Scientists drilling into a New Mexico rock formation deep underground have brought to life four unknown strains of bacteria that have lain entombed in salt crystals for 250 million years.

The bacteria, like many of their kind, form into long-lasting protective spores. The scientists were able to revive the spores until the microbes reproduced.

The report, by a team of biologists and geologists, has already fueled speculation that spores of living organisms might somehow be transported from planet to planet, across the galaxy and over eons. It is a concept known as “panspermia,” which some see as a possible source for life arising on Earth.