Abstract
From Humboldt is particularly interesting -and little know- his description of mineral coatings on rocks 200 years ago, reported in his book Personal Narrative of Travels to the Equinoctial Regions of the New Continent during the years 1799-1804, co-written with Aimé Bonpland, for which is considerate the father of rock coating research. On June 5th 1799 set sail from A Coruña -Spain- to Cumaná -Venezuela- beginning five years of expedition. While they explored the Orinoco River system, in th eriver basin waterfalls, Humboldt observed the presence of dark coating depositions. He ascertained a manganese-rich accretion, reporting similar structures in other places. Nowadays, these types of geochemical coatings are called rock varnish -or desert varnish in arid environments- in scientific literature. Composed by clay minerals -Si, Al- cemented on a bedrock with variable manganese [Mn]-iron[Fe]oxides and trace elements in it smatrix, only has been studied in detail just during the last decades, achieving an accurate chemical and microbiological description. These structures have great geomicroecological interest because (i) it has a high oxidative power, (ii) gather polyextreme conditions, (iii) stressful conditions, (iv) host microorganisms of biotechnological interest and (v) can preserve interesting biomarkers embedded in its matrix. In fact, interesting rock varnish-like structures have been observed in Mars where appreciable amounts of manganese have been detected by Chem-Cam onboard Curiosity rover. Therefore, the study of rock varnishes, which legacy was initiated by Humboldt, can be considered as another terrestrial analogue and to be explored much deeper.
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The Astrobiological figure of Humboldt as pioneer in the rock varnish research
From Humboldt is particularly interesting -and little know- his description of mineral coatings on rocks 200 years ago, reported in his book Personal Narrative of Travels to the Equinoctial Regions of the New Continent during the years 1799-1804, co-written with Aimé Bonpland, for which is considerate the father of rock coating research. On June 5th 1799 set sail from A Coruña -Spain- to Cumaná -Venezuela- beginning five years of expedition. While they explored the Orinoco River system, in th eriver basin waterfalls, Humboldt observed the presence of dark coating depositions. He ascertained a manganese-rich accretion, reporting similar structures in other places. Nowadays, these types of geochemical coatings are called rock varnish -or desert varnish in arid environments- in scientific literature. Composed by clay minerals -Si, Al- cemented on a bedrock with variable manganese [Mn]-iron[Fe]oxides and trace elements in it smatrix, only has been studied in detail just during the last decades, achieving an accurate chemical and microbiological description. These structures have great geomicroecological interest because (i) it has a high oxidative power, (ii) gather polyextreme conditions, (iii) stressful conditions, (iv) host microorganisms of biotechnological interest and (v) can preserve interesting biomarkers embedded in its matrix. In fact, interesting rock varnish-like structures have been observed in Mars where appreciable amounts of manganese have been detected by Chem-Cam onboard Curiosity rover. Therefore, the study of rock varnishes, which legacy was initiated by Humboldt, can be considered as another terrestrial analogue and to be explored much deeper.