Oceans could also be shrinking — Science Information, March 10, 1973

The oceans of the world could also be progressively shrinking, leaking slowly away into the Earth’s mantle…. Though the oceans are always being slowly augmented by water carried up from Earth’s inside by volcanic exercise … some course of reminiscent of sea-floor spreading appears to be letting the water seep away extra quickly than it’s changed.

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Scientists traced the ocean’s leak to subduction zones, areas the place tectonic plates collide and the heavier of the 2 sinks into the mantle. It’s nonetheless unclear how a lot water has cycled between the deep ocean and mantle by way of the ages. A 2019 evaluation means that sea ranges have dropped by a median of as much as 130 meters over the past 230 million years, partially as a result of Pangea’s breakup creating new subduction zones. In the meantime, molten rock that bubbles up from the mantle as continents drift aside could “rain” water again into the ocean, scientists reported in 2022. However since Earth’s mantle can maintain extra water because it cools (SN: 6/13/14), the oceans’ mass may shrink by 20 % each billion years.