When did communities first make the switch from currency with an inherent value (gold coins or gold backed paper money) to a currency that derived its value from government regulation and mutual trust?
Probably as soon as it was introduced in China.
In China in the Xth century BC, cowrie shells were used for exchange and as unit to measure value. The quality of the shell was apparently irrelevant. Then they make shells using bones and bronze (VIIth-VIth) century BC. Again their value does not seem to depend on the weight nor the precise composition. That is also true for the spade and knife money used a little later. (Weight and composition vary a lot more than what we observe for Mesopotamia).
We have a document of 242BC, the 18 regulations of Qin, stating that coins may not be sorted for quality, while pieces of fabric which were also used as money at the time had to have their standard size.
Source: Sur les spécificités fondamentales de la monnaie chinoise F. Thierry in Aux origines de la monnaie, éditions errance.