Abstract

14 Bare rock surfaces in dry to semi-arid places of the world usually have a black-brown, 15 metallic sheen covering known as "rock/desert varnish." Rock varnishes are naturally 16 occurring surface textures rich in Mn and Fe that are deposited on rocks. The varnish surface 17 looks to be an ideal environment for microbial development. The function of bacteria in 18 varnish formation, on the other hand, is currently being debated. Therefore, researchers 19 throughout the world have long been interested in the biogeochemical fingerprints of life in 20 severe settings, and the identification of organic entities is an important aspect of the quest 21 for early life in extreme circumstances. High-altitude Ladakh, one of the world's harshest dry 22 deserts, was chosen as the study's sample location due to its severe climatic circumstances. 23 The current study illustrates significant microbial fingerprinting using organic biomarkers 24 and isotopic analyses in conjunction with electron microscopy, revealing the presence of 25 organic metabolites such as fatty acids, alkyl benzenes, oxime, amide, and fatty acids on the 26 varnish layer as a result of mineral-microbial interactions. We propose for the first time that 27 how change in surface wettability characteristics from hydrophilic (in host rock) to 28 hydrophobic (in varnish) allowed microbial life to thrive in extreme environments. The 29 current work provides evidence for a long-standing question about microbial affinity for the 30 varnish layer and illustrates the significance of hydrophobicity in the varnish layer as a 31 crucial component for understanding biogeochemical processes related to varnish growth. 32