Does the Measured Abundance Suggest a Biological Origin for the Ancient Alkanes Preserved in a Martian Mudstone?

Does the Measured Abundance Suggest a Biological Origin for the Ancient Alkanes Preserved in a Martian Mudstone?
Alexander A. Pavlov, Caroline Freissinet, Daniel P. Glavin, Christopher H. House, Jennifer C. Stern, Amy C. McAdam, Anais Roussel, Jason P. Dworkin, Luoth Chou, Andrew Steele, Paul R. Mahaffy, Denise Buckner, Felipe Gomez
Astrobiology, vol 26, no. 2, February, 2026

The 1964 Mariner Mars flyby put to rest all, and I mean every single one, of the sci fi tropes about canals and Martians with large heads wearing metallic gowns. Those were all a Mars that never was. NASA’s Mars rovers are bringing a real, more interesting Martian geology and possibly paleontology into focus.

First mudstone, a rock whose precursors need lots of water to form, on Mars, the dusty, dry, Red Planet. When I was a kid, it was unthinkable that a nuclear powered robot would find incontrovertible evidence of water, lots of water, on Mars. That would have been science fiction.

Second, sedimentary rock with carbon molecules in it, organic carbon molecules, alkanes, like methane, ethane, propane and butane, on Mars. Also unthinkable even 30 years ago. This paper references yet another paper that used the Potassium-Argon dating method to put the age of the mudstone at 4.21 ± 0.35 billion years.

Other isotope ratio tests show that the mudstone has been exposed on the Martian surface for about 80 million years. That means the mudstone has been sitting out in the open since the Campanian stage of late Cretaceous. Dinosaurs walked the earth, and Plesiosaurs were in the oceans when “recent exposure by wind-driven scarp retreat” occurred.

The fact of the matter is that cosmic rays and other radiation break up organic molecules. The authors of this paper estimate the original amount of alkanes in the rock by looking at various radiolysis experiments. They have to take care since Martian conditions aren’t exactly well known, and none of the experiments exactly matched the mudstone, its temperature and pressure. Nevertheless, the mudstone must have had a decent amount of organic molecules in it 4.21 ± 0.35 billion years ago.

At that point, the question becomes “how would this amount of organics get into the original mud?”, and the paper switches to analyzing ways that could happen.

The authors discard carbonaceous meteorites, interplanetary dust particles, photochemically produced organic atmospheric haze, and serpentinization. They leave themselves two suggestions, organic molecules produced from high temperature and pressure caused by nearby meteor impacts into water and carbonate rocks, and leftovers from a hypothetical Martian biosphere.

The authors are super cautious about the Martian biosphere suggestion. Given the weird media splash that the ALH 84001 meteorite made, I expect they’re trying as hard as possible to quell media uninformed speculation.

The mudstone’s date puts its formation in the Martian Noachian period 4.1 - 3.7 billion years ago. That’s about the age estimated for the Last Universal Common Ancestor of Earth’s biosphere. People argue about whether carbon isotope ratios indicate life or not on Earth in rocks of that age. The authors make the cliche “more research is needed”, but in this case, I think they’re justified.

Bonus Conspiracy Theory Section

How many soft reveals of Martian life do we get? First, it was the weird results from the 1976 Viking lander experiments, then the ALH 84001 meteorite the seasonal methane in Mars’ atmosphere, then discovery of clear evidence of plenty of water by Spirit and Opportunity rovers. Now, we get Curiosity and Perseverance rovers finding mudstone (!!!) in Jezero and Gale craters, along with some chemical evidence that could easily be interpreted as the remains of ancient life.