Quaternary era. The Olduvai Gorge, in the Ngorongoro Conservation Area, a UNESCO World Heritage Site, features a collection with remnants of tools that document the development and use of transitional technology. The indigenous populations of eastern Africa are thought to be the linguistically isolated Hadza and Sandawe hunter-gatherers of Tanzania. The first wave of migration was by Southern Cushitic speakers who moved south from Ethiopia and Somalia into Tanzania. They are ancestral to the Iraqw, Gorowa, and Burunge. Based on linguistic evidence, there may also have been two movements into Tanzania of Eastern Cushitic people at about 4,000 and 2,000 years ago, originating from north of Lake Turkana. Archaeological evidence supports the conclusion that Southern Nilotes, including the Datoog, moved south from the present-day South Sudan / Ethiopia border region into central northern Tanzania between 2,900 and 2,400 years ago. These movements took place at approximately the same time as the settlement of the iron-making Mashariki Bantu from West Africa in the Lake Victoria and Lake Tanganyika areas. They brought with them the west African planting tradition and the primary staple of yams. They subsequently migrated out of these regions across the rest of Tanzania between 2,300 and 1,700 years ago. Eastern Nilotic peoples, including the Maasai, represent a more recent migration from present-day South Sudan within the past 500 to 1,500 years. The people of Tanzania have been associated with the production of iron and steel. The Pare people were the main producers of sought-after iron for peoples who occupied the mountain regions of north-eastern Tanzania. The Haya people on the western shores of Lake Victoria invented a type of high-heat blast furnace, which allowed them to forge carbon steel at temperatures exceeding more than 1,500 years ago. Travellers and merchants from the Persian Gulf and India have visited the east African coast since early in the first millennium AD. Islam was practised by some on the Swahili Coast as early as the eighth or ninth century A.D. Medieval Bantu-speakers built farming and trade villages along the Tanzanian coast from the outset of the first millennium. Archaeological finds at Fukuchani, on the north-west coast of Zanzibar, indicate a settled agricultural and fishing community from the 6th century CE at the latest. The considerable amount of daub found indicates timber buildings, and shell beads, bead grinders, and iron slag have been found at the site. There is evidence for limited