Ever since the Ancient Earth Era, the island of Japan had been sliding toward the Mariana Trench every year. Also, Japan itself was a country with many earthquakes, and each earthquake would exacerbate the problem, accelerating this process further.
At that time, the scientists had already speculated that a few thousand years later, the entire Japan sink into the Mariana Trench, never appearing on the ocean's surface again. However, ten thousand years had passed and not only did Japan not vanish, but the Japanese seemed to flourish and become even more prosperous.
The prediction of the scientists wasn't actually wrong. Such a situation didn't occur because of the change in era. Thus, new technology was developed which prevented that from happening.
