Scientists have revived microbes from inside giant gypsum crystals located in the Naica mountain caves in Mexico. The microbes are thought to have been encased in the crystals at least 10,000 years ago, and possibly up to 50,000 years ago. See here.
The caves were opened about 100 years ago and the environment is hot (40-60C), acidic and humid with no light. Extremophile chemosynthetic microbes were found on the cave walls but it was a surprise to researchers to find bacteria and archaea in the gypsum crystals.