Low-gradient, single-threaded rivers prior to greening of the continents

Significance The origin of low-gradient meandering rivers—the primary conduits of water, carbon, and nutrients in present-day terrestrial landscapes—is considered coeval with Silurian-age plant evolution. It was hypothesized that pre-Silurian rivers lacked bank strength and were dominantly steep and braided, implying vastly different transport capacities of water and sediment. This idea, however, is inconsistent with the supercontinental-scale drainage of Neoproterozoic rivers, which requires unrealistically high mountains to achieve the necessary river gradients. Using geologic observations and paleohydraulic analyses, we show that pre-Silurian rivers were low-gradient, deep, and single-threaded—similar to modern meandering rivers. Results demonstrate uniformity of fluvial morphology despite a global revolution in Earth’s terrestrial biota, with ramifications for the topographic signature of life on Earth and other planets.