When Adam Smith wrote that humans have bartered and exchanged from times immemorial he was making a statement about a unique characteristic of the human communities. Unlike other animals’ humans barter and exchange goods with outsiders. It is relatively easier to write a history of exchange. This can be judged from the fact that if some objects (stones in this context) are found which are not available locally; one can presume that they have been procured from other communities who live in those areas.
Although that, too, will not be true in all cases, this is because we know that hunting-gathering communities are mobile groups. This means that they might have picked up those stones during their seasonal migrations. When our ancestors realised the potential and possibilities of stone for shaping tools, they began looking for stones that could give sharper edge and had longer life. Obsidian is one such stone. But it is a rare type of stone. About 130,000 years ago two sites in Tanzania have yielded evidence for the use of obsidian. This stone had been obtained from Kenya’s Central rift valley located at a distance of 300 kilometers. Hunters moved around quite a lot. So, obsidian could have been obtained during a hunting expedition. It is a solitary evidence.