Here we see a river with rocky slopes and a grassy slope in the background.

 Here we see a river with rocky slopes and a grassy slope in the background.

The scientists focused on 575 artifacts made of obsidian at a site known as Simbiro III in Melka Kunture. These ancient tools came from a layer of sand dubbed Level C, which fossil and geological data suggest is more than 1.2 million years old.

These obsidian artifacts included more than 30 hand axes, or teardrop-shaped stone tools, averaging about 4.5 inches (11.5 centimeters) long and 0.7 pounds (0.3 kilograms). Ancient humans and other hominins may have used them for chopping, scraping, butchering and digging.

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Obsidian proved far more rare at Simbiro III before and after Level C, and scarce in other Melka Kunture sites. The new excavations also revealed that Level C experienced seasonal flooding, with a meandering river likely depositing obsidian rocks at the site during this time of Level C. Obsidian axes from this level were far more regular in shape and size, which suggests mastery of the manufacturing technique.