The search for life on Mars continues, but a new study suggests taking a different approach. While many previous efforts to find life on the Red Planet have focused on dried lake bed environments, where sediments were deposited by water billions of years ago, it's possible that life never made it to these surface regions even if it did exist on Mars.

A new study published December 18 in Nature Geoscience encourages researchers to instead search areas on Mars that could have supported hydrothermal activity in the ancient past. Digging into the rock to search for fossils around these locations, where hot water and nutrients would have been flowing from vents on Mars' ancient ocean floor, could be the best bet to find evidence of past life on Mars.

Self-portrait of NASA’s Curiosity Mars rover at the Quela drilling location in the Murray Buttes area on lower Mount Sharp. NASA/JPL-Caltech/MSSS

While dried lake beds on Earth contain a multitude of evidence of diverse life, the researchers caution that this may not be the case on Mars. The study points out that abundant surface life on Earth was only possible after cyanobacteria evolved to engage in oxygen-producing photosynthesis, about 1.5 billion years after the first life formed on Earth, which was roughly 4 billion years ago. This new source of oxygen created the ozone layer, buffering the planet from ultraviolet radiation and solar winds.



"On Earth, surface sedimentary environments are thought to best preserve evidence of ancient life, but this is mostly because our planet has been dominated by high photosynthetic biomass production at the surface for the last ~2,500 million years or more," reads the study. "By the time oxygenic photosynthesis evolved on Earth, Mars had been a hyperarid, frozen desert with a surface bombarded by high-energy solar and cosmic radiation for more than a billion years, and as a result, photosynthetic surface life may never have occurred on Mars. Therefore, one must question whether searching for evidence of life in Martian surface sediments is the best strategy."

Many scientists who study the origins of life on Earth, or abiogenesis, believe that the first organisms could have evolved around warm, nutrient-rich hydrothermal vents on the seafloor. Surface life only took hold after photosynthesis generated the protective ozone layer. Mars, however, which is about 10 times less massive than Earth, cooled in its interior and lost the magnetic field that protected its atmosphere from space weather. As a result, roughly 3.7 billion years ago, Mars lost almost all of its atmosphere and turned into the frigid desert we find today.

Therefore, for surface life to have thrived on Mars, photosynthesis would have needed to develop on the Red Planet before Earth, an unlikely scenario. Alternatively, the study authors propose seeking out locations where hydrothermal activity was once present on Mars and searching underground for fossils.

Bright, silica-rich minerals accidentally uncovered by NASA’s Spirit rover when the rover’s jammed wheel dragged across the sand and exposed the material in May 2007. The composition of the minerals suggests they formed in a wet area with hydrothermal activity in Mars’ ancient past. NASA/JPL-Caltech/Cornell

There is significant evidence that these concentrations of hydrothermal activity did exist at one point on ancient Mars. Hydrated silicate minerals have been spotted in abundance by infrared scans of the planet, and while some of these may have formed on the surface during dramatic climate swings, "many of the deposits represent materials that were seemingly exhumed from the subsurface," reads the study. In addition, the Spirit rover accidentally uncovered nearly pure opaline silica in Gusev crater in 2007, strong evidence of active hydrothermal processes in the past.

Those who hope to search these silica deposits for signs of life on Mars might not have to wait long. Jack Mustard, a geology professor at Brown University and co-author of the new study, told Space.com that he hopes the upcoming Mars 2020 rover will be used to investigate "mineralized fracture zones."



"These would be places where there was fluid flow in the crust, and where you get mixing between different fluids from different sources that have potentially different concentrations of important elements, as well as dissolved hydrogen," Mustard told Space.com. "Those would be cool."

Finding evidence of life around a once-active hydrothermal area on Mars would be a two-fold breakthrough in science. In addition to confirming that life has existed on other planets, it would provide strong evidence that hydrothermal vents are indeed the cradle of life on Earth. We may not find a Martian fossil around these hydrothermal areas, but with the evidence we have, it seems crazy not to look.

h/t Space.com

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