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Mars used to be a wildly different land.

Though the red planet is bone dry today, NASA's Curiosity rover recently rumbled by poignant evidence of an ancient watery world. The car-sized robot snapped an image of a unique rock that looks like its composed of stacked layers. Such a rock likely formed "in an ancient streambed or small pond," the space agency wrote.

Curiosity is winding up through the foothills of the three-mile-tall Mount Sharp, where it's encountering a place where these streams and ponds once carried red sediments through the landscape. Ultimately, some of these sediments were deposited in stacks.

And at lower elevations, there's clear evidence that Mars didn't just have ponds — it was warm and moist enough to harbor big lakes.

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Curiosity's robotic sibling, the Peservance rover, is now journeying through the planet's Jezero Crater, a place NASA suspects contained a lake and river delta. Though the water is all gone today, the robot has specialized equipment intended to identify past hints of microbial life that could have potentially dwelled on a wetter, different Mars.

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