Dating loans money
Finally, there is a clear break from the use of bronze in barter into its undebatable use as money because of lighter measures of bronze not intended to be used as anything other than coinage for transactions.
The aes grave (heavy bronze) (or As) is the start of the use of coins in Rome, but not the oldest known example of metal coinage.
David Graeber proposes that money as a unit of account was invented when the unquantifiable obligation "I owe you one" transformed into the quantifiable notion of "I owe you one unit of something".
Due to the complexities of ancient history (ancient civilizations developing at different paces and not keeping accurate records or having their records destroyed), and because the ancient origins of economic systems precede written history, it is impossible to trace the true origin of the invention of money and the transition from "barter systems" to the "monetary systems".
Schumpeter's theory had several themes but the most important of these involve the notions that money can be analyzed from the viewpoint of social accounting and that it is also firmly connected to the theory of value and price.
There are at least two theories of what money is and these can influence the interpretation of historical and archeological evidence of early monetary systems.
Even more intellectually complicated than this example would be creating tokens that abstractly represented a claim on goods stored in a warehouse, and further still, creating metal tokens (which would require knowledge of mining & refining metal and creating coins) requires an even more evolved state of mind than any of these other examples.
In his book Debt: The First 5,000 Years, anthropologist David Graeber argues against the suggestion that money was invented to replace barter.