Final answer:
Sage's barrier decays over time, but the exact time frame is uncertain.
Step-by-step explanation:
Sage's barrier decays and eventually gets destroyed over time. Based on the given information, there are a few clues that can help estimate the time it takes for the barrier to stop decaying:
It is roughly twice as old as agriculture, so it has been decaying for a very long time.
Between 1-2% and 3% of certain quantities are mentioned, which may indicate the rate at which the decay occurs.
Sand is mentioned, suggesting that erosion might play a role in the barrier's decay.
However, without more specific information or context, it is difficult to provide a precise time frame.