Question

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?

Answer 1

You might be interested in this resource: The Clock of the Long Now.

The Clock of the Long Now, also called the 10,000-year clock, is a proposed mechanical clock designed to keep time for 10,000 years.

In building it they discuss relevant topics such as:

Longevity: The clock should be accurate even after 10,000 years, and must not contain valuable parts (such as jewels, expensive metals, or special alloys) that might be looted.
Maintainability: Future generations should be able to keep the clock working, if necessary, with nothing more advanced than Bronze Age tools and materials.
Transparency: The clock should be understandable without stopping or disassembling it; no functionality should be opaque.
Evolvability: It should be possible to improve the clock over time.
Scalability: To ensure that the final large clock will work properly, smaller prototypes must be built and tested.

The solution they are building is far from trivial