of Western Australia, the ancient rock samples contain oxygen isotopes consistent with an entirely oceanic environment, suggesting that Earth was once composed of one giant, globe-spanning ocean.
The study was published on Monday in the journal Nature Geoscience.
Oceans in the desert
The study uses data from more than 100 rocks taken from the Australian outback’s Panorama district. These days, the area is desert-like, lead author Benjamin Johnson, assistant professor Iowa State University, said in a statement. But that wasn't always the case.
"Today, there are these really scrubby and rolling hills that are cut through by dry river beds," Johnson said. "It's a crazy place."
“There are no samples of really ancient ocean water lying around,” Johnson said, “but we do have rocks that interacted with that seawater and remembered that interaction.”
That's where the oxygen isotopes come in. The rocks “remember" signatures of the early ocean in levels of oxygen isotope Oxygen-18. Our modern oceans are enriched in this isotope, too, but the data reveal that these early oceans had significantly higher levels of the isotope.
The isotopes' presence exposes some intriguing details about this early oceanic Earth. Levels of Oxygen-18 in the seawater decreased over time, the researchers say. But at the same time, levels of the isotope in marine sediments — the remains of life that can now be found on the dried-up sea floor — increased. The researchers propose that, as the landscape evolved some 3 to 2.5 billion years ago (in a process called continental weathering), the Oxygen-18 levels were driven down, bringing them in line with the level found in our oceans now.
The results suggest the Earth's water cycle and how it influenced the formation of the continents may be more complicated than scientists previously believed. It may be that the water cycle went through two "steady states" — one before the continents formed, and one after.
The data also enables scientists to zoom in on what different forms o