Oldest known form of currency is the barter system that started in the 9000 BC.
Cows, animals, and poultry were treated as forms of exchange when currency didn’t exist. Barter system worked fine, but was not sustainable, making it difficult to store wealth.
Similar case with quantifying the value of goods, it was almost impractical until 3000BC, when Mesopotamia (modern day Iraq) Shakel was introduced, both as a unit of currency and unit of weight.
Further reading at Amazon.