More than 1,300 archaeological sites are known throughout Abu Dhabi Emirate. These vary in size and importance from simple scatters of pottery or marine shells to large stone-built structures. The earliest evidence of human presence in Abu Dhabi is from Jebel Barakah, where stone tools believed to date from between 150,000 to 200,000 years ago have been identified. The first major settlements and burial sites, which occur on the islands off the coast of Abu Dhabi, are dated to around 7,500 years ago. Excavations on the islands of Marawah and Dalma confirm that these people kept domestic livestock, exploited marine resources and traded with the Ubaid civilisation of southern Mesopotamia.