Biotic-abiotic mingle in rock varnish formation: A new perspective

Rocks in arid to semi-arid regions all over the world have a naturally occurring coating called "rock varnish" or "desert varnish" on their surface. These lustrous, black-to-brown mesoscopic coatings on rocks have long piqued the interest of scholars from a wide range of disciplines. However, there are gaps in our understanding, particularly in relation to the formation of rock varnish. Rock varnish development is supported by competing evidence from the biotic and abiotic schools of thought. In the current investigation, we advance and support a previous polygenetic model by proposing that biotic and abiotic factors collaborate to form these microscopic coatings on the rock surfaces. Physicochemical evidences in this work points toward a new perspective, citing an initial abiotic triggering event followed by biotic processes.