Scientists Suggest That Earth Was Covered Entirely With Water 3.2 Billion Years Ago
takyon writes:
3 Billion Years Ago, the World Might Have Been a Waterworld, With No Continents At All
Evidence from an ancient section of the Earth's crust suggest that Earth was once a water-world, some three billion years ago. If true, it'll mean scientists need to reconsider some thinking around exoplanets and habitability. They'll also need to reconsider their understanding of how life began on our planet.
[...] The work is focused on an area in the Australian Outback called the Panorama district. In that region in northwestern Australia there's a slab of ocean floor 3.2 billion years old, that's been turned on its side. The chunk of crust holds chemical clues about ancient Earth's seawater.
[...] Marine sediments have been well-studied over time, but the authors of this study looked at the ancient crust instead. The ancient oceans held different types of oxygen that were then deposited into the crust. The scientists gathered over 100 samples of the ancient rock and analyzed it for two oxygen isotopes: oxygen-16 and oxygen 18. They wanted to find the relative amount of each isotope in the ancient crust, to compare it to the amounts in the sediment.
Their results showed more oxygen-18 in the crust when it was formed 3.2 billion years ago, meaning the ocean at that time had more oxygen-18. The pair of researchers say that means that when that crust formed, there were no continents. This is because when continents form, they contain clays, and those clays would have absorbed the heavier oxygen-18. So if there had been continents 3.2 billion years ago, their crust samples would have held less oxygen-18. The over-arching conclusion of their work is that the Earth's oceans went through two distinct states: one prior to continents forming, and one after continents formed.
Also at University of Colorado Boulder and Popular Mechanics.
Limited Archaean continental emergence reflected in an early Archaean 18O-enriched ocean (DOI: 10.1038/s41561-020-0538-9) (DX)
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