FWIW, this paper states that based on the measurements of 60Fe deposition on the ocean floor, that it provides evidence of a possible 2.2 million year old supernova located at a distance between 20-430 light years. They also report the possibility of 16 supernova events in the past 13 million years within 320 light years of the Local Bubble.
Basically, the though is that supernovae less than 200 parsecs away are estimated to occur every 100,000 years or so (Fields, B. D.; Ellis, J. (1999). "On Deep-Ocean Fe-60 as a Fossil of a Near-Earth Supernova"). Given the age of the Earth, lots of events possible throughout our even recent geological past.
Edited by BillP, 25 August 2019 - 06:17 PM.