Places without life on Earth could facilitate the search for life on Mars

It is believed that even in the harshest environments on our planet, microorganisms seem to coexist and thrive everywhere, from the depths of the oceans to the summit of Mount Everest. However, in recent years, scientists have found two places on Earth where life is supposed to exist at all.

The first was discovered in Antarctica in June, in a desert area near the Shackleton glacier, where researchers found a series of conditions that prevent microorganisms from living: extreme cold, dry soil and the presence of toxic salts.

According to experts, the combination of these three factors completely limits the prospects for the prosperity of life. Among the more than 200 soil samples taken from the glacier, no traces of living organisms were found.

“It has long been assumed that microbes are resistant, and can live anywhere,” said Noah Ferrer, a microbial ecologist at the University of Colorado at Boulder, whose team has studied Antarctic soils.

How to take samples on Mars

The discovery, published in May in the journal JGR Biogeosciences, could help guide the search for life on Mars, where Antarctic soil has been frozen, saturated with toxic salts and has not harbored large amounts of liquid water for at least two million years. Similar to the soil of Mars.

Samples were taken in January 2018 during an expedition to a remote area in the Transantarctic Mountains. Scientists camped on the Shackleton glacier and used a helicopter for the group, which took them to the highest parts, more than 2,000 meters above sea level.

Byron Adams, a Brigham Young University biologist and project manager, recalls that while collecting samples, the soil was strewn with red volcanic rock, punctured and polished by centuries of wind erosion.

When scientists studied the rocks, they found that its lower side was covered with white salts, especially toxic crystals of perchlorate, chlorate and nitrate. Perchlorates and chlorates are reactive caustic salts used in rocket fuels and industrial chlorates, and they are abundant on the surface of Mars.

“Obviously we advocate using these kinds of places to study what life might be like on Mars or elsewhere in the universe,” Adams said. He added that if there are organisms that can live here and deal with this environment, “maybe they can live on a planet like Mars.”

Danakil Desert

In 2019, a French-Spanish team of scientists already suggested that there are places on Earth where no kind of life can thrive.

In an article published in Nature Ecology & Evolution, researchers concluded that in the Dallol geothermal complex, one of the most dangerous and inhospitable environments on our planet, located in the Danakil Desert (Ethiopia), there is no trace of microbial life. .

Experts collected a large number of samples in four different areas of the geothermal complex between 2016 and 2018. Although initial analyzes showed traces of bacteria and archaea, scientists believe these are red herrings because most of them were related to laboratory pollutants, and it is likely that Others are bacteria introduced by humans during excursions and tourist visits to the site.

“After analyzing many more samples than in previous works, with adequate controls to avoid contamination and a well-calculated methodology, we verified that there is no microbial life in these salty, hot and acidic ponds, nor in the adjacent salt lakes rich in magnesium,” said Purificación Lopez Garcia. , chief working and biologist at the National Center for Scientific Research (CNRS).

The team identified two major physicochemical barriers that prevent life from thriving in the presence of liquid water on Earth and possibly elsewhere.

The first barrier is a high level of magnesium, which is able to destroy any type of cell formation due to a phenomenon known as alternating activity. The second corresponds to a lethal combination of hyperacidity and salinity, in which simultaneous molecular adaptations to very high and low pH are impossible.

life limits?

The authors of the two studies try to be cautious in their conclusions, as there is a remote possibility that there are too few microbes in the samples for either method to detect them.

“We can’t say the soil is sterile. Nobody can say that,” Ferrer said of Shackleton Glacier. “It’s an endless search. There’s always another way or a different way to try,” he added.

The findings also raise questions about how to explain negative scientific findings, especially in the search for life on other planets. The challenge goes back to the philosophical question “How do you prove something negative?”

Likewise, the evidence presented by the Dallol Pools research group shows that there are places on Earth’s surface that are “sterile even if they contain liquid water,” Lopez Garcia emphasized. This means that the presence of liquid water on a planet, which is often used as a standard for living, does not directly mean that it has life.

Both studies provide a more in-depth understanding of the limits of life on Earth and require caution when interpreting morphological biosignatures on the planet and beyond. This indicates that the cellular or ‘biological’ aspect of the structure should not be trusted, as it may have an abiotic origin. (Text and Image: RT)