This week’s science news was full of surprising discoveries hidden deep within the Earth, including a potential answer to the age-old mystery of how Colorado River tributaries seem to defy gravity.

The Green River, which begins in Wyoming and joins the Colorado River in Utah, carved a path through the Uinta Mountains rather than bypassing them when it formed millions of years ago. Exactly how the river was able to flow “uphill” was unclear. But now geologists say they may have found an explanation: A phenomenon called lithospheric drip It pulled in mountains, helped rivers carve its way, and then bounced back to form the terrain we see today.