A baptism by fire: fossil charcoal from eastern Euramerica reveals the earliest (Homerian) terrestrial biota evolved in a flammable world

Abstract

Charred fossils from the Wenlock (Wales) and Ludlow (Poland) are evidence of the earliest wildfires to date, showing that this phenomenon was contemporaneous with the earliest records of land plant macrofossils. These data indicate that fires began to influence Earth system processes alongside those wrought by the advent of an embryophytic terrestrial flora. By the mid-Silurian, fires affected atmospheric composition, sedimentary systems, carbon and nutrient cycling, landscape diversity, community composition and species interactions. As global heating alters wildfire regimes, greater recognition is being given to fires and their ecosystem impacts, a relationship we now know extends back >430 myr. Here we document the taxonomic composition of charred phytoclasts, evidence of wildfire activity, from two discrete Silurian localities: the Pen-y-lan Mudstone, Rumney, Wales, and the Winnica Formation, Holy Cross Mountains, Poland. Nematophytes dominate each mesofossil assemblage and quantitative reflectance data indicate generally low-temperature fires at both sites, but with locally intense conditions. These and other Silurian assemblages, herein documented as bearing charcoal, are used to evaluate the systematics, fuel load and burn temperatures of these earliest wildfires. We propose a diagrammatic reconstruction to explain the seeming disparity between the diminutive size of the embryophytic biota and the highest temperatures (>700°C) recorded in these charcoals. Supplementary material : Raw mean random reflectance ( R o %) data from Rumney Borehole, Winnica, Ludford Lane and North Brown Clee Hill, sorted by both locality and morphotype, are available at https://doi.org/10.6084/m9.figshare.c.6179309