Research from Stanford University has challenged the long-held belief that the evolution of land plants fundamentally altered river systems by shifting them from braided to meandering forms. The study, published in Science on August 21, suggests that unvegetated meandering rivers were more common throughout Earth’s history than previously thought.
Historically, geologists believed that before vegetation appeared on land about half a billion years ago, rivers primarily exhibited braided patterns—multiple channels weaving around sandy bars. Meandering rivers, with their single winding channels and associated floodplains, were thought to have developed only after plant life stabilized riverbanks.
The new research argues this interpretation is based on misreading geological evidence. According to the study’s lead author Michael Hasson, a PhD student at the Stanford Doerr School of Sustainability, “With our study, we’re pushing back on the widely accepted story of what landscapes looked like when plant life first evolved on land. We’re rewriting the story of the intertwined relationship between plants and rivers, which is a significant revision to our understanding of the history of the Earth.”
Meandering rivers are important for carbon storage because their floodplains can sequester large amounts of carbon over thousands of years. This process influences global climate by regulating atmospheric carbon dioxide levels over long timescales. Hasson explained: “Floodplains play an important role in determining how, when, and whether carbon is buried or released back into the atmosphere. Based on this work, we argue carbon storage in floodplains would have been common for much longer than the classic paradigm that assumes meandering rivers only occurred over the last several hundred million years.”
To assess how vegetation affects river channel patterns today, researchers analyzed satellite images showing about 4,500 bends across 49 modern meandering rivers with varying degrees of vegetation cover. They focused on point bars—sandy deposits forming inside river bends—and observed how these features migrate differently depending on vegetation presence.
For decades geologists used rock records—specifically sandstones and mudstones—to reconstruct ancient river styles by measuring bar migration angles. If little variation was found in bar migration direction within sandstone layers, it was assumed those rocks formed from braided rivers.
However, as senior author Mathieu Lapôtre noted: “In our paper, we show that this conclusion – which is taught in all geology curricula to this day – is most likely incorrect.” The team demonstrated that unvegetated meandering rivers can produce sedimentary signatures similar to those attributed to braided systems: “In other words,” Lapôtre said,”we show that if one were to use the same criterion geologists use in ancient rocks on modern rivers, meandering rivers would be miscategorized as braided rivers.”
These findings suggest scientists may need to revise models describing natural climate fluctuations throughout Earth’s history since carbon-rich floodplains could have existed far earlier and more extensively than previously recognized.
“Understanding how our planet is going to respond to human-induced climate change hinges on having an accurate baseline for how it has responded to past perturbations,” Hasson said.”The rock record provides that baseline but it’s only useful if we interpret it accurately.”
“We’re suggesting that an important control on carbon cycling – where carbon is stored,and for how long,due to river type and floodplain creation–hasn’t been fully understood,” he added.”Our study now points the way to better assessments.”
Researchers from University of Padova and University of British Columbia also contributed to this work.
