Mars Didn't Have Bathtubs, It Had Shelves

Graphic showing the process of ocean ring deposition on Mars. Credit - A.S. Zaki & M.P. Lamb

Scientists have been debating for decades whether Mars once held a vast ocean covering a large part of its northern face. To prove the idea, they’ve been looking for a “bathtub ring” - a distinct, level shoreline that shows where water once stood. But, despite years of looking, they’ve only been able to find a very distorted potential shoreline whose height deviates by several kilometers - not exactly great evidence of a stable water level. But, according to a new paper in Nature from Abdallah Zaki and Michael Lamb of CalTech, what scientists should have been looking for wasn’t a bathtub ring, but a continental shelf.

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