Sometimes, the greatest challenges in science come from discovering nothing.
This is what a team of biologists encountered during their search for microbes in the rugged mountain ranges of Antarctica. When they reached the most remote and desolate sites, they didn’t find any microbes — the samples they collected were fully inorganic soil.
This (non) discovery has major implications in the search for alien life, especially on Mars. It also touches on a core challenge in the philosophy of science: How should scientists interpret negative results?
A “Massively Contaminated” Planet
Searching for microbes — a.k.a microorganisms — on Earth doesn’t usually leave you with nothing to show for your efforts. According to Discovery.com, a spoonful of ordinary soil has billions of microbes, and even samples from the harshest deserts will yield thousands of them.
Microbes have been found in hot springs with water at near boiling-point temperatures, and they can even survive in airless space. As one biologist told IFLScience, “This is Earth. This is an environment that is massively contaminated with life.”
This is precisely why microbial ecologist Noah Fierer and doctoral candidate Nicholas Dragone expected to find something when they tested Antarctic soil samples for the presence of life. At first, while working their way up the slopes of the Transantarctic Mountains above Shackleton Glacier, they did find traces of hardy microbes.
According to National Geographic, as the exploration team helicoptered to higher slopes, signs of life dwindled in the samples they collected. Finally, at a windswept elevation of 7,000 feet on Schroeder Hill and Roberts Massif, the samples registered no signs of life at all.
Something Must Be Wrong, Right?
Life on Earth is so pervasive that Fierer’s first reaction to the negative results was to suspect a problem with equipment or experimental techniques. However, additional tests using a variety of methods continued to come up with nothing. Inorganic soil is not supposed to be found on Earth, but there it was.
If finding nothing is challenging, interpreting it is even more challenging. A basic general principle in scientific investigation is that absence of evidence is not the same thing as evidence of absence. The absence of evidence may simply mean the investigators did not look in quite the right place with quite the right tools. In this particular case, a handful of microbes may simply have eluded detection.
While it cannot be proven that the samples Fierer and Dragone collected are absolutely sterile, it can certainly be said that the environments in the upper reaches of Schroeder Hill and Roberts Massif are not very hospitable to life. These environments also have much in common with the surface of Mars — except that Mars is even less hospitable to life. In the cold and extremely arid environment, corrosive salts can build up over eons without ever being washed away by liquid water.
As one scientist told National Geographic, “The top surface layers of Mars are awful. We don’t have an organism on Earth that could survive on the surface.” But even a few inches below the surface, conditions may not be so hostile.
Still, the implication is that the search for life on Mars, and perhaps for alien life anywhere, may be a more challenging task than expected based on what’s known about life on Earth. Proving a negative may be a philosophical quandary, but negative findings can legitimately be introduced as part of the burden of proof in a scientific inquiry.
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