When I started my investigation into the mechanism of planetary formation, everybody believed that Mars started out with an oxidized atmosphere, that is the volcanoes that emitted the atmosphere emitted carbon dioxide, as most Earth volcanoes do today. I disagreed, for two main reasons. The first was it was difficult to see how carbon dioxide could be accreted underground, and the second was it was difficult to see how the early Martian rivers flowed. The usual answer was there was a massive greenhouse effect from 10 bars of CO2, but the remains of this steadfastly refused to be found. Had there been, there should be massive lime deposits on Mars, and while such lime does occur, it is only in relatively trivial amounts. A second reason was such an atmosphere should have so much pressure it would rain out in the Martian winter.

I proposed that the early atmosphere of Mars was reducing, which meant that carbon was represented by methane, and nitrogen by ammonia. The ammonia would permit water flow because it dissolves in ice and flows down to minus 80 degrees C Further evidence from inclusions in ancient rocks was that the ancient atmosphere of Earth was rich in methane and the seawater in ammonia. These were important because as the methane became oxidised by reaction with water and UV light, we started to form the molecules so important for the generation of life. Thus methane can be first oxidised to formaldehyde, which can then condense to form carbohydrates.

Anyway, it now appears that my picture is starting to get acknowledged, even if I am not. In a recent Nature communications (2024, 15: 5648) we read “early Mars was characterized by icy highlands, episodic warmth and reducing atmosphere.”

So what did they find? They looked at the distribution of the low surface iron abundance in the ancient terrains and showed that iron abundance decreases with elevation in the older Noachian terrains and with latitude in the younger ones. The Noachian period on Mars was about 4.1 to 3.7 billion years ago. The authors suggest the low temperatures contributed here, probably due to freeze thaw cycles breaking up rocks, then they suggest that the distribution mode switched from elevation dependent to latitude dependent. Why that would happen is fairly simple. The initial atmosphere would be highly reducing but oxidation due to solar energy would gradually reduce the greenhouse effect and the concentration of leaching chemicals, and the effect would become more pronounced where it was warmer. The authors conclude that such gradual oxidation gradually cooled Mars and led it to where it is today.

One interesting point is that rovers have found significant levels of sulphate, so could sulphuric acid have been responsible for this iron leaching? They produce a map of Mars that highlights the places where weathering occurred, where sulphates occurred and where the iron depletion occurred. A casual glance shows the sulphates could not have been responsible as they are not in the right places.

However, I disagree with the authors on one point. They argue that the leaching was due to water becoming acidic when at low temperatures. Sorry, no, because the only way you get liquid at those temperatures is from the presence of ammonia, and that is basic. Ammonia by itself will not attack iron oxides, but it should have other chemical species with it. More work is required to understand exactly what went on there.

This will be my last post this year, so may I wish you all a merry Christmas. It is also possible it will be my last post. Chemotherapy has brewed up aggressive chemo-resistant tumours, and I may be too weak, or not here, next year to write. We shall see.