Suppose you have to specify the moment in time when a given event occurred, a "zero time". The record must be accurate to the minute, and be obtainable even after thousands of years. All the measures of time we currently have are relative to a well defined zero, but the zero is not easy to backtrack exactly.
One possibility would be to take a sample of Carbon with a well defined, very accurate amount of 14C, and say: the event occurred when the 14C was x%. At any time, measuring the rate of decay, you would know when the event occurred. This however, requires a physical entity to measure, which may be lost.
Another way would be to give the time lapsed after a well defined series of solar eclipses. In order to define precisely the context, you would say a list of (say) five consecutive eclipses and the places on Earth where they were total, and then a time gap from the last of the set. At any time in the future, you can backtrack the specified conditions into a celestial mechanics program and find when the event occurred.
Is there a standardized or well recognized method to do so?