In 99th Adhyay of Udhyog-Parv of Mahabharat.
When Krishna went to Hastinapur as a peace delegate.
In the assembly of Hastinapur, Devrishi Narad told a story about his visit to Patal-Lok with Matli (charioteer of Lord Indra).
Here, he describes an EGG which is placed in Patal-Lok, which is of unknown origin and is said to detonate at the time of Pralay (Pralay-Kal).
This is a rough translation about what Devrishi-Narad said:
This egg has been placed beneath the ocean. Since the time of creation, this egg has neither broke nor has moved. No one is aware of its parentage or family or origin. It is being said that, at the time of apocalypse (Pralay-Kal), a huge fire will emerge from its core, that will burn through all the sentient and non-sentient species of all three worlds, destroying all three worlds with it.
Refer to the images below for actual verses and hindi translation
My question is: Are their any more references or description about this EGG, anywhere else.
To me, this seems like some kind of nuclear time-bomb placed in Patal-Lok (or ocean bed), that will detonate and cause the apocalypse.