Sampriti Roy, University of Calcutta
The Earth currently has an oxidizing atmosphere. An oxidizing atmosphere is essentially an atmosphere that is rich in oxygen and is responsible for the rust that will develop on an iron-rich object in your home if it’s released into the air for a critical amount of time. Though this is the observation now, this was not the case about roughly 2.5 billion years ago. Back then, the Earth had a reducing atmosphere. Recently, it has been found that Earth shares this atmospheric characteristic and change with another planet- Mars.
The Great Oxidation Event (GOE)
The transition of the Earth’s atmosphere from a reducing to an oxidizing one is termed the Great Oxidation Event. It is a process that played a crucial part in the evolution of living beings on Earth. According to Ariel Anbar, an Arizona State geochemist, “The GOE is probably the most fundamental transformation in the history of the planet, aside from the origin of life itself.” Recently, planetary geologists at the University of Hong Kong have found out that Mars went through such a fundamental transformation of its own in its atmospheric nature billions of years ago.
it is known to many that the Martian atmosphere is not exactly what we would consider ‘habitable’ due to dryness and cold weather among other conditions, but the same wasn’t the case 3.5 billion years ago. During that time, it is said to have been wetter and warmer- enough to allow the formation of lakes, minerals and river channels. Scientists have used mathematical models to establish that global warming did indeed occur at a certain period and that a reducing atmosphere may have existed. But there was no concrete evidence to prove the fact. This however changes with the recent research done at the University of Hong Kong.
Through a paper published in Nature Astronomy, Jiacheng Liu and his advisor Joe Michalski from the University of Hong Kong’s Research Division for Earth and Planetary Science and Laboratory for Space Research have put forward the evidence that there did exist a reducing atmosphere on Mars.
How did they find the proof of a reducing atmosphere?
•Data collection from Mars: To reveal and study the geochemistry and mineralogy of ancient Martian rocks, the researchers used spectroscopy and remote sensing to measure molecular vibrations of the material on the Martian Surface from orbit.
•Data collection from Earth for comparison: Weathered volcanic rocks in the Hainan Island in southwestern China were analysed. This location was selected as the thick sequences of basalt here resemble the volcanic rocks found on Mars. Infrared spectroscopy was used to map the minerals in rock units that were exposed and weathered.
By comparing the data collected in the laboratory here on Earth and data collected by remote sensing from Mars, the team was able to show that the exposed ancient Martian rocks (on the surface) had been weathered under a reducing condition.
It was reported by the team that there had been a widespread, strong loss of iron in chemically weathered bedrock sections in the Mawrth Vallis region as well as other 3–4-billion-year-old terrains on Mars. When the Martian data and Earth laboratory data were compared, the separation of Fe from Al in Martian palaeosols appear similar to the trends observed in palaeosols on Earth before the Great Oxidation Event (GOE).
This finding, alongside providing evidence of a reducing atmosphere, also shows us what an important part remote sensing and spectroscopy plays in understanding Martian history.
How is this study significant in the future study of evolution and the environment?
The study is being called a milestone in the research of terrestrial planets. As stated by Dr Ryan Mckenzie (University of Hong Kong), the study is “remarkable” and consists of findings that are sure to impact the way we perceive surface environments of terrestrial planets and their early evolutionary events.
With China’s first mission to Mars “Tianwen-1” underway right now and set to land on Mars in May 2021, researchers are preparing for an exciting year in the discovery and exploration of Mars. The University of Hong Kong plans to play a central role in this great scientific adventure that could answer important questions regarding evolution, the Martian environment and the search for something that has often been speculated to have existed on Mars- life.
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Source: “Anoxic chemical weathering under a reducing greenhouse on early Mars” by J. Liu, J. R. Michalski, W. Tan, H. He, B. Ye and L. Xiao, 11 February 2021, Nature Astronomy.DOI: 10.1038/s41550-021-01303-5
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