In the short BBC video Spain's otherworldly red river, Ricardo Amils, a researcher in Spain's Astrobiology Center says the following (amateur transcription):

Río Tinto is a peculiar place in our planet that has many similarities with Mars. The most important one is iron. Mars is red because of its iron, and Río Tinto is the red river.

The river’s singular red colour comes from ferric ion, iron oxidised due to the river’s acidity...

Considering the similar geochemistry and minerology, this place is a good analogue to Mars. Life on Mars would probably look like life here.

During his trips to South America, Charles Darwin found life in extreme saline conditions. He then predicted that we would find life in the subsoil. It took us 200 years to prove him right. If there is life on Mars, as some of us believe, it has to be in the subsoil.

What definitely equialised Río Tinto and Mars was the discovery of jarosite in Mars. This iron and potassium sulphate is produced in great quantities in Río Tinto.

Upon drilling the river’s subsoil, scientists found a great variety of bacteria and microorganisms. These could thrive in extreme conditions, and need no oxygen.

Question: Is it possible to better explain the connection (if any) between jarosite and subsoil biological activity that's hinted at by the video?

The BBC's news videos don't always remain viewable indefinitely, so here are some screen shots for background and context. click for full size

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    $\begingroup$ Just a tip. I have been there with university and the romans extracted the jarosite level. It is or it was an Ag rich jarosite. My teacher said he found amazing romans knew were the Ag was centuries before Lavoisier was born! $\endgroup$
    – user18590
    Mar 6 '20 at 7:12
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    $\begingroup$ @Universal_learner oh how cool, and yes I find that quite amazing as well. That's something to think (and maybe ask) about, hmm.... $\endgroup$
    – uhoh
    Mar 6 '20 at 10:17
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    $\begingroup$ An interesting section about Jarosite, with reference to Mars. This mineral could only have precipitated from highly acidic water. Any sea at Meridiani was more like battery acid than drinking water. Given the abundance of basaltic lavas on the Martian surface, it is surprising that these waters would be so acidic. Reactions between water and basalt on the Earth tend to produce neutral to basic solutions. $\endgroup$
    – Fred
    Mar 7 '20 at 2:42
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    $\begingroup$ Another interesting section about biogenic jarosite. **... a strain of the fungus Purpureocillium lilacinum from the acidic environment of Río Tinto. An indepth study of its biomineralization abilities revealed that this fungus was able to produce biogenic jarosite ... The biomineralization process started in both cases in the cell wall, at the outer part of the fungal cell. However, living and dead fungal biomass performed differently in terms of biomineralization efficiency ... ** $\endgroup$
    – Fred
    Mar 7 '20 at 3:00
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    $\begingroup$ ...The authors explain this difference by the presence of EPS associated with living fungal biomass. They conclude that jarosite formation is a process independent from active metabolism and that requires fungal biomass and EPS as nucleation sites.. I'm assuming EPS is Extracellular Protein Secretion. $\endgroup$
    – Fred
    Mar 7 '20 at 3:01

From what I've read so far, it appears jarosite may not be a prerequisite for the formation of certain life forms, instead that it is produced by certain organisms.

Río Tinto (Huelva, southwestern Spain) is an extreme environment with a remarkably constant acidic pH and a high concentration of heavy metals, conditions generated by the metabolic activity of chemolithotrophic microorganisms thriving in the rich complex sulfides of the Iberian Pyrite Belt (IPB). Fungal strains isolated from the Tinto basin were characterized morphologically and phylogenetically. The strain identified as Purpureocillium lilacinum specifically induced the formation of a yellow-ocher precipitate, identified as hydronium-jarosite, an iron sulfate mineral which appears in abundance on the banks of Río Tinto. The biomineral was characterized by X-ray diffraction (XRD) and its formation was observed with high-resolution transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled to energy-dispersive X-ray spectroscopy (EDX) microanalysis. Jarosite began to nucleate on the fungal cell wall, associated to the EPS, due to a local increase in the Fe(3+) /Fe(2+) ratio which generated supersaturation. Its formation has been also observed in non-viable cells, although with much less efficiency. The occurrence of P. lilacinum in an ecosystem with high concentrations of ferric iron and sulfates such as Río Tinto suggests that it could participate in the process of jarosite precipitation, helping to shape and control the geochemical properties of this environment.

Another reference, states that

But there is something else about jarosite that makes it interesting. One of the steps in its formation involves combining pyrite (ferrous sulfide) with oxygen. This oxidation reaction can be performed by certain "rock-eating" microorganisms.

... And yet, there remains the tantalizing possibility that martian jarosite owes its existence to the martian version of rock-eating microbes. If so, remnants of these organisms may be locked in the mineral.

... This is because jarosite on Earth is known to let all sorts of foreign elements incorporate into its crystal structure.


amino acids, the basic components of proteins

Fate of Lipid Biosignatures in a Mars-Analogue Sulfur Stream

Formation of Rubidium Jarosite During the Microbiological Oxidation of Ferrous Iron at Room Temperature

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    $\begingroup$ Oh this turns out to be really interesting! $\endgroup$
    – uhoh
    Mar 7 '20 at 4:22

Jarosite is formed from iron ore deposits by the oxidation of iron sulphides. It has nothing to do with the presence of life, but it forms an extreme environment that can only be tolerated by extremophiles. That is the only connection jarosite has with biological activity. The discovery of jarosite on Mars does not mean that there are likely to be microbes of any kind associated with it.

Extremophiles are microbes which enjoy extreme environments: extremely cold, extremely hot, extremely acid, extremely salty, extremely radioactive and so on. Most of them don't need oxygen and many metabolise sulphur to make a living. Some like the dark ocean depths and pressures in the vicinity of black smokers (deep sea fumaroles).

Some extremophiles are methanogens, that is to say their metabolism generates methane, which is why the detection of short-lived methane emissions on Mars attracted a lot of interest. A common methanogen on Earth lives in anoxic marshes, usually in woodland, where it generates marsh gas (methane). Microbes are ubiquitous on Earth, you can't get away from them. They are even found in rocks hundreds of metres below the surface.

Today you can't really find Mars-like conditions on Earth. The two atmospheres are very different in composition, the pressure is very different, average temperatures on Mars are far colder, but four billion years ago Earth and Mars were very similar. Both had seas, a dense atmosphere composed mainly of CO2, and Mars was a lot warmer, but we don't know for sure whether life was spontaneously generated there as it was here on Earth. Probably it wasn't.

These Earth-like conditions on Mars vanished within a billion years or so, and any possibility of spontaneous generation of life from inert materials vanished with them. Meanwhile Earth's atmosphere has been greatly modified by biological activity, while that of Mars has stayed much the same except for a reduction in pressure caused by losses into space and the freezing out of some CO2 at the poles, mainly the south pole.

  • $\begingroup$ I think it's the subsoil environments that are being compared, specifically locations on Earth where there is little or no oxygen. "Upon drilling the river’s subsoil, scientists found a great variety of bacteria and microorganisms. These could thrive in extreme conditions, and need no oxygen." $\endgroup$
    – uhoh
    Mar 6 '20 at 0:11
  • $\begingroup$ Perhaps I should have made it clearer that the microbes I refer to are mainly found in the subsoil, as they don't like oxygen. It seems obvious to me, I thought everyone knew. The environments I describe are not usually found on the surface. When I say hot, I mean really hot, 80C or more. Some of these microbes generate methane. On Earth the subsoil is full of bacteria, and they can be found quite deep In the crust. $\endgroup$ Mar 6 '20 at 8:16
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    $\begingroup$ Michael focus on answering the question. You look again to throw what you know about the topics mentioned not answering again. About sources, it is a lost battle. It looks you don't want to source. We are throwing this po-up, needs sources $\endgroup$
    – user18590
    Mar 6 '20 at 14:47
  • $\begingroup$ My first sentence answers it. but the main thrust of the question is about whether it makes life more likely on Mars. I answer that too. $\endgroup$ Mar 6 '20 at 14:59
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    $\begingroup$ Hi MichaelWalsby can you make an edit to your answer and adjust it a bit in response to the comments? I see that you've responded in comments, but votes apply to the post itself. Once you edit, Stack Exchange allows people to change their votes! $\endgroup$
    – uhoh
    Mar 7 '20 at 3:24

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