"From the mid-1970s there were new claims for the independent invention of iron smelting on central Niger and from 1994–1999 UNESCO funded an initiative "Les Routes du Fer en Afrique/The Iron Routes in Africa" to investigate the origins and spread of iron metallurgy in Africa. This funded both the conference on the early iron in Africa and the Mediterranean and a volume, published by UNESCO, that has generated much controversy because it included only authors sympathetic to the view that iron was independently invented in Africa. Two major reviews of the evidence were published in the mid-2000s. Both authors concluded that there were major technical flaws in each of the studies claiming the independent invention. Three major issues were identified. The first was whether the material dated by radiocarbon was insecure archaeological association with iron-working residues. (Many of the dates from Niger, for example, were on organic matter in potsherds that were lying on the ground surface together with iron objects). The second issue is the possible effect of "old carbon" - wood or charcoal much older than the time at which iron was smelted. This is a particular problem in Niger, where the charred stumps of ancient trees are a potential source of charcoal and have sometimes been misidentified as smelting furnaces. A third issue is the inherent lack of precision of the radiocarbon method itself in the range from 800 to 400 BC, which is attributable to the irregular production of radiocarbon in the upper atmosphere. Unfortunately, most radiocarbon dates for the initial spread of iron metallurgy in sub-Saharan Africa fall within this range."
