Goa's history goes back 20,000–30,000 years. The rock art engravings exhibit the earliest traces of human life in India.p.254 Upper Paleolithic or Mesolithic rock art engravings have been found on the bank of the river Kushavati at Usgalimal. Petroglyphs, cones, stone-axe, and choppers dating to 10,000 years ago have been found in many places in Goa, such as Kazur, Mauxim, and the Mandovi-Zuari basin. Evidence of Palaeolithic life is seen at Dabolim, Adkon, Shigao, Fatorpa, Arli, Maulinguinim, Diwar, Sanguem, Pilerne, and Aquem-Margaon etc. Difficulty in carbon dating the laterite rock compounds poses a problem for determining the exact time period.