Evolution of river systems as plants colonized the land

The Paleozoic "greening" of the terrestrial surface as vascular plants colonized the landscape was among the most profound evolutionary changes in all of Earth history. Oceanic and atmospheric events during the early to mid Paleozoic have been widely linked to the spread of land vegetation, which decreased atmospheric CO2 , promoted global cooling, increased the runoff of nutrients to the oceans, and caused marine organisms to become extinct. Surprisingly, however, Paleozoic rivers barely feature in these discussions, even though early terrestrial plants colonized many river plains. Limited previous research suggests that, when river plains were unvegetated, channels inundated coastal areas with sand, but meandering rivers with muddy floodplains appeared in the Silurian as vegetation stabilized river banks. The present research programme aims to document river deposits through the crucial Cambrian to Devonian interval (540 to 360 million years ago), comparing the timing of events with what is known about the first appearances and abundance of early plants. Following a literature compilation, studies of river deposits and some of the world's earliest plant assemblages will be carried out at selected sites in North America and Europe. In younger Carboniferous rocks, we are studying the plants of river basins within mountain belts, in order to assess when plants spread into challenging inland areas: it seems, however, that they were there from the earliest days. We will also explore early evidence for wildfires, microbial contributions to river plains, and log jams that promoted channel switching once plants were sufficiently large and abundant.