During the Ice Age from about 35,000 years ago
until about 11,600 years ago,
sea levels were lower due to the water in the glaciers.
At the peak of glaciation, about 18,000 years ago,
sea level was about 85 meters lower than it is now
(which is about 50 meters lower than it was when
the Ice Age ended about 11,600 years ago).
Clear evidence of Ice Age Civilization
in the period of 35,000 to 12,000 years ago
is found in Fukui Cave of Northern Kyushu Island,
the southwesternmost island of Japan,
in the form of Jomon pottery containers, which
(according to Joseph B. Lambert's book
Traces of the Past (Addison-Wesley 1997))
have been dated as slightly later than
12,750 +/- 500 years old,
and therefore consistent with coinciding with
the end of the Ice Age about 11,600 years ago,
so that the Jomon pottery could have been taken
to Fukui Cave of Kyushu by Jomon people
of the Ice Age Civilization when they fled
the flooding of the surrounding lowlands
after the Ice Age ended around 11,600 years ago.