A deer rib pulled from an ancient butchery site in central China carried an unexpected clue. Inside the bone, calcite crystals had grown over time, and those crystals turned out to be a kind of clock. When scientists measured them, they found that some of the stone tools at Lingjing were made about 146,000 years ago, during a harsh glacial stretch of the Pleistocene, not during a milder warm period as many researchers had assumed. That shift of roughly 20,000 years may sound modest. It changes the setting completely. “People often imagine creativity as something that flourishes in good times,” said Yuchao Zhao, assistant curator of East Asian archaeology at the Field Museum in Chicago and lead author of the research published in the Journal of Human Evolution. “Finding out that these stone tools were made during a harsh ice age tells a different story. Hard times can force us to adapt.” The finding matters because Lingjing has already become one of the most important sites for understanding ancient humans in East Asia. Excavations there, …