As a result of natural erosion and deposition, Nok terracottas were scattered at various depths throughout the Sahel grasslands, causing difficulty in the dating and classification of the mysterious artifacts. Luckily, two archaeological sites, Samun Dukiya and Taruga, were found containing Nok art that had remained unmoved. Radiocarbon and thermo-luminescence tests dated the sculptures to a range of dates between about 2,900 and 2,000 years ago, making them some of the oldest in Western Africa. Many further dates were retrieved in the course of new archaeological excavations, extending the beginnings of the Nok tradition even further back in time.