Ancient humans didn't exactly have kitchen supplies, but still had to eat—a fact that might help solve an old mystery. In a new paper, researchers say they can explain the small stone balls found in archaeological sites across Asia, Africa, and Europe dating back nearly two million years. The key was a 30-ball cache from Israel's Qesem Cave, where people lived 200,000 to 400,000 years ago. "It all began during excavations at the cave, where I have been working since 2009," lead researcher Ella Assaf tells the Jerusalem Post. "Every now and then, in specific areas of the cave, we came across these strange tools." Oddly, the balls were made of dolomite rock or limestone, unlike the many flint tools discovered there.
So researchers analyzed the balls microscopically and found two things: wear marks and organic residue, LiveScience reports. "We were very lucky since they were able to identify residues of bone marrow, despite the fact that it is very rare to find traces of organic material after such a long time," says Assaf. Then they took to crushing bones, first with cobblestones and then the hand-sized balls. Turns out the balls were comfortable to hold and cleanly broke bones, enabling easy marrow extraction. This echoes research that Qesem Cave's ancient inhabitants ate bone marrow and stored it for up to nine weeks, per Science Alert. But whether the balls were initially made for marrow extraction remains unknown. (Read more archaeology stories.)