Unraveling the age-old enigma regarding the pictorial rock landscape of the desert
In a groundbreaking discovery, a team of scientists, led by Usha F. Lingappa, a graduate student at Caltech, have proposed that rock varnish, a dark-stained substance found on rocks in deserts, is formed by microbial communities. The study, which was supported by the National Science Foundation, the National Institutes of Health, and the National Aeronautics and Space Administration, was published in the Proceedings of the National Academy of Sciences on 22 June 2021.
Rock varnish is unusually rich in manganese, and among the team's key observations was that manganese in desert dust is usually in particle form, but it is deposited in more continuous layers in varnish. X-ray spectroscopy methods at the Stanford Synchrotron Radiation Lightsource (SSRL), a DOE Office of Science user facility, revealed this fact and showed that the kinds of manganese compounds in varnish were the result of ongoing chemical cycles, rather than being left out in the sun for millennia.
The manganese project arrived at an opportune time due to recent advancements in X-ray spectroscopy at SSRL. Improvements in X-ray beam size provided a finer-grained picture of rock varnish, according to Webb, a researcher involved in the study. Other advancements in X-ray technology reduced the risk of damaging the research samples.
The team used various techniques, including DNA sequencing, mineralogical analyses, electron microscopy, and X-ray spectroscopy, to study the desert ecosystem and rock varnish. Among the microbes they discovered were bacteria called Chroococcidiopsis, which are known to use manganese to combat the oxidative effects of the harsh desert sun.
According to the study, these microbial communities use manganese to defend against the punishing desert sun. The prevalence of these bacteria, combined with the observed chemical cycles, led Lingappa and her team to conclude that rock varnish was left behind by these bacteria.
Webb expressed enthusiasm for the manganese project, stating he has been a "mangaphile" for some time. The DOI for the study is 10.1073/pnas.2025188118. The authentic authors of the study are primarily affiliated with institutions in the United States.
