A user posted an answer on the world building stack exchange about the possibility of long dormant fungal spores coming to life.

I was curious to learn more (no sources were given) and finally came across another world building answer linking to a google book result.

The oldest viable fungi known were isolated from the inner portions of the Greenland glacier ice cores, including glacial ice estimated as 140,000 yrs old

from Ainsworth & Bisby's Dictionary of the Fungi (2008). The cited source can be found at https://www.jstor.org/stable/3761562. (Ma, Li-Jun, Scott O. Rogers, Catharine M. Catranis, and William T. Starmer. "Detection and Characterization of Ancient Fungi Entrapped in Glacial Ice." Mycologia 92, no. 2 (2000): 286-95. doi:10.2307/3761562.)

I also came across a book, Life in Ancient Ice (2016; Princeton University Press) that references (p293) research by Ivanushkina extracting spores from permafrost. I believe a paper similar to the one mentioned can be found at https://www.ncbi.nlm.nih.gov/pubmed/22757669. Here viable Aspergillus sydowii, Chrysosporium europae, Penicillium chrysogenum approximately 7,485 ± 40 years old were found, and viable Penicillium chrysogenum approximately 23,705 ± 110 years old were found in Antarctic permafrost.