Earth's Greatest Catastrophes Seem to Follow a Mysterious 27-Million-Year Pulse https://flipboard.com/@sciencealert/earth-s-greatest-catastrophes-seem-to-follow-a-mysterious-27-million-year-pulse-4gba6blgd0gdfhgg?utm_source=flipboard&utm_medium=activitypub Posted into ScienceAlert @sciencealert-ScienceAlert