Evidence of a Decreased Atmosphere on Ancient Mars has been Discovered by Planetary Scientists

Both Earth and Mars now have oxidizing atmospheres, which is why rust (a popular term for iron oxide) forms during the oxidation reaction of iron and oxygen in everyday life. For around two and a half billion years, the Earth’s atmosphere has been oxidizing, but before that, the planet’s atmosphere was reducing and there was no rust.

The Great Oxidation Event, or GOE, is the shift from a reduced world to an oxidized planet. This change was a crucial element of our planet’s development, and it was profoundly tied to the emergence of life here, notably the preponderance of oxygen-producing photosynthesis. Mars suffered its own major oxygenation event billions of years ago, according to planetary geologists at HKU. Before then, the red planet was not so red.

The discovery was recently reported in Nature Astronomy in an article co-authored by Jiacheng LIU, a research postgraduate student, and Associate Professor Dr. Joe MICHALSKI, both of whom are connected with the Research Division for Earth and Planetary Science and Laboratory for Space Research.

This is a rather remarkable study with findings that will significantly impact how we understand the early evolution of terrestrial planets and their surface environments.

Dr. Ryan McKenzie

In order to uncover the mineralogy and geochemistry of ancient rocks on Mars, the researchers employed infrared remote sensing and spectroscopy to quantify the molecular vibration of the material on the Martian surface from orbit.

View of Mars

The scientists demonstrated that ancient rocks on Mars exposed at the surface had been weathered under decreasing circumstances using comprehensive comparisons of infrared remote sensing data and data acquired in the laboratory here on Earth.

Many people are aware that Mars is currently frigid and dry, yet it was warmer and wetter 3.5 billion years ago. It was warm enough to allow for the production of river channels, lakes, and minerals created from water contact.

Scientists that utilized mathematical models to restrict the parameters of an early Martian atmosphere determined that greenhouse warming occurred, but they also concluded that the greenhouse must have included reduced gases rather than carbon dioxide, implying the presence of a reducing atmosphere. Yet, until today, there has been no proof that early Mars’ decreased atmosphere truly existed.

This study involves extensive infrared remote sensing of Mars, which entailed mapping minerals in exposed, worn rock units using infrared spectroscopy. The research was based on a thorough examination of weathered volcanic rocks on Hainan Island in southwestern China, where extensive basalt sequences resembling those seen on Mars may be found.

Jiacheng Liu used infrared spectroscopy in the lab to analyze the changed rocks in detail, and his findings were recently published in Applied Clay Science.

“Jiacheng has carried out a truly excellent Ph.D. project, built on careful analysis in the laboratory and application of those laboratory results to remote sensing of Mars,” Dr. Michalski commented, “Jiacheng has built on his detailed work on samples from Hainan Island to show that similar mineralogical trends occurred in rocks on Mars.”

Assistant Professor Dr. Ryan McKenzie from Research Division for Earth and Planetary Science is also impressed by these findings. “This is a rather remarkable study with findings that will significantly impact how we understand the early evolution of terrestrial planets and their surface environments. Because oxygen is a waste product of metabolic activities like photosynthesis, the change from a reducing to an oxidizing atmosphere on Earth 2.5 billion years ago was only conceivable because of the presence of life. We wouldn’t be here if bacteria didn’t produce oxygen, since it wouldn’t collect in our atmosphere. While there are certainly differences in the local conditions Mars and Earth have been subjected to during their evolutionary histories, my mind can’t help but start thinking about what Jiancheng’s results may mean for a potential early Martian biosphere,” Dr. McKenzie remarked.

Scientists are gearing up for an exciting year of Mars research and discovery as China’s first mission to Mars, Tianwen-1, has safely arrived in Mars orbit on February 10 and is scheduled to settle on Mars in May 2021. This study highlights how spectroscopy and remote sensing may lead to basic findings that are crucial to understanding Mars’ past.

Researchers are ready to immediately look for any evidence that life may have previously lived on ancient Mars as we begin to grasp the most ancient history of Mars, and HKU aims to be at the center of this major scientific adventure.