Geology is most probably largely how the sealed claim has been made .. it was open to the world when the limestone was forming, formed (Speleogenesis) by sky water (rain) permeating down and eating out a limestone void, and "sealed" by thick and impermeable layers of clays and loess (windborne sediment) some 2.5 million years ago during the Quaternary.

There are also genetic drift estimates, which put the "last" outside species to enter at about that time (

  One of the most recent animals recorded is the cave's only species of snail, Heleobia dobrogica, which has inhabited the cave for slightly more than 2 million years.