Evolution of river systems as plants colonized the land

古生代的“绿化”是地球历史上最深刻的进化变化之一，因为维管植物占领了陆地表面。古生代早期至中期的海洋和大气事件与陆地植被的扩张有着广泛的联系，陆地植被的扩张减少了大气中的二氧化碳，促进了全球变冷，增加了向海洋的养分径流，并导致了海洋生物的灭绝。然而，令人惊讶的是，古生代河流几乎没有出现在这些讨论中，尽管早期的陆生植物占领了许多河流平原。先前有限的研究表明，当河流平原没有植被时，河道用沙子淹没了沿海地区，但在志留纪，由于植被稳定了河岸，出现了蜿蜒的河流和泥泞的洪泛平原。目前的研究计划旨在记录关键的寒武纪到泥盆纪时期（5.4亿到3.6亿年前）的河流沉积，将这些事件的时间与已知的早期植物的首次出现和丰富程度进行比较。在文献汇编之后，将在北美和欧洲选定的地点进行河流沉积物和一些世界上最早的植物组合的研究。在较年轻的石炭纪岩石中，我们正在研究山带内河流流域的植物，以便评估植物何时扩散到具有挑战性的内陆地区：然而，它们似乎从最早的时候就在那里了。我们还将探索野火的早期证据，微生物对河流平原的贡献，以及当植物足够大和丰富时促进通道转换的原木堵塞。

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.