Decoding the Deep-Time Rhizosphere: A Rhizolith-Centric Perspective on Root Evolution as a Planetary Engine

Root systems, the hidden half of terrestrial plants, have been a fundamental geological agent since the late Early Paleozoic, with their evolution preserved in a rich but underutilized archive of soils and sediments. This review adopts a rhizolith-centric perspective to trace the co-evolution of root systems and the Earth’s surface environment from the Silurian to the present. Two profound, linked transitions are recognized. The first is the Devonian “Rooting Revolution,” during which true roots and their mycorrhizal partners scaled up silicate weathering, drawing down atmospheric CO2 and contributing to the initiation of the Late Paleozoic Ice Age. The second is the Mesozoic–Cenozoic “Rhizosphere Expansion,” led by angiosperms, which greatly amplified the existing weathering engine through higher transpiration, denser fibrous roots, and more diverse rhizosphere microbial and mycorrhizal communities. Reading rhizoliths through their morphology, mineralogy, and isotopic signatures makes it possible to reconstruct how roots became central regulators of long-term carbon and phosphorus cycling, builders of the pedosphere, and stabilizers of landscapes. Beyond these geochemical roles, this also integrates the dimension of roots as a persistent nutritional resource for terrestrial vertebrates—from Early Permian stem amniotes and early synapsids and reptiles to Pleistocene megafauna and early hominins. By synthesizing evidence from paleontology, sedimentology, geochemistry, and vertebrate paleoecology, this review offers a rhizolith-centric framework—anchored by the two linked transitions described above—for refining Earth system models and for understanding the feedbacks between root evolution and global environmental change.