What did Earth look like 3.2 billion years ago? New evidence suggests the planet was covered by a vast ocean and had no continents at all.

Continents appeared later, as plate tectonics thrust enormous, rocky land masses upward to breach the sea surfaces, scientists recently reported.They found clues about this ancient waterworld preserved in a chunk of ancient seafloor, now located in the outback of northwestern Australia. 

What does the study say?

In the new study, Johnson and co-author Boswell Wing, an associate professor of geological sciences at the University of Colorado Boulder, turned to Panorama’s unique landscape in the Australian outback. Its rocky scenery preserves a hydrothermal system dating to 3.2 billion years ago, “and records the entire ocean crust from the surface down to the heat engine that drove circulation,” Johnson said. Preserved in that craggy seafloor were different versions, or isotopes, of oxygen; over time, the relationship between these isotopes can help scientists decode shifts in ancient ocean temperature and global climate. However, the scientists uncovered something unexpected through their analysis of more than 100 sediment samples. They found that 3.2 billion years ago, oceans held more oxygen-18 than oxygen-16 (the latter is more common in the modern ocean). Their computer models showed that on a global scale, continental land masses leach oxygen-18 from the oceans. In the absence of continents, the oceans would carry more oxygen-18. And the ratio between these two oxygen isotopes hinted that at the time, there were no continents at all, the study found.

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