A trove of stone artifacts uncovered in northwestern Kenya suggests human ancestors were crafting tools 3.3 million years ago—about 700,000 years earlier than previously thought.

The tools, described at the Paleoanthropology Society’s meeting in San Francisco this week, are in the form of flakes—sharp stone fragments that could be used for cutting, as well as the cores from which flakes were struck, and anvils, used to hold the cores during the knapping process. Overall, more than 130 artifacts have been recovered from the site, called Lomekwi 3, said Stony Brook University archaeologist Sonia Harmand, and some of them are quite large, weighing more than 30 pounds.

The origin of tool-making is long-thought to begin only with the