Interstellar dust clouds related to snowball Earth?
The Milky Way and other spiral galaxies each house about 1,000 to 2,000 giant clouds that contain enough dense gas and dust to form hundreds of thousands of sun-like stars. According to a new model, an encounter with such an interstellar dust cloud could have triggered global glaciations on Earth that occurred 600 million and 750 million years ago.
Geotimes
This was the basis of a novel by Sir Fred Hoyle, The Black Cloud, except that in the novel, the cloud was sentient.
The premise is intriguing enough: An enormous, living cloud of matter, millions of kilometers across, descends upon the solar system and by its very presence threatens the existence of all life on Earth.