Scientists have just made a major discovery in a cave in Naica, Mexico: microbial life that could be 50,000 years old. The cave system is well known for its beauty and its intense heat, leading many to call it both Fairyland and hell. Now, it may hold some pretty amazing scientific secrets.

Scientists found ancient microbes within the cave, which probably survived thanks to the rich supply of iron and manganese in the cave. The findings were presented at the American Association for the Advancement of Science conference in Boston. The findings haven’t yet been published, however.

THe life forms appear to be 40 different strains of microbes and viruses, and they aren’t closely related to any other organism on Earth, meaning they must have evolved in isolation for a very long time.

The Naica caves stretch 800 meters into the Earth. They used to be home to lead and zinc mines, and before human arrival they were basically cut off from the outside world entirely. The caves are filled with crystals lining walls of iron, and scientists had to wear what were basically space suits to endure the intense heat.