Based on radiometric dating (often potassium-argon dating), hominids began to use Acheulean techniques around 1.65 million years ago, and continued to use these tools until about 100,000 years ago. Archaeologists found the oldest known Acheulean tools in the West Turkana region of Kenya. These tools are 1.65 million years old. Some archaeologists think that hominids began to use Acheulean techniques earlier, around 1.8 million years ago.