Boston, MassachusettsCreatures that thrive on iron, sulfur, and other chemicals have been found trapped inside giant crystals deep in a Mexican cave. The microbial life-forms are most likely new to science, and if the researchers who found them are correct, the organisms are still active even though they have been slumbering for tens of thousands of years.
If verified, the discovery adds to evidence that microbial life on Earth can endure harsher conditions in isolated places than scientists previously thought possible. (See “Life Found Deep Under Antarctic Ice for First Time?”)
“These organisms have been dormant but viable for geologically significant periods of time, and they can be released due to other geological processes,” says NASA Astrobiology Institute director Penelope Boston, who announced the find today at a meeting of the American Association for the Advancement of Science. “This has profound effects on how we try to understand the evolutionary history of microbial life on this planet.”
At the same time, the microbes raise some serious concerns about efforts to explore other worlds in our solar system and hunt for alien life, she says. NASA takes many rigorous steps to sterilize spacecraft when necessary, but there are always risks that a mission to drill into another world could carry invasive—and highly durable—Earth creatures along for the ride. (See “Going to Mars Could Mess Up the Hunt for Alien Life.”)
“How do we ensure that life-detection missions are going to detect true Mars life or life from icy worlds rather than our life?” Boston asks. “Aspects of my work illustrate the extreme toughness of life on Earth and the restrictions that places on us.”
The microbes are adapted to survive in the extreme environments inside the Cave of Crystals, part of the Naica mine in the northern state of Chihuahua. Operations to haul up lead and silver involved pumping groundwater out of the vast underground caverns, which revealed a labyrinth of massive milky-white crystals, some reaching more than 30 feet long.
Boston took samples from pockets of fluid trapped inside the crystals in 2008 and 2009, under the auspices of New Mexico Tech. Her team was able to "wake up" dormant microbes in that fluid and grow cultures, she revealed today at the meeting. The organisms are genetically distinct from anything known on Earth, according to her team’s analysis, although they are most similar to other microbes found in caves and volcanic terrain.
Previous work dated the oldest crystals in the cave at half a million years. Based on those calculations for the crystal growth rate, her team thinks the organisms they have growing in the lab had been inside their glittering cocoons for somewhere between 10,000 and 50,000 years.
The work is currently being written up for publication and has not yet gone through the peer-review process, the standard first step in verifying a scientific find. That makes it hard for other experts to say much about the claim for now.
“But, reviving microbes from samples of 10,000 to 50,000 years is not that outlandish based on previous reports of microbial resuscitations in geological materials hundreds of thousands to millions of years old,” notes Brent Christner, a microbiologist at the University of Florida in Gainesville.
For instance, other scientists have reported on ancient microbial life found in glacial ice, encased in amber, and trapped in salt crystals. “However, the amount of skepticism associated with these studies usually correlates directly with the age of the claim,” cautions Christner.
Part of the problem is that no one is sure how long life of any kind can survive when dormant. Even sleeping organisms need food eventually or their cells will start to degrade, and scientists don’t yet know if these hardy microbes can slow down their metabolism just enough to survive for millennia.
It’s possible the organisms from Naica are eking out a living using the limited energy sources in the fluids in which they were found, Christner adds: “Perhaps they are surviving by eating dead microbes that weren’t so lucky.”
But there’s also a chance that the Naica microbes didn’t come from inside the crystals at all, but from the pools of water surrounding them.
In 2013, researchers in France and Spain reported the discovery of microbial life in hot, saline springs deep inside the Naica system. These modern-day microbes also get their energy from chemicals in the subsurface and are also genetically distinct from known microbial species.
“I think that the presence of microbes trapped within fluid inclusions in Naica crystals is in principle possible. However, that they are viable after 10,000 to 50,000 years is more questionable,” says microbiologist Purificación López-García of the French National Center for Scientific Research, one of the co-authors of the 2013 study.
“Contamination during drilling with microorganisms attached to the surface of these crystals or living in tiny fractures constitutes a very serious risk,” says López-García. “I am very skeptical about the veracity of this finding until I see the evidence.”
Boston notes that her team took a variety of steps to try and avoid contamination, including wearing protective suits, sterilizing their drills, and sterilizing the surfaces of the crystals with hydrogen peroxide and, in some cases, fire.
"We have also done genetic work and cultured the cave organisms that are alive now and exposed, and we see that some of those microbes are similar but not identical to those in the fluid inclusions," Boston says. That gives the team additional confidence that they are seeing organisms from inside the crystals.
Unfortunately, going back to the cave to collect more samples would be a tricky task. The mine stopped being profitable and operations at Naica have ceased, so the crystal cave is once more flooded with groundwater. But Boston notes that the cultures her team collected are still actively growing, and she hopes other scientists will keep studying the creatures.
“Since I have stepped into a NASA management role now, my time for science is quite limited,” Boston says. The microbes her team collected, she adds, are “a precious resource, and we want to make it available to other folks. There’s still a lot of work to do to infer anything about their history and movement and genetic relations.”