In this program we have played with iron , a fundamental component for our body that is responsible for transporting oxygen to the cells of our body, even if we only have about 4 grams. But that is not all. Iron has been and is closely linked to life.
The iron in our buildings and ships comes from a very remote time, between 3.5 and 2.5 billion years ago . So, the oxygen produced by the first photosynthetic bacteria did not end up in the atmosphere, but in the oceans. There it reacted with the large amounts of dissolved iron, forming enormous accumulations of iron oxide on the seabed : these are the so-called banded iron formations . It is in these places that we obtain the iron that we need to build and maintain our civilization.
Life in iron
To discover the oldest iron formations we must travel toIsua, in Greenland. In that frozen region we find the oldest evidence of the existence of free oxygen on Earth. And not only that. After chemically analyzing the rocks of Isua, an abnormal amount of carbon has been discovered. Carbon is the chemical element that serves as a framework to build living beings and for many the level of carbon in the rocks of Isua is proof that there was life, as well as oxygen, 3.8 billion years ago.
But we don’t have to go far to discover another peculiarity regarding iron. It is enough to approach theTinto river, in Huelva. In the 1980s, a European research project in biomining was launched to study the use ofleaching microorganisms to extract metals. Thus began the systematic study of the microbial ecology of the Tinto River. The idea of the scientists when they began to work was that the acidity of the waters -caused by sulfates- and its high iron content -which gives the river its color and its name- were due to the intense and uninterrupted mining exploitation for some time 5,000 years. It is not surprising: the Iberian Pyrite Belt, product of the clash of two continents, is one of the richest areas in metals in the world. What makes this area of Huelva a special place in the world is not the existence of acidic waters (the Phoenicians called the Urbero river, the one that burns) and its high concentration of heavy metals, essentially iron – up to 20 grams per liter -. What makes it unique is that they are100 kilometers of acidic waters. The atypical thing is the size.
The surprise that the river keeps inside was twofold. On the one hand, the “pollution” was not the product of industrial activity but of life itself. The second surprise was that in such an extreme environment there are not only the classic“comepiedras” bacteriaLeptospirillum spp., Acidithiobacillus ferrooxidansYAcidiphilium spp., which constitute only 1% of the river’s biological diversity. 65% of the river biomass is made up of aalgae fotosintética, something that nobody expected to find. These eukaryotic organisms (cells with nuclei) are also found in other close and neutral environments such as Guadiana or Guadalquivir. Why are they on the Rio Tinto? What advantage can living there have for your survival? Nobody knows, although it is thought that in the river there must be an appetizing component, iron. We must remember thatliving beings stick together by iron. Pathogens, for example, seek iron in our bodies.
We already have at stake the substratum of everything that happens in the river. ANDn the subsoil are large amounts of pirita, mineral composed mainly of sulfur and iron. Bacteria settled there 30 to 40 million years ago that do not need sunlight or feed on other organisms to obtain the energy necessary to live: theychemilotrophs, it is enough for them to oxidize inorganic compounds formed by sulfur and iron. Thus, when the iron in pyrite is oxidized by microorganisms,ferric ion that, when dissolved, gives the river its reddish color. As the atom is freed from the iron, thesulfurremains free and reacts with the oxygen in the air catalyzed by microorganisms, which acidifies the river. This has an amplifying effect, as acidic water makes it easier for iron to dissolve. We find a system governed by iron, in which while some microorganisms oxidize it, others reduce it. The cycle has remained like this for more than 30 million years, although possibly the metabolism that sustains it is one of the oldest on Earth.
In addition, the discovery of iron minerals, such asjarosite, on Mars has caused NASA to set its eyes on this protected natural landscape of the province of Huelva. Jarosite is an iron sulfate that is created under acidic conditions, which implies that the Tinto produces a mineralogy very similar to that of Mars.
