Two recent studies came to opposite conclusions about the same evidence of life in a caustic pool in Ethiopia.
Extreme environments on Earth may model habitats on other planets, like the moon Titan.
The evidence of life found in Ethiopia is DNA from archaea, an organism similar to bacteria.
Live Science reports a lively he-said-she-said over the potential for life in an extreme environment around a volcano in Ethiopia. One group sought to prove a negative and demonstrate that the really hot, acidic, and salty pools don’t and can’t support life. The other faction noted the same kind of evidence, but concluded this means there is life in the pool. It’s a real methodological head-scratcher.
The point of contention is over tiny trace amounts of DNA found in the pool that belong to a category of life called archaea, or archaebacteria. Long ago, cell theory was a new and revolutionary way to look more closely at life, and scientists moved animals to one group and plants to another based on the presence of the cellulose cell wall. For over 100 years, those were the only two groups.
Over time, the study of these organism groups was like someone getting closer to the right eyeglasses prescription. There weren’t just two—there were five, and some were eukaryotes (with nucleuses), and some were prokaryotes (without). But that wasn’t complete either, and scientists made a third domain in addition to eukaryotes and prokaryotes: the archaea. Even the term “archaeabacteria” came and went with the foggy glasses, because the archaea aren’t bacteria. In 1,000 years, there will probably be 20 kingdoms just like there are 20 senses.
Environments like the caustic Dallol Volcano region were the site of many archaea discoveries, because so many extremophiles are classified as archaea. “Extremophile” is the blanket term for organisms that can survive in what we think of as inhospitable or even hostile environments. The world’s foremost microscopic bear-shaped garbage bag, the tardigrade, is an extremophile that, unusually, belongs to the animal kingdom.
Most extremophiles are bacteria or archaea. Bacteria that eat methane, called methanotrophs, have evolved to live in extreme conditions that are toxic to most other organisms. The existence of these tiny garbage eaters is part of what stokes our hope to find life in places like Saturn’s moon Titan, where the surface has actual oceans of liquid methane. Extremophiles challenge the “gut feeling” of where and how life can survive.
The disagreement over the Dallol Volcano pools sits in this same area of speculation. “In these most extreme environments, that were really acidic, hot and contained magnesium salts, the researchers found no DNA and thus no trace of a living organism,” Live Science wrote of a newer study by researchers in France. The scientists took samples and superzoomed until they found, finally, just the tiniest fragments of archaea that they believe blew over from neighboring ponds that were less severe.
This study appeared in Nature Ecology & Evolution alongside a critique of its methods. This is common—studies of extreme situations in particular are tough to design and conduct. Live Science explained the criticism: “For example, the researchers' DNA analysis couldn't determine if the detected organisms were alive or active, and it's unclear if their measurements of the water factors such as pH were done accurately.”
That could be why a similar study from just two months ago came to an opposite conclusion. “The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars,” that abstract says. "Given the risk of detecting any type of contamination, microbiologists that work in extreme environments take many precautions to avoid it," the lead researcher told Live Science.
Like significant figures and margins of error, what “counts” as living or thriving in extreme environments must be quantified specifically to avoid creating big, fuzzy areas of disagreement. Hopefully, more studies over time will eventually bear out which side of the Dallol dustup is right.