If Mars had life, it might not have needed oxygen to survive – study

Earth’s oxygen rich the atmosphere does more than lay the foundation for a complex life. The oxygen in the atmosphere is so reactive that it easily combines with other chemical elements. Together they form important ores such as iron oxides and manganese oxides found in the earth’s crust. So when rovers discovered manganese oxides on Mars, scientists interpreted them as clues to Mars’ past atmosphere: it must have contained oxygen.

But a new study puts the brakes on that idea.

Both Gale Crater and Endeavor Crater contain manganese oxides. We know this thanks to the MSL Curiosity (Gale Crater) and the Opportunity Rover (Endeavour Crater.) The discovery suggested that Mars once had not only oxygen in its atmosphere, but also surface water.

“These high-manganese materials cannot form without a lot of liquid water and strong oxidizing conditions. Here on Earth, we had a lot of water, but no widespread occurrences of manganese oxides until after the oxygen level in the atmosphere rose,” says Nina Lanza, a planetary scientist at Los Alamos National Laboratory .Lanza was lead author of a 2016 study on manganese oxides on Mars.

This is a HiRISE image of Opportunity Rover’s path along the rim of Endeavor Crater. At Murray Ridge, the rover accidentally knocked over some rocks with its wheels. The rocks became targets for observation, and these observations showed the presence of manganese oxides.NASA/JPL/HiRISE

But a new study in Nature Geosciences shows how atmospheric oxygen may not have been necessary for the formation of Martian manganese oxides. The study is “Formation of manganese oxides on early Mars due to active halogen cycling.” The first author is Kaushik Mitra, who completed this work as part of his doctoral research at Washington University.

Manganese is the tenth most abundant element in the earth’s crust, and there are over 30 manganese oxide minerals. People have used them for thousands of years. Neanderthals may have used them to start fires, and Paleolithic cave artists used them in their paintings. The ancients also used them as pigments and to prepare glass. In modern times, we use them in metal ore, dry cell batteries and as catalysts in hydrogen production.

This is one of the paintings in the Lascaux caves in France, where Paleolithic artists used manganese oxides and other materials to depict the large animals that were present at the time.PHILIPPE LOPEZ/AFP/Getty Images

On Earth, they are ubiquitous in soils and sediments, and they are widespread due to the planet’s oxidizing atmosphere. They usually form “at the interface between the lithosphere and hydrosphere, atmosphere and/or biosphere,” according to a 1999 research paper. On Mars, the rovers found the manganese oxides in watery cracks and veins in the rock using X-ray spectrometry.

When rovers found them on Mars, the natural conclusion was that the conditions that created them here on Earth must have been present in some form on Mars. Mars’ ancient habitability is a topic that holds our attention, so the findings were exciting.

But the new research identified another route to manganese oxides that doesn’t require oxygen. Instead, the halogen elements chlorine and bromine lie behind Mars’ manganese.

The halogen hypothesis

Jeffrey Catalano is the corresponding author of the study. He is a professor of earth and planetary sciences at Washington University St. Louis and is also a faculty fellow at the McDonnell Center for the Space Sciences.

“The coupling between manganese oxides and oxygen suffers from a number of fundamental geochemical problems,” Catalano said in a press release. “Halogens occur on Mars in different forms than on Earth and in much larger amounts, and we guessed that they would be important for the fate of manganese,” Catalano said.

“One of the main differences between Earth and Mars is that Mars is rich in halogens, elements like chlorine and bromine. Mars is a halogen-rich planet, with bulk chlorine and bromine concentrations on Mars about four times greater than on Earth,” lead author Kaushik Mitra told Universe Today Chlorine and bromine are both halogens, and chlorate and bromate are the predominant forms of both on Mars.

Chlorate is a particularly powerful oxidizing agent. Could it have provided the oxygen needed to make the manganese oxides? There is a precedent in the way we treat our drinking water.

“We were inspired by reactions seen during chlorination of drinking water,” Catalano said. “Understanding other planets sometimes requires us to use knowledge from seemingly unrelated fields of science and engineering.”

“Untreated drinking water has contaminants, and so we ‘treat’ it before consumption,” said lead author Mitra. “There can be different types of contaminants: organic matter, microbes, metals (like lead), etc. Manganese can be one such contaminant,” explained Mitra.

Chemicals containing oxygenated chlorine (such as bleach) are routinely used to decontaminate water. But chlorine can also be a pollutant. How could introducing another contaminant end up decontamination of drinking water? “Use the metals,” said Mitra The universe today. “Chlorate is one such oxygenated chlorine compound that has the same properties as bleach. The contaminants (metal and oxygenated chlorine) will react together to produce products that can be filtered out or are harmless.”

This is where critical differences between Mars and Earth come into play. These differences undermine the tempting assumption that finding the same chemicals on Mars that formed on the oxygen-rich Earth necessarily means that ancient Mars was also oxygen-rich.

Not only are there far greater concentrations of both halogens on Mars, but the entire chemical environment is different. And chemical reactions are never just about the chemicals themselves. The environment in which the reactions take place dictates a lot about the reactions, and in this case the atmosphere and pH were different than on Earth. “Additionally, the atmosphere on early Mars was likely CO2-rich, which is also different from Earth,” Mitra said OUT. All that CO2 dictated the pH of the Martian water.

How they did it – The researchers conducted laboratory experiments with both chlorate and bromate to oxidize manganese samples in water. The water was made to reproduce the water on ancient Mars, which would have been mildly to slightly acidic with a pH between about 3.5 to 6.5 due to the CO2-rich atmosphere.

Their experiments showed that the rover-observed manganese oxides could not have been produced by an oxygen-rich atmosphere when temperature, pressure and pH were taken into account. It comes down to time scales. The manganese oxide layers the rovers found were very thick, suggesting a rapid build-up. If an oxygen-rich atmosphere was responsible for the manganese layers, the experiments show, they would be very thin, perhaps as thin as 20 nm.

“The rate of Mn(ii) oxidation by O2, both homogeneous and surface-catalyzed, is slower than by bromate,” the paper states. Mars’ low pH plays a decisive role in this. “As shown by the results, bromate can oxidize Mn(ii) down to pH~3 where Mn(ii) oxidation by O2 becomes about 108 × slower (100 × decrease in rate with each unit pH decrease.).”

The experiments also showed that while bromate was able to oxidize manganese at a rate that could explain the rover findings, chlorate was not. “Unlike bromate, chlorate produced no observable Mn(ii) oxidation in homogeneous systems in this study.” write the authors in their study.

A view from the Opportunity rover on Mars, which explored the rim of Endeavor crater in 2014. Image taken on Sol 3798 in October 2014, while the rover was en route to a small crater called Ulysses. The rover’s wheels knocked over some rocks as they crossed the rim of the crater, and these rocks contained manganese oxides.NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

“In our paper, we show that if oxygen were to produce the manganese oxide layers, then the oxide layers would have to be thin,” Mitra said The universe today. The rovers’ X-ray spectrometry found greater concentrations of manganese oxides than would be present in a nanometer-scale layer. “There are thus significant kinetic and thermodynamic barriers to O2 having acted as the oxidant that produced fracture-filling manganese oxide deposits on Mars.”

Since they are not that thin, there had to be another way they were oxidized. The experiments showed that Mars’ high concentration of bromate is responsible for creating manganese oxides.

“Oxidation does not require the involvement of oxygen by definition,” Mitra said. “Previously, we suggested viable oxidants on Mars, other than oxygen or via UV photooxidation, that help explain why the red planet is red. As for manganese, we just didn’t have a viable alternative to oxygen that could explain manganese oxides before now.”

Mars towards Earth

Mars is a puzzle we are only beginning to piece together, and we sometimes overlook the many fundamental differences between the two planets. It can be tempting to think of Mars as an “Earth gone wrong”. While Earth still has a magnetosphere, a rich atmosphere, and oceans, Mars may have had all of these until something went wrong and the planet became barren.

But as studies like this point out, there is a wide range of differences between Earth and Mars. “Although similar, there are significant differences between Earth and Mars, and that dictates the differences between the various aspects of the two planets (atmosphere, planetary structure, bulk planetary composition, crustal composition, hydrosphere, etc.),” ​​said Mitra .

Just because this study questions the existence of an oxygen-rich atmosphere doesn’t mean it rules out life on ancient Mars. After all, not all life forms on Earth need oxygen. In fact, when life first appeared on Earth, the atmosphere was not rich in oxygen. There are still simple forms of life that can do without.

“There are several life forms even on Earth that do not require oxygen to survive,” Mitra said. “I don’t see that as a ‘setback’ for habitability – just that there probably weren’t any oxygen-based life forms.”

On Earth, types of simple life forms called obligate anaerobes exist without oxygen and cannot actually survive in the presence of even low levels of molecular oxygen. And in 2010, scientists found three new complex multicellular life forms in the Mediterranean seabed that do not need oxygen. They spend their entire life cycle under permanently anoxic conditions. So there is precedent for life on early Mars even though it lacked an oxygen-rich atmosphere.

This study will not be the last word on Mars, manganese oxides and the planet’s ancient relationships. It’s just another important piece of the puzzle. In a decade or so, scientists will hopefully be in possession of a few additional pieces of the puzzle, perhaps the most important yet: the samples collected by the Perseverance rover in the Jezero crater.

“As of now, we have limited information on Martian rocks and minerals, including manganese oxides,” Mitra said The universe today. “We didn’t have mineralogical data from the manganese-rich sedimentary rocks.” Instead, the rovers provided elemental data, and scientists deduced the mineralogy from that.

“Having mineralogical and other microanalysis data (such as isotopic analysis) can provide so much more information,” Mitra explained in an email exchange. “Therefore, having the samples from Mars is crucial to understanding the chemical processes that occurred on the surface in the past, and will give us a much improved understanding of past geological, geochemical, environmental and habitable environments on Mars.”

This article was originally published on The universe today by EVAN GOUGH. Read the original article here.

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