The breakup of Rodinia about 750 million years ago formed the Panthalassa ocean, with rocks that eventually became Japan sitting on its eastern margin.

[2] In the Early Silurian (450 million years ago),[3] the subduction of the oceanic plates started, and this process continues to the present day, forming a roughly 400 km wide orogeny at the convergent boundary.

The early stages of subduction-accretion have recycled the continental crust margin several times, leaving the majority of the modern Japanese archipelago composed of rocks formed in the Permian period or later.

[4] Around 16 million years ago, in the Miocene period, a peninsula attached to the eastern coast of the Eurasian continent was well formed.

In northwest[vague] Japan, the thick Quaternary deposits make determination of the geological history especially difficult.