Supernova
The "local bubble" is a ballooning region of hot gas, 600 light-years across. It surrounds the Solar System and dominates our stellar neighbourhood. It was formed by over a dozen supernovae blowing up in a nearby moving clump of stars. This happened between 2.3 million and 1.5 million years ago. This roughly corresponds with the start of the Pleistocene ice ages. The connection may be accidental.