ИСТИНА

Knowledge of the first ecosystems on land that existed outside aquatic environments has expanded significantly over the past decade (Stüeken et al., 2012; Beraldi-Campesi, 2013; Wellman and Strother, 2015; Lenton and Daines, 2017; Homann et al., 2018, 2019). Rapid increase in geochemical, paleontological, and paleogenetic data on terrestrial ecosystems of the Archean and Proterozoic opens up new possibilities for compiling still very crude models of soil diversity in the Precambrian. It can be assumed that ancient initial soils or proto-soils arose already at the very first stages of interaction between microorganisms and rocks. However, thick profiles of the Early Precambrian paleosols do not always allow to distinguish the first phases of soil formation. Soils formed under modern extreme conditions (Goryachkin et al., 2019) are the best available real-time models to approximate proto-soils that existed in various geological periods (Mitchell et al., 2021, 2023). Here we consider possible candidates for analogues of ancient proto-soils: • cryptic proto-soils with subsurface organic horizons. Soils with endolithic and hypolithic organic horizons of microbial origin (Mergelov et al., 2018, 2020) could be the first soils that developed in the absence of an ozone screen and under other extreme factors. The pore space inside the rocks or under their fragments created an ultraviolet shadow, retained moisture more efficiently and provided nutrients. Light still penetrated through translucent minerals like quartz or feldspars to a depth of ~1 cm allowing colonization by microbial autotrophs and formation of soil microprofiles in the pore space of weathered rocks. Over time, cryptic proto-soils could evolve into epilithic varieties, while eluvial-illuvial differentiation arose in cryptic proto-soils at later stages, when fungi and lichens appeared (~1.4-0.4 Ga). Now endolithic and hypolithic proto-soils are widely represented in polar regions, hot deserts and high mountains. • amphibious proto-soils of coastal shallow waters with alternating subaquatic/subaerial conditions are relatively well represented in geological record of the Precambrian due to the abundance of marginal continental landscapes at that time and rapid conservation by sedimentation. Amphibious proto-soils are usually represented by polyrhythmic sequences of microprofiles under microbial mats and are possibly associated with some of microbially induced sedimentary structures (MISS - Noffke, 2010). Amphibious proto-soils played an important role in sinking organic carbon in the Precambrian landscapes (now this C is partly preserved as kerogen). We discuss examples of fossil amphibious proto-soils in the volcanogenic-sedimentary sequences of the Kaapvaal, Pilbara and Karelian cratons. Their analogues are presented in modern coastal settings with microbial mats. • supraglacial proto-soils. Assemblages of mineral and organic components could have already been present on ice when subaerial surfaces massively turned into supraglacial during major cooling events in the Proterozoic. Paleoclimatic models show that even under conditions close to Snowball Earth, there was never a shortage of ice-free areas on the continents (Hoffman, 2016), and volcanic and continental dust accumulated on the ice. During periods of large-scale glaciations, supraglacial proto-soils were probably the most common soil-like bodies on the planet and served as refugiums for biota. On modern glaciers, supraglacial proto-soils develop on (a) cryoconite, (b) flat ice/snow surfaces, where algal and cyanobacterial biomass is partially transformed by heterotrophic communities into humic-like substances, and also under (c) metastable moss colonies (“glacier mice”) that grow on supraglacial sediments. • hydrothermal proto-soils were potentially widespread in the Early Precambrian due to the specifics of geological processes. The discovery of traces of microbial activity in geyserites aged 3.48 Ga (Djokic et al., 2017) stimulates the search for analogs of ancient hydrothermal proto-soils among the most extreme (microbial) variants of modern thermozems (Goldfarb, 2005) in regions of volcanic activity.