Truly lifeless?

Scientists have discovered microbial lifeforms in the world’s most inhospitable environments, from the sulfur-saturated waters of an underwater volcano to the cold, dry, and irradiated environment of Earth’s stratosphere. But one research team says it has found a place in Antarctica that is so inhospitable, even these extremophile microbes may not be able to make a home.

In a recent report published in the Journal of Geophysical Research: Biogeosciences, a pair of University of Colorado microbial ecologists presented evidence that certain portions of the Transantarctic Mountains that bisect the frozen continent may be barren and lifeless. If true, sections of the region would join a tiny list of places on Earth where even microbial life may not be able to gain a foothold. Studying the Antarctic landscape may strengthen the search for life on other worlds.

The mountains that divide Antarctica are one of the few places on the continent not permanently shrouded in ice. Brigham Young University biologist Byron Adams led the January 2018 expedition to the mountain range funded by the National Science Foundation. The team battled high winds and sub-zero temperatures to take 204 soil samples from a remote valley. They traversed some of the terrain on foot and used a helicopter to take samples from higher altitudes.

Scientists chose the Transantarctic range because of its similarity to the Martian landscape. Studying microbes in the wastes of the Antarctic could give scientists ideas about where to look and how to design instruments to seek out tiny lifeforms. Like on Mars, the sandy soil of the Transantarctic stays frozen permanently and hasn’t seen any significant precipitation in recorded history. And the soil also contains caustic salts that poison the ground. “It felt like sampling on Mars,” Adams told National Geographic. He said that when shoveling, “you know you’re the first thing to disturb that soil in forever.”

When Adams’ team returned with the samples, University of Colorado microbial ecologist Noah Fierer and graduate student Nicholas Dragone began searching for signs of life. In samples from lower elevations and closer to the continent’s glaciers, the pair used a technique called polymerase chain reaction (PCR) to find tardigrades, rotifers, and other microscopic lifeforms. But as the pair began testing soils collected at higher and drier locations, they found less and less.

When PCR testing failed to reveal any microbes on the 20 percent of samples taken from the highest elevations, Fierer and Dragone began questioning the results. Dragone turned to other methods, including feeding soil samples with glucose and other chemicals to see if he could provoke anything to grow. But despite their efforts, the University of Colorado scientists couldn’t find any signs of life. “While we cannot confirm that this subset of soils is completely sterile and devoid of microbial life, our results suggest that microbial life is severely restricted in the coldest, driest, and saltiest Antarctic soils,” the researchers wrote in their report.

Canadian researcher Jacqueline Goordial discovered a similarly lifeless location in Antarctica in 2016. Her initial study found no life in soil samples taken from the McMurdo Dry Valleys. But when Goordial raised the soil temperatures just above freezing, dormant microbes in the desolate soil suddenly sprang to life, she told National Geographic. The same might be true of the samples taken from the Transantarctic Mountains, which is why neither Fierer or Dragone can say with certainty the soil is sterile.