Humic substances in the early biosphere

Abstract

Humic substances and their organic-mineral compounds are the first stage in transformation of biotic residues into stable geopolymers, which comprise the main reservoir of organic C in the biosphere. Early appearance of HS in the Earth’s history is of principal importance for the understanding of geo-biological processes on land in the past. However, there is no fossil record of HS before land colonization by lignified vegetation (400 Ma). When the first soil HS were formed? Could HS be synthesized in the Precambrian before plants and mosses terrestrialization? The formation of HS occurs in mesophilic aerobic conditions and requires presence of oxidative catalysts and production of aromatic (phenolic) precursors by biota. In this paper, humification processes in algo-myco-bacterial and lichen communities are discussed from actualistic point of view. These communities are considered as a relict ecosystem, which could dominate on land during the Neoproterozoic-Early Paleozoic (1–0.5 Ga).