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Harvard researchers published a revised model of the early Martian environment that could explain how life may have emerged on Mars in Nature Geoscience earlier this month.
The Harvard-led research team — in collaboration with Brown University, California Institute of Technology, Stony Brook University, and NASA — proposed that Mars once boasted a dynamic environment characterized by long cold periods interspersed with episodes of warmth.
Today, 3.5 billion years later, Mars is known to be very cold and dry. Its desolate environment is inhospitable to life: liquid water is nearly, if not wholly, nonexistent, and the oxygen-rich atmosphere that gives the planet its familiar reddish tinge is hostile to the early biosynthesis required for life — historically thought to be only possible in oxygen-poor atmospheres.
Over the years, though, NASA rovers have found geological evidence that points toward the past presence of flowing liquid water and minerals that form only in oxygen-poor environments, suggesting that the planet once had conditions to support early life.
The researchers modeled Mars’ climate and atmospheric chemistry, actually finding “fluctuations” between these oxygen-poor — or reducing — and oxygen-rich — or oxidizing — conditions over time, according to Robin D. Wordsworth, lead author and Harvard professor of Environmental Science and Engineering.
The fluctuating presence or absence of oxygen on Mars would have affected its climate over time, according to Wordsworth. Because oxygen is a poor greenhouse gas, the Martian atmosphere would have trapped less heat during its oxygen-rich periods. Oxygen-poor periods, however, were characterized by a greater abundance of hydrogen gas, which — in combination with carbon dioxide — would have acted as a “potent” greenhouse gas and more efficiently retained heat.
“There is a current popular hypothesis for warming early Mars in a reducing environment with a lot of hydrogen. This paper suggests that the early Martian climate didn’t need to be primarily oxidizing or reducing; that oscillating between these environments is possible,” Kathryn E. Steakley, NASA postdoctoral program fellow and contributor to the paper, wrote in an emailed statement.
“We don’t know if life ever emerged on Mars,” Wordsworth said. “But what our model does show, if this scenario is correct, is that you have episodic periods where the surface is warm, and the chemistry is conducive to early forms of life — but then long periods where the surface is cold and oxidizing.”
Because fluctuations back to an biochemically hostile, oxygen-rich atmosphere would have been harmful to early developing life forms, Wordsworth said that “if life did emerge, it would have best survived in the subsurface of Mars rather than continuously on the surface.”
The next steps for the team include testing their model with data collected by NASA’s Perseverance rover — which landed in the Jezero Crater of the red planet last month. They will examine both materials on site and rock samples sent back to Earth via a rover provided by the European Space Agency, with a current launch date of 2026.
“It’s an incredibly ambitious mission — the most complicated thing that NASA and ESA have tried to do together, with the possible exception of the Apollo missions,” Wordsworth said. “Science-wise, it’s going to be phenomenal. It’s just going to revolutionize our understanding of the Martian surface.”
—Staff writer Justin Lee can be reached at email@example.com.
—Staff writer Lauren L. Zhang can be reached at firstname.lastname@example.org.
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