10 Ancient Mines Abandoned After What Archaeologists Found at the Bottom

In April 2000, workers at the Naica silver mine in Mexico broke through a limestone wall and found the Cave of Crystals, selenite formations up to 36 feet long that took between 500,000 and 600,000 years to grow. On the cave walls, in sections where crystal growth had partially covered their edges, were geometric marks. Working backwards from known selenite growth rates, researchers estimated the marks were made between 30,000 and 50,000 years ago. In 2015, when zinc prices fell, the company stopped pumping and the cave reflooded within months. No comprehensive photographic record of the marked sections was made before the water returned. The images that exist are fragmentary. The most relevant sections, deepest in the cave, most heavily covered by crystal overgrowth, are precisely the sections least documented.
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